Advanced Bash-Scripting Guide:
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# Appendix A. Contributed Scripts

These scripts, while not fitting into the text of this document, do illustrate some interesting shell programming techniques. Some are useful, too. Have fun analyzing and running them.

Example A-1. mailformat: Formatting an e-mail message

    #!/bin/bash
    # mail-format.sh (ver. 1.1): Format e-mail messages.

    # Gets rid of carets, tabs, and also folds excessively long lines.

    # =================================================================
    #                 Standard Check for Script Argument(s)
    ARGS=1
    E_BADARGS=65
    E_NOFILE=66

    if [ $# -ne $ARGS ]  # Correct number of arguments passed to script?
    then
      echo "Usage: `basename $0` filename"
      exit $E_BADARGS
    fi

    if [ -f "$1" ]       # Check if file exists.
    then
        file_name=$1
    else
        echo "File \"$1\" does not exist."
        exit $E_NOFILE
    fi
    # =================================================================

    MAXWIDTH=70          # Width to fold excessively long lines to.

    # ---------------------------------
    # A variable can hold a sed script.
    sedscript='s/^>//
    s/^  *>//
    s/^  *//
    s/		*//'
    # ---------------------------------

    #  Delete carets and tabs at beginning of lines,
    #+ then fold lines to $MAXWIDTH characters.
    sed "$sedscript" $1 | fold -s --width=$MAXWIDTH
                            #  -s option to "fold"
                            #+ breaks lines at whitespace, if possible.

    #  This script was inspired by an article in a well-known trade journal
    #+ extolling a 164K MS Windows utility with similar functionality.
    #
    #  An nice set of text processing utilities and an efficient
    #+ scripting language provide an alternative to bloated executables.

    exit

Example A-2. rn: A simple-minded file renaming utility

This script is a modification of Example 16-22.

    #! /bin/bash
    # rn.sh

    # Very simpleminded filename "rename" utility (based on "lowercase.sh").
    #
    #  The "ren" utility, by Vladimir Lanin (lanin@csd2.nyu.edu),
    #+ does a much better job of this.

    ARGS=2
    E_BADARGS=85
    ONE=1                     # For getting singular/plural right (see below).

    if [ $# -ne "$ARGS" ]
    then
      echo "Usage: `basename $0` old-pattern new-pattern"
      # As in "rn gif jpg", which renames all gif files in working directory to jpg.
      exit $E_BADARGS
    fi

    number=0                  # Keeps track of how many files actually renamed.

    for filename in *$1*      #Traverse all matching files in directory.
    do
       if [ -f "$filename" ]  # If finds match...
       then
         fname=`basename $filename`            # Strip off path.
         n=`echo $fname | sed -e "s/$1/$2/"`   # Substitute new for old in filename.
         mv $fname $n                          # Rename.
         let "number += 1"
       fi
    done

    if [ "$number" -eq "$ONE" ]                # For correct grammar.
    then
     echo "$number file renamed."
    else
     echo "$number files renamed."
    fi

    exit $?

    # Exercises:
    # ---------
    # What types of files will this not work on?
    # How can this be fixed?

Example A-3. blank-rename: Renames filenames containing blanks

This is an even simpler-minded version of previous script.

    #! /bin/bash
    # blank-rename.sh
    #
    # Substitutes underscores for blanks in all the filenames in a directory.

    ONE=1                     # For getting singular/plural right (see below).
    number=0                  # Keeps track of how many files actually renamed.
    FOUND=0                   # Successful return value.

    for filename in *         #Traverse all files in directory.
    do
         echo "$filename" | grep -q " "         #  Check whether filename
         if [ $? -eq $FOUND ]                   #+ contains space(s).
         then
           fname=$filename                      # Yes, this filename needs work.
           n=`echo $fname | sed -e "s/ /_/g"`   # Substitute underscore for blank.
           mv "$fname" "$n"                     # Do the actual renaming.
           let "number += 1"
         fi
    done

    if [ "$number" -eq "$ONE" ]                 # For correct grammar.
    then
     echo "$number file renamed."
    else
     echo "$number files renamed."
    fi

    exit 0

Example A-4. encryptedpw: Uploading to an ftp site, using a locally encrypted password

    #!/bin/bash

    # Example "ex72.sh" modified to use encrypted password.

    #  Note that this is still rather insecure,
    #+ since the decrypted password is sent in the clear.
    #  Use something like "ssh" if this is a concern.

    E_BADARGS=85

    if [ -z "$1" ]
    then
      echo "Usage: `basename $0` filename"
      exit $E_BADARGS
    fi

    Username=bozo           # Change to suit.
    pword=/home/bozo/secret/password_encrypted.file
    # File containing encrypted password.

    Filename=`basename $1`  # Strips pathname out of file name.

    Server="XXX"
    Directory="YYY"         # Change above to actual server name & directory.

    Password=`cruft <$pword`          # Decrypt password.
    #  Uses the author's own "cruft" file encryption package,
    #+ based on the classic "onetime pad" algorithm,
    #+ and obtainable from:
    #+ Primary-site:   ftp://ibiblio.org/pub/Linux/utils/file
    #+                 cruft-0.2.tar.gz [16k]

    ftp -n $Server <<End-Of-Session
    user $Username $Password
    binary
    bell
    cd $Directory
    put $Filename
    bye
    End-Of-Session
    # -n option to "ftp" disables auto-logon.
    # Note that "bell" rings 'bell' after each file transfer.

    exit 0

Example A-5. copy-cd: Copying a data CD

    #!/bin/bash
    # copy-cd.sh: copying a data CD

    CDROM=/dev/cdrom                           # CD ROM device
    OF=/home/bozo/projects/cdimage.iso         # output file
    #       /xxxx/xxxxxxxx/                      Change to suit your system.
    BLOCKSIZE=2048
    # SPEED=10                                 # If unspecified, uses max spd.
    # DEVICE=/dev/cdrom                          older version.
    DEVICE="1,0,0"

    echo; echo "Insert source CD, but do *not* mount it."
    echo "Press ENTER when ready. "
    read ready                                 # Wait for input, $ready not used.

    echo; echo "Copying the source CD to $OF."
    echo "This may take a while. Please be patient."

    dd if=$CDROM of=$OF bs=$BLOCKSIZE          # Raw device copy.

    echo; echo "Remove data CD."
    echo "Insert blank CDR."
    echo "Press ENTER when ready. "
    read ready                                 # Wait for input, $ready not used.

    echo "Copying $OF to CDR."

    # cdrecord -v -isosize speed=$SPEED dev=$DEVICE $OF   # Old version.
    wodim -v -isosize dev=$DEVICE $OF
    # Uses Joerg Schilling's "cdrecord" package (see its docs).
    # http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord.html
    # Newer Linux distros may use "wodim" rather than "cdrecord" ...

    echo; echo "Done copying $OF to CDR on device $CDROM."

    echo "Do you want to erase the image file (y/n)? "  # Probably a huge file.
    read answer

    case "$answer" in
    [yY]) rm -f $OF
          echo "$OF erased."
          ;;
    *)    echo "$OF not erased.";;
    esac

    echo

    # Exercise:
    # Change the above "case" statement to also accept "yes" and "Yes" as input.

    exit 0

Example A-6. Collatz series

    #!/bin/bash
    # collatz.sh

    #  The notorious "hailstone" or Collatz series.
    #  -------------------------------------------
    #  1) Get the integer "seed" from the command-line.
    #  2) NUMBER <-- seed
    #  3) Print NUMBER.
    #  4)  If NUMBER is even, divide by 2, or
    #  5)+ if odd, multiply by 3 and add 1.
    #  6) NUMBER <-- result
    #  7) Loop back to step 3 (for specified number of iterations).
    #
    #  The theory is that every such sequence,
    #+ no matter how large the initial value,
    #+ eventually settles down to repeating "4,2,1..." cycles,
    #+ even after fluctuating through a wide range of values.
    #
    #  This is an instance of an "iterate,"
    #+ an operation that feeds its output back into its input.
    #  Sometimes the result is a "chaotic" series.

    MAX_ITERATIONS=200
    # For large seed numbers (>32000), try increasing MAX_ITERATIONS.

    h=${1:-$$}                      #  Seed.
                                    #  Use $PID as seed,
                                    #+ if not specified as command-line arg.

    echo
    echo "C($h) -*- $MAX_ITERATIONS Iterations"
    echo

    for ((i=1; i<=MAX_ITERATIONS; i++))
    do

    # echo -n "$h	"
    #            ^^^
    #            tab
    # printf does it better ...
    COLWIDTH=%7d
    printf $COLWIDTH $h

      let "remainder = h % 2"
      if [ "$remainder" -eq 0 ]   # Even?
      then
        let "h /= 2"              # Divide by 2.
      else
        let "h = h*3 + 1"         # Multiply by 3 and add 1.
      fi

    COLUMNS=10                    # Output 10 values per line.
    let "line_break = i % $COLUMNS"
    if [ "$line_break" -eq 0 ]
    then
      echo
    fi

    done

    echo

    #  For more information on this strange mathematical function,
    #+ see _Computers, Pattern, Chaos, and Beauty_, by Pickover, p. 185 ff.,
    #+ as listed in the bibliography.

    exit 0

Example A-7. days-between: Days between two dates

    #!/bin/bash
    # days-between.sh:    Number of days between two dates.
    # Usage: ./days-between.sh [M]M/[D]D/YYYY [M]M/[D]D/YYYY
    #
    # Note: Script modified to account for changes in Bash, v. 2.05b +,
    #+      that closed the loophole permitting large negative
    #+      integer return values.

    ARGS=2                # Two command-line parameters expected.
    E_PARAM_ERR=85        # Param error.

    REFYR=1600            # Reference year.
    CENTURY=100
    DIY=365
    ADJ_DIY=367           # Adjusted for leap year + fraction.
    MIY=12
    DIM=31
    LEAPCYCLE=4

    MAXRETVAL=255         #  Largest permissible
                          #+ positive return value from a function.

    diff=                 # Declare global variable for date difference.
    value=                # Declare global variable for absolute value.
    day=                  # Declare globals for day, month, year.
    month=
    year=

    Param_Error ()        # Command-line parameters wrong.
    {
      echo "Usage: `basename $0` [M]M/[D]D/YYYY [M]M/[D]D/YYYY"
      echo "       (date must be after 1/3/1600)"
      exit $E_PARAM_ERR
    }

    Parse_Date ()                 # Parse date from command-line params.
    {
      month=${1%%/**}
      dm=${1%/**}                 # Day and month.
      day=${dm#*/}
      let "year = `basename $1`"  # Not a filename, but works just the same.
    }

    check_date ()                 # Checks for invalid date(s) passed.
    {
      [ "$day" -gt "$DIM" ] || [ "$month" -gt "$MIY" ] ||
      [ "$year" -lt "$REFYR" ] && Param_Error
      # Exit script on bad value(s).
      # Uses or-list / and-list.
      #
      # Exercise: Implement more rigorous date checking.
    }

    strip_leading_zero () #  Better to strip possible leading zero(s)
    {                     #+ from day and/or month
      return ${1#0}       #+ since otherwise Bash will interpret them
    }                     #+ as octal values (POSIX.2, sect 2.9.2.1).

    day_index ()          # Gauss' Formula:
    {                     # Days from March 1, 1600 to date passed as param.
                          #           ^^^^^^^^^^^^^
      day=$1
      month=$2
      year=$3

      let "month = $month - 2"
      if [ "$month" -le 0 ]
      then
        let "month += 12"
        let "year -= 1"
      fi

      let "year -= $REFYR"
      let "indexyr = $year / $CENTURY"

      let "Days = $DIY*$year + $year/$LEAPCYCLE - $indexyr \
                  + $indexyr/$LEAPCYCLE + $ADJ_DIY*$month/$MIY + $day - $DIM"
      #  For an in-depth explanation of this algorithm, see
      #+   http://weblogs.asp.net/pgreborio/archive/2005/01/06/347968.aspx

      echo $Days

    }

    calculate_difference ()            # Difference between two day indices.
    {
      let "diff = $1 - $2"             # Global variable.
    }

    abs ()                             #  Absolute value
    {                                  #  Uses global "value" variable.
      if [ "$1" -lt 0 ]                #  If negative
      then                             #+ then
        let "value = 0 - $1"           #+ change sign,
      else                             #+ else
        let "value = $1"               #+ leave it alone.
      fi
    }

    if [ $# -ne "$ARGS" ]              # Require two command-line params.
    then
      Param_Error
    fi

    Parse_Date $1
    check_date $day $month $year       #  See if valid date.

    strip_leading_zero $day            #  Remove any leading zeroes
    day=$?                             #+ on day and/or month.
    strip_leading_zero $month
    month=$?

    let "date1 = `day_index $day $month $year`"

    Parse_Date $2
    check_date $day $month $year

    strip_leading_zero $day
    day=$?
    strip_leading_zero $month
    month=$?

    date2=$(day_index $day $month $year) # Command substitution.

    calculate_difference $date1 $date2

    abs $diff                            # Make sure it's positive.
    diff=$value

    echo $diff

    exit 0

    #  Exercise:
    #  --------
    #  If given only one command-line parameter, have the script
    #+ use today's date as the second.

    #  Compare this script with
    #+ the implementation of Gauss' Formula in a C program at
    #+    http://buschencrew.hypermart.net/software/datedif

Example A-8. Making a dictionary

    #!/bin/bash
    # makedict.sh  [make dictionary]

    # Modification of /usr/sbin/mkdict (/usr/sbin/cracklib-forman) script.
    # Original script copyright 1993, by Alec Muffett.
    #
    #  This modified script included in this document in a manner
    #+ consistent with the "LICENSE" document of the "Crack" package
    #+ that the original script is a part of.

    #  This script processes text files to produce a sorted list
    #+ of words found in the files.
    #  This may be useful for compiling dictionaries
    #+ and for other lexicographic purposes.

    E_BADARGS=65

    if [ ! -r "$1" ]                    #  Need at least one
    then                                #+ valid file argument.
      echo "Usage: $0 files-to-process"
      exit $E_BADARGS
    fi

    # SORT="sort"                       #  No longer necessary to define
                                        #+ options to sort. Changed from
                                        #+ original script.

    cat $* |                            # Contents of specified files to stdout.
            tr A-Z a-z |                # Convert to lowercase.
            tr ' ' '\012' |             # New: change spaces to newlines.
    #       tr -cd '\012[a-z][0-9]' |   #  Get rid of everything
                                        #+ non-alphanumeric (in orig. script).
            tr -c '\012a-z'  '\012' |   #  Rather than deleting non-alpha
                                        #+ chars, change them to newlines.
            sort |                      # $SORT options unnecessary now.
            uniq |                      # Remove duplicates.
            grep -v '^#' |              # Delete lines starting with hashmark.
            grep -v '^$'                # Delete blank lines.

    exit 0

Example A-9. Soundex conversion

    #!/bin/bash
    # soundex.sh: Calculate "soundex" code for names

    # =======================================================
    #        Soundex script
    #              by
    #         Mendel Cooper
    #     thegrendel.abs@gmail.com
    #     reldate: 23 January, 2002
    #
    #   Placed in the Public Domain.
    #
    # A slightly different version of this script appeared in
    #+ Ed Schaefer's July, 2002 "Shell Corner" column
    #+ in "Unix Review" on-line,
    #+ http://www.unixreview.com/documents/uni1026336632258/
    # =======================================================

    ARGCOUNT=1                     # Need name as argument.
    E_WRONGARGS=90

    if [ $# -ne "$ARGCOUNT" ]
    then
      echo "Usage: `basename $0` name"
      exit $E_WRONGARGS
    fi

    assign_value ()                #  Assigns numerical value
    {                              #+ to letters of name.

      val1=bfpv                    # 'b,f,p,v' = 1
      val2=cgjkqsxz                # 'c,g,j,k,q,s,x,z' = 2
      val3=dt                      #  etc.
      val4=l
      val5=mn
      val6=r

    # Exceptionally clever use of 'tr' follows.
    # Try to figure out what is going on here.

    value=$( echo "$1" \
    | tr -d wh \
    | tr $val1 1 | tr $val2 2 | tr $val3 3 \
    | tr $val4 4 | tr $val5 5 | tr $val6 6 \
    | tr -s 123456 \
    | tr -d aeiouy )

    # Assign letter values.
    # Remove duplicate numbers, except when separated by vowels.
    # Ignore vowels, except as separators, so delete them last.
    # Ignore 'w' and 'h', even as separators, so delete them first.
    #
    # The above command substitution lays more pipe than a plumber <g>.

    }

    input_name="$1"
    echo
    echo "Name = $input_name"

    # Change all characters of name input to lowercase.
    # ------------------------------------------------
    name=$( echo $input_name | tr A-Z a-z )
    # ------------------------------------------------
    # Just in case argument to script is mixed case.

    # Prefix of soundex code: first letter of name.
    # --------------------------------------------

    char_pos=0                     # Initialize character position.
    prefix0=${name:$char_pos:1}
    prefix=`echo $prefix0 | tr a-z A-Z`
                                   # Uppercase 1st letter of soundex.

    let "char_pos += 1"            # Bump character position to 2nd letter of name.
    name1=${name:$char_pos}

    # ++++++++++++++++++++++++++ Exception Patch ++++++++++++++++++++++++++++++
    #  Now, we run both the input name and the name shifted one char
    #+ to the right through the value-assigning function.
    #  If we get the same value out, that means that the first two characters
    #+ of the name have the same value assigned, and that one should cancel.
    #  However, we also need to test whether the first letter of the name
    #+ is a vowel or 'w' or 'h', because otherwise this would bollix things up.

    char1=`echo $prefix | tr A-Z a-z`    # First letter of name, lowercased.

    assign_value $name
    s1=$value
    assign_value $name1
    s2=$value
    assign_value $char1
    s3=$value
    s3=9$s3                              #  If first letter of name is a vowel
                                         #+ or 'w' or 'h',
                                         #+ then its "value" will be null (unset).
    				     #+ Therefore, set it to 9, an otherwise
    				     #+ unused value, which can be tested for.

    if [[ "$s1" -ne "$s2" || "$s3" -eq 9 ]]
    then
      suffix=$s2
    else
      suffix=${s2:$char_pos}
    fi
    # ++++++++++++++++++++++ end Exception Patch ++++++++++++++++++++++++++++++

    padding=000                    # Use at most 3 zeroes to pad.

    soun=$prefix$suffix$padding    # Pad with zeroes.

    MAXLEN=4                       # Truncate to maximum of 4 chars.
    soundex=${soun:0:$MAXLEN}

    echo "Soundex = $soundex"

    echo

    #  The soundex code is a method of indexing and classifying names
    #+ by grouping together the ones that sound alike.
    #  The soundex code for a given name is the first letter of the name,
    #+ followed by a calculated three-number code.
    #  Similar sounding names should have almost the same soundex codes.

    #   Examples:
    #   Smith and Smythe both have a "S-530" soundex.
    #   Harrison = H-625
    #   Hargison = H-622
    #   Harriman = H-655

    #  This works out fairly well in practice, but there are numerous anomalies.
    #
    #
    #  The U.S. Census and certain other governmental agencies use soundex,
    #  as do genealogical researchers.
    #
    #  For more information,
    #+ see the "National Archives and Records Administration home page",
    #+ http://www.nara.gov/genealogy/soundex/soundex.html

    # Exercise:
    # --------
    # Simplify the "Exception Patch" section of this script.

    exit 0

Example A-10. Game of Life

    #!/bin/bash
    # life.sh: "Life in the Slow Lane"
    # Author: Mendel Cooper
    # License: GPL3

    # Version 0.2:   Patched by Daniel Albers
    #+               to allow non-square grids as input.
    # Version 0.2.1: Added 2-second delay between generations.

    # ##################################################################### #
    # This is the Bash script version of John Conway's "Game of Life".      #
    # "Life" is a simple implementation of cellular automata.               #
    # --------------------------------------------------------------------- #
    # On a rectangular grid, let each "cell" be either "living" or "dead."  #
    # Designate a living cell with a dot, and a dead one with a blank space.#
    #      Begin with an arbitrarily drawn dot-and-blank grid,              #
    #+     and let this be the starting generation: generation 0.           #
    # Determine each successive generation by the following rules:          #
    #   1) Each cell has 8 neighbors, the adjoining cells                   #
    #+     left, right, top, bottom, and the 4 diagonals.                   #
    #                                                                       #
    #                       123                                             #
    #                       4*5     The * is the cell under consideration.  #
    #                       678                                             #
    #                                                                       #
    # 2) A living cell with either 2 or 3 living neighbors remains alive.   #
    SURVIVE=2                                                               #
    # 3) A dead cell with 3 living neighbors comes alive, a "birth."        #
    BIRTH=3                                                                 #
    # 4) All other cases result in a dead cell for the next generation.     #
    # ##################################################################### #

    startfile=gen0   # Read the starting generation from the file "gen0" ...
                     # Default, if no other file specified when invoking script.
                     #
    if [ -n "$1" ]   # Specify another "generation 0" file.
    then
        startfile="$1"
    fi

    ############################################
    #  Abort script if "startfile" not specified
    #+ and
    #+ default file "gen0" not present.

    E_NOSTARTFILE=86

    if [ ! -e "$startfile" ]
    then
      echo "Startfile \""$startfile"\" missing!"
      exit $E_NOSTARTFILE
    fi
    ############################################

    ALIVE1=.
    DEAD1=_
                     # Represent living and dead cells in the start-up file.

    #  -----------------------------------------------------#
    #  This script uses a 10 x 10 grid (may be increased,
    #+ but a large grid will slow down execution).
    ROWS=10
    COLS=10
    #  Change above two variables to match desired grid size.
    #  -----------------------------------------------------#

    GENERATIONS=10          #  How many generations to cycle through.
                            #  Adjust this upwards
                            #+ if you have time on your hands.

    NONE_ALIVE=85           #  Exit status on premature bailout,
                            #+ if no cells left alive.
    DELAY=2                 #  Pause between generations.
    TRUE=0
    FALSE=1
    ALIVE=0
    DEAD=1

    avar=                   # Global; holds current generation.
    generation=0            # Initialize generation count.

    # =================================================================

    let "cells = $ROWS * $COLS"   # How many cells.

    # Arrays containing "cells."
    declare -a initial
    declare -a current

    display ()
    {

    alive=0                 # How many cells alive at any given time.
                            # Initially zero.

    declare -a arr
    arr=( `echo "$1"` )     # Convert passed arg to array.

    element_count=${#arr[*]}

    local i
    local rowcheck

    for ((i=0; i<$element_count; i++))
    do

      # Insert newline at end of each row.
      let "rowcheck = $i % COLS"
      if [ "$rowcheck" -eq 0 ]
      then
        echo                # Newline.
        echo -n "      "    # Indent.
      fi

      cell=${arr[i]}

      if [ "$cell" = . ]
      then
        let "alive += 1"
      fi

      echo -n "$cell" | sed -e 's/_/ /g'
      # Print out array, changing underscores to spaces.
    done

    return

    }

    IsValid ()                            # Test if cell coordinate valid.
    {

      if [ -z "$1"  -o -z "$2" ]          # Mandatory arguments missing?
      then
        return $FALSE
      fi

    local row
    local lower_limit=0                   # Disallow negative coordinate.
    local upper_limit
    local left
    local right

    let "upper_limit = $ROWS * $COLS - 1" # Total number of cells.

    if [ "$1" -lt "$lower_limit" -o "$1" -gt "$upper_limit" ]
    then
      return $FALSE                       # Out of array bounds.
    fi

    row=$2
    let "left = $row * $COLS"             # Left limit.
    let "right = $left + $COLS - 1"       # Right limit.

    if [ "$1" -lt "$left" -o "$1" -gt "$right" ]
    then
      return $FALSE                       # Beyond row boundary.
    fi

    return $TRUE                          # Valid coordinate.

    }

    IsAlive ()              #  Test whether cell is alive.
                            #  Takes array, cell number, and
    {                       #+ state of cell as arguments.
      GetCount "$1" $2      #  Get alive cell count in neighborhood.
      local nhbd=$?

      if [ "$nhbd" -eq "$BIRTH" ]  # Alive in any case.
      then
        return $ALIVE
      fi

      if [ "$3" = "." -a "$nhbd" -eq "$SURVIVE" ]
      then                  # Alive only if previously alive.
        return $ALIVE
      fi

      return $DEAD          # Defaults to dead.

    }

    GetCount ()             # Count live cells in passed cell's neighborhood.
                            # Two arguments needed:
    			# $1) variable holding array
    			# $2) cell number
    {
      local cell_number=$2
      local array
      local top
      local center
      local bottom
      local r
      local row
      local i
      local t_top
      local t_cen
      local t_bot
      local count=0
      local ROW_NHBD=3

      array=( `echo "$1"` )

      let "top = $cell_number - $COLS - 1"    # Set up cell neighborhood.
      let "center = $cell_number - 1"
      let "bottom = $cell_number + $COLS - 1"
      let "r = $cell_number / $COLS"

      for ((i=0; i<$ROW_NHBD; i++))           # Traverse from left to right.
      do
        let "t_top = $top + $i"
        let "t_cen = $center + $i"
        let "t_bot = $bottom + $i"

        let "row = $r"                        # Count center row.
        IsValid $t_cen $row                   # Valid cell position?
        if [ $? -eq "$TRUE" ]
        then
          if [ ${array[$t_cen]} = "$ALIVE1" ] # Is it alive?
          then                                # If yes, then ...
            let "count += 1"                  # Increment count.
          fi
        fi

        let "row = $r - 1"                    # Count top row.
        IsValid $t_top $row
        if [ $? -eq "$TRUE" ]
        then
          if [ ${array[$t_top]} = "$ALIVE1" ] # Redundancy here.
          then                                # Can it be optimized?
            let "count += 1"
          fi
        fi

        let "row = $r + 1"                    # Count bottom row.
        IsValid $t_bot $row
        if [ $? -eq "$TRUE" ]
        then
          if [ ${array[$t_bot]} = "$ALIVE1" ]
          then
            let "count += 1"
          fi
        fi

      done

      if [ ${array[$cell_number]} = "$ALIVE1" ]
      then
        let "count -= 1"        #  Make sure value of tested cell itself
      fi                        #+ is not counted.

      return $count

    }

    next_gen ()               # Update generation array.
    {

    local array
    local i=0

    array=( `echo "$1"` )     # Convert passed arg to array.

    while [ "$i" -lt "$cells" ]
    do
      IsAlive "$1" $i ${array[$i]}   # Is the cell alive?
      if [ $? -eq "$ALIVE" ]
      then                           #  If alive, then
        array[$i]=.                  #+ represent the cell as a period.
      else
        array[$i]="_"                #  Otherwise underscore
       fi                            #+ (will later be converted to space).
      let "i += 1"
    done

    #    let "generation += 1"       # Increment generation count.
    ###  Why was the above line commented out?

    # Set variable to pass as parameter to "display" function.
    avar=`echo ${array[@]}`   # Convert array back to string variable.
    display "$avar"           # Display it.
    echo; echo
    echo "Generation $generation  -  $alive alive"

    if [ "$alive" -eq 0 ]
    then
      echo
      echo "Premature exit: no more cells alive!"
      exit $NONE_ALIVE        #  No point in continuing
    fi                        #+ if no live cells.

    }

    # =========================================================

    # main ()
    # {

    # Load initial array with contents of startup file.
    initial=( `cat "$startfile" | sed -e '/#/d' | tr -d '\n' |\
    # Delete lines containing '#' comment character.
               sed -e 's/\./\. /g' -e 's/_/_ /g'` )
    # Remove linefeeds and insert space between elements.

    clear          # Clear screen.

    echo #         Title
    setterm -reverse on
    echo "======================="
    setterm -reverse off
    echo "    $GENERATIONS generations"
    echo "           of"
    echo "\"Life in the Slow Lane\""
    setterm -reverse on
    echo "======================="
    setterm -reverse off

    sleep $DELAY   # Display "splash screen" for 2 seconds.

    # -------- Display first generation. --------
    Gen0=`echo ${initial[@]}`
    display "$Gen0"           # Display only.
    echo; echo
    echo "Generation $generation  -  $alive alive"
    sleep $DELAY
    # -------------------------------------------

    let "generation += 1"     # Bump generation count.
    echo

    # ------- Display second generation. -------
    Cur=`echo ${initial[@]}`
    next_gen "$Cur"          # Update & display.
    sleep $DELAY
    # ------------------------------------------

    let "generation += 1"     # Increment generation count.

    # ------ Main loop for displaying subsequent generations ------
    while [ "$generation" -le "$GENERATIONS" ]
    do
      Cur="$avar"
      next_gen "$Cur"
      let "generation += 1"
      sleep $DELAY
    done
    # ==============================================================

    echo
    # }

    exit 0   # CEOF:EOF

    # The grid in this script has a "boundary problem."
    # The the top, bottom, and sides border on a void of dead cells.
    # Exercise: Change the script to have the grid wrap around,
    # +         so that the left and right sides will "touch,"
    # +         as will the top and bottom.
    #
    # Exercise: Create a new "gen0" file to seed this script.
    #           Use a 12 x 16 grid, instead of the original 10 x 10 one.
    #           Make the necessary changes to the script,
    #+          so it will run with the altered file.
    #
    # Exercise: Modify this script so that it can determine the grid size
    #+          from the "gen0" file, and set any variables necessary
    #+          for the script to run.
    #           This would make unnecessary any changes to variables
    #+          in the script for an altered grid size.
    #
    # Exercise: Optimize this script.
    #           It has redundant code.

Example A-11. Data file for Game of Life

    # gen0
    #
    # This is an example "generation 0" start-up file for "life.sh".
    # --------------------------------------------------------------
    #  The "gen0" file is a 10 x 10 grid using a period (.) for live cells,
    #+ and an underscore (_) for dead ones. We cannot simply use spaces
    #+ for dead cells in this file because of a peculiarity in Bash arrays.
    #  [Exercise for the reader: explain this.]
    #
    # Lines beginning with a '#' are comments, and the script ignores them.
    __.__..___
    __.._.____
    ____.___..
    _._______.
    ____._____
    ..__...___
    ____._____
    ___...____
    __.._..___
    _..___..__

+++

The following script is by Mark Moraes of the University of Toronto. See the file `Moraes-COPYRIGHT` for permissions and restrictions. This file is included in the combined HTML/source tarball of the ABS Guide.

Example A-12. behead: Removing mail and news message headers

    #! /bin/sh
    #  Strips off the header from a mail/News message i.e. till the first
    #+ empty line.
    #  Author: Mark Moraes, University of Toronto

    # ==> These comments added by author of this document.

    if [ $# -eq 0 ]; then
    # ==> If no command-line args present, then works on file redirected to stdin.
    	sed -e '1,/^$/d' -e '/^[ 	]*$/d'
    	# --> Delete empty lines and all lines until
    	# --> first one beginning with white space.
    else
    # ==> If command-line args present, then work on files named.
    	for i do
    		sed -e '1,/^$/d' -e '/^[ 	]*$/d' $i
    		# --> Ditto, as above.
    	done
    fi

    exit

    # ==> Exercise: Add error checking and other options.
    # ==>
    # ==> Note that the small sed script repeats, except for the arg passed.
    # ==> Does it make sense to embed it in a function? Why or why not?

    /*
     * Copyright University of Toronto 1988, 1989.
     * Written by Mark Moraes
     *
     * Permission is granted to anyone to use this software for any purpose on
     * any computer system, and to alter it and redistribute it freely, subject
     * to the following restrictions:
     *
     * 1. The author and the University of Toronto are not responsible
     *    for the consequences of use of this software, no matter how awful,
     *    even if they arise from flaws in it.
     *
     * 2. The origin of this software must not be misrepresented, either by
     *    explicit claim or by omission.  Since few users ever read sources,
     *    credits must appear in the documentation.
     *
     * 3. Altered versions must be plainly marked as such, and must not be
     *    misrepresented as being the original software.  Since few users
     *    ever read sources, credits must appear in the documentation.
     *
     * 4. This notice may not be removed or altered.
     */

+

Antek Sawicki contributed the following script, which makes very clever use of the parameter substitution operators discussed in Section 10.2.

Example A-13. password: Generating random 8-character passwords

    #!/bin/bash
    #
    #
    #  Random password generator for Bash 2.x +
    #+ by Antek Sawicki <tenox@tenox.tc>,
    #+ who generously gave usage permission to the ABS Guide author.
    #
    # ==> Comments added by document author ==>

    MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
    # ==> Password will consist of alphanumeric characters.
    LENGTH="8"
    # ==> May change 'LENGTH' for longer password.

    while [ "${n:=1}" -le "$LENGTH" ]
    # ==> Recall that := is "default substitution" operator.
    # ==> So, if 'n' has not been initialized, set it to 1.
    do
    	PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
    	# ==> Very clever, but tricky.

    	# ==> Starting from the innermost nesting...
    	# ==> ${#MATRIX} returns length of array MATRIX.

    	# ==> $RANDOM%${#MATRIX} returns random number between 1
    	# ==> and [length of MATRIX] - 1.

    	# ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
    	# ==> returns expansion of MATRIX at random position, by length 1.
    	# ==> See {var:pos:len} parameter substitution in Chapter 9.
    	# ==> and the associated examples.

    	# ==> PASS=... simply pastes this result onto previous PASS (concatenation).

    	# ==> To visualize this more clearly, uncomment the following line
    	#                 echo "$PASS"
    	# ==> to see PASS being built up,
    	# ==> one character at a time, each iteration of the loop.

    	let n+=1
    	# ==> Increment 'n' for next pass.
    done

    echo "$PASS"      # ==> Or, redirect to a file, as desired.

    exit 0

+

James R. Van Zandt contributed this script which uses named pipes and, in his words, "really exercises quoting and escaping."

Example A-14. fifo: Making daily backups, using named pipes

    #!/bin/bash
    # ==> Script by James R. Van Zandt, and used here with his permission.

    # ==> Comments added by author of this document.

      HERE=`uname -n`    # ==> hostname
      THERE=bilbo
      echo "starting remote backup to $THERE at `date +%r`"
      # ==> `date +%r` returns time in 12-hour format, i.e. "08:08:34 PM".

      # make sure /pipe really is a pipe and not a plain file
      rm -rf /pipe
      mkfifo /pipe       # ==> Create a "named pipe", named "/pipe" ...

      # ==> 'su xyz' runs commands as user "xyz".
      # ==> 'ssh' invokes secure shell (remote login client).
      su xyz -c "ssh $THERE \"cat > /home/xyz/backup/${HERE}-daily.tar.gz\" < /pipe"&
      cd /
      tar -czf - bin boot dev etc home info lib man root sbin share usr var > /pipe
      # ==> Uses named pipe, /pipe, to communicate between processes:
      # ==> 'tar/gzip' writes to /pipe and 'ssh' reads from /pipe.

      # ==> The end result is this backs up the main directories, from / on down.

      # ==>  What are the advantages of a "named pipe" in this situation,
      # ==>+ as opposed to an "anonymous pipe", with |?
      # ==>  Will an anonymous pipe even work here?

      # ==>  Is it necessary to delete the pipe before exiting the script?
      # ==>  How could that be done?

      exit 0

+

Stéphane Chazelas used the following script to demonstrate generating prime numbers without arrays.

Example A-15. Generating prime numbers using the modulo operator

    #!/bin/bash
    # primes.sh: Generate prime numbers, without using arrays.
    # Script contributed by Stephane Chazelas.

    #  This does *not* use the classic "Sieve of Eratosthenes" algorithm,
    #+ but instead the more intuitive method of testing each candidate number
    #+ for factors (divisors), using the "%" modulo operator.

    LIMIT=1000                    # Primes, 2 ... 1000.

    Primes()
    {
     (( n = $1 + 1 ))             # Bump to next integer.
     shift                        # Next parameter in list.
    #  echo "_n=$n i=$i_"

     if (( n == LIMIT ))
     then echo $*
     return
     fi

     for i; do                    # "i" set to "@", previous values of $n.
    #   echo "-n=$n i=$i-"
       (( i * i > n )) && break   # Optimization.
       (( n % i )) && continue    # Sift out non-primes using modulo operator.
       Primes $n $@               # Recursion inside loop.
       return
       done

       Primes $n $@ $n            #  Recursion outside loop.
                                  #  Successively accumulate
    			      #+ positional parameters.
                                  #  "$@" is the accumulating list of primes.
    }

    Primes 1

    exit $?

    # Pipe output of the script to 'fmt' for prettier printing.

    #  Uncomment lines 16 and 24 to help figure out what is going on.

    #  Compare the speed of this algorithm for generating primes
    #+ with the Sieve of Eratosthenes (ex68.sh).

    #  Exercise: Rewrite this script without recursion.

+

Rick Boivie's revision of Jordi Sanfeliu's tree script.

Example A-16. tree: Displaying a directory tree

    #!/bin/bash
    # tree.sh

    #  Written by Rick Boivie.
    #  Used with permission.
    #  This is a revised and simplified version of a script
    #+ by Jordi Sanfeliu (the original author), and patched by Ian Kjos.
    #  This script replaces the earlier version used in
    #+ previous releases of the Advanced Bash Scripting Guide.
    #  Copyright (c) 2002, by Jordi Sanfeliu, Rick Boivie, and Ian Kjos.

    # ==> Comments added by the author of this document.

    search () {
    for dir in `echo *`
    #  ==> `echo *` lists all the files in current working directory,
    #+ ==> without line breaks.
    #  ==> Similar effect to for dir in *
    #  ==> but "dir in `echo *`" will not handle filenames with blanks.
    do
      if [ -d "$dir" ] ; then # ==> If it is a directory (-d)...
      zz=0                    # ==> Temp variable, keeping track of
                              #     directory level.
      while [ $zz != $1 ]     # Keep track of inner nested loop.
        do
          echo -n "| "        # ==> Display vertical connector symbol,
                              # ==> with 2 spaces & no line feed
                              #     in order to indent.
          zz=`expr $zz + 1`   # ==> Increment zz.
        done

        if [ -L "$dir" ] ; then # ==> If directory is a symbolic link...
          echo "+---$dir" `ls -l $dir | sed 's/^.*'$dir' //'`
          # ==> Display horiz. connector and list directory name, but...
          # ==> delete date/time part of long listing.
        else
          echo "+---$dir"       # ==> Display horizontal connector symbol...
          # ==> and print directory name.
          numdirs=`expr $numdirs + 1` # ==> Increment directory count.
          if cd "$dir" ; then         # ==> If can move to subdirectory...
            search `expr $1 + 1`      # with recursion ;-)
            # ==> Function calls itself.
            cd ..
          fi
        fi
      fi
    done
    }

    if [ $# != 0 ] ; then
      cd $1   # Move to indicated directory.
      #else   # stay in current directory
    fi

    echo "Initial directory = `pwd`"
    numdirs=0

    search 0
    echo "Total directories = $numdirs"

    exit 0

Patsie's version of a directory tree script.

Example A-17. tree2: Alternate directory tree script

    #!/bin/bash
    # tree2.sh

    # Lightly modified/reformatted by ABS Guide author.
    # Included in ABS Guide with permission of script author (thanks!).

    ## Recursive file/dirsize checking script, by Patsie
    ##
    ## This script builds a list of files/directories and their size (du -akx)
    ## and processes this list to a human readable tree shape
    ## The 'du -akx' is only as good as the permissions the owner has.
    ## So preferably run as root* to get the best results, or use only on
    ## directories for which you have read permissions. Anything you can't
    ## read is not in the list.

    #* ABS Guide author advises caution when running scripts as root!

    ##########  THIS IS CONFIGURABLE  ##########

    TOP=5                   # Top 5 biggest (sub)directories.
    MAXRECURS=5             # Max 5 subdirectories/recursions deep.
    E_BL=80                 # Blank line already returned.
    E_DIR=81                # Directory not specified.

    ##########  DON'T CHANGE ANYTHING BELOW THIS LINE  ##########

    PID=$$                            # Our own process ID.
    SELF=`basename $0`                # Our own program name.
    TMP="/tmp/${SELF}.${PID}.tmp"     # Temporary 'du' result.

    # Convert number to dotted thousand.
    function dot { echo "            $*" |
                   sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta' |
                   tail -c 12; }

    # Usage: tree <recursion> <indent prefix> <min size> <directory>
    function tree {
      recurs="$1"           # How deep nested are we?
      prefix="$2"           # What do we display before file/dirname?
      minsize="$3"          # What is the minumum file/dirsize?
      dirname="$4"          # Which directory are we checking?

    # Get ($TOP) biggest subdirs/subfiles from TMP file.
      LIST=`egrep "[[:space:]]${dirname}/[^/]*$" "$TMP" |
            awk '{if($1>'$minsize') print;}' | sort -nr | head -$TOP`
      [ -z "$LIST" ] && return        # Empty list, then go back.

      cnt=0
      num=`echo "$LIST" | wc -l`      # How many entries in the list.

      ## Main loop
      echo "$LIST" | while read size name; do
        ((cnt+=1))		          # Count entry number.
        bname=`basename "$name"`      # We only need a basename of the entry.
        [ -d "$name" ] && bname="$bname/"
                                      # If it's a directory, append a slash.
        echo "`dot $size`$prefix +-$bname"
                                      # Display the result.
        #  Call ourself recursively if it's a directory
        #+ and we're not nested too deep ($MAXRECURS).
        #  The recursion goes up: $((recurs+1))
        #  The prefix gets a space if it's the last entry,
        #+ or a pipe if there are more entries.
        #  The minimum file/dirsize becomes
        #+ a tenth of his parent: $((size/10)).
        # Last argument is the full directory name to check.
        if [ -d "$name" -a $recurs -lt $MAXRECURS ]; then
          [ $cnt -lt $num ] \
            || (tree $((recurs+1)) "$prefix  " $((size/10)) "$name") \
            && (tree $((recurs+1)) "$prefix |" $((size/10)) "$name")
        fi
      done

      [ $? -eq 0 ] && echo "           $prefix"
      # Every time we jump back add a 'blank' line.
      return $E_BL
      # We return 80 to tell we added a blank line already.
    }

    ###                ###
    ###  main program  ###
    ###                ###

    rootdir="$@"
    [ -d "$rootdir" ] ||
      { echo "$SELF: Usage: $SELF <directory>" >&2; exit $E_DIR; }
      # We should be called with a directory name.

    echo "Building inventory list, please wait ..."
         # Show "please wait" message.
    du -akx "$rootdir" 1>"$TMP" 2>/dev/null
         # Build a temporary list of all files/dirs and their size.
    size=`tail -1 "$TMP" | awk '{print $1}'`
         # What is our rootdirectory's size?
    echo "`dot $size` $rootdir"
         # Display rootdirectory's entry.
    tree 0 "" 0 "$rootdir"
         # Display the tree below our rootdirectory.

    rm "$TMP" 2>/dev/null
         # Clean up TMP file.

    exit $?

Noah Friedman permitted use of his string function script. It essentially reproduces some of the C-library string manipulation functions.

Example A-18. string functions: C-style string functions

    #!/bin/bash

    # string.bash --- bash emulation of string(3) library routines
    # Author: Noah Friedman <friedman@prep.ai.mit.edu>
    # ==>     Used with his kind permission in this document.
    # Created: 1992-07-01
    # Last modified: 1993-09-29
    # Public domain

    # Conversion to bash v2 syntax done by Chet Ramey

    # Commentary:
    # Code:

    #:docstring strcat:
    # Usage: strcat s1 s2
    #
    # Strcat appends the value of variable s2 to variable s1.
    #
    # Example:
    #    a="foo"
    #    b="bar"
    #    strcat a b
    #    echo $a
    #    => foobar
    #
    #:end docstring:

    ###;;;autoload   ==> Autoloading of function commented out.
    function strcat ()
    {
        local s1_val s2_val

        s1_val=${!1}                        # indirect variable expansion
        s2_val=${!2}
        eval "$1"=\'"${s1_val}${s2_val}"\'
        # ==> eval $1='${s1_val}${s2_val}' avoids problems,
        # ==> if one of the variables contains a single quote.
    }

    #:docstring strncat:
    # Usage: strncat s1 s2 $n
    #
    # Line strcat, but strncat appends a maximum of n characters from the value
    # of variable s2.  It copies fewer if the value of variabl s2 is shorter
    # than n characters.  Echoes result on stdout.
    #
    # Example:
    #    a=foo
    #    b=barbaz
    #    strncat a b 3
    #    echo $a
    #    => foobar
    #
    #:end docstring:

    ###;;;autoload
    function strncat ()
    {
        local s1="$1"
        local s2="$2"
        local -i n="$3"
        local s1_val s2_val

        s1_val=${!s1}                       # ==> indirect variable expansion
        s2_val=${!s2}

        if [ ${#s2_val} -gt ${n} ]; then
           s2_val=${s2_val:0:$n}            # ==> substring extraction
        fi

        eval "$s1"=\'"${s1_val}${s2_val}"\'
        # ==> eval $1='${s1_val}${s2_val}' avoids problems,
        # ==> if one of the variables contains a single quote.
    }

    #:docstring strcmp:
    # Usage: strcmp $s1 $s2
    #
    # Strcmp compares its arguments and returns an integer less than, equal to,
    # or greater than zero, depending on whether string s1 is lexicographically
    # less than, equal to, or greater than string s2.
    #:end docstring:

    ###;;;autoload
    function strcmp ()
    {
        [ "$1" = "$2" ] && return 0

        [ "${1}" '<' "${2}" ] > /dev/null && return -1

        return 1
    }

    #:docstring strncmp:
    # Usage: strncmp $s1 $s2 $n
    #
    # Like strcmp, but makes the comparison by examining a maximum of n
    # characters (n less than or equal to zero yields equality).
    #:end docstring:

    ###;;;autoload
    function strncmp ()
    {
        if [ -z "${3}" -o "${3}" -le "0" ]; then
           return 0
        fi

        if [ ${3} -ge ${#1} -a ${3} -ge ${#2} ]; then
           strcmp "$1" "$2"
           return $?
        else
           s1=${1:0:$3}
           s2=${2:0:$3}
           strcmp $s1 $s2
           return $?
        fi
    }

    #:docstring strlen:
    # Usage: strlen s
    #
    # Strlen returns the number of characters in string literal s.
    #:end docstring:

    ###;;;autoload
    function strlen ()
    {
        eval echo "\${#${1}}"
        # ==> Returns the length of the value of the variable
        # ==> whose name is passed as an argument.
    }

    #:docstring strspn:
    # Usage: strspn $s1 $s2
    #
    # Strspn returns the length of the maximum initial segment of string s1,
    # which consists entirely of characters from string s2.
    #:end docstring:

    ###;;;autoload
    function strspn ()
    {
        # Unsetting IFS allows whitespace to be handled as normal chars.
        local IFS=
        local result="${1%%[!${2}]*}"

        echo ${#result}
    }

    #:docstring strcspn:
    # Usage: strcspn $s1 $s2
    #
    # Strcspn returns the length of the maximum initial segment of string s1,
    # which consists entirely of characters not from string s2.
    #:end docstring:

    ###;;;autoload
    function strcspn ()
    {
        # Unsetting IFS allows whitspace to be handled as normal chars.
        local IFS=
        local result="${1%%[${2}]*}"

        echo ${#result}
    }

    #:docstring strstr:
    # Usage: strstr s1 s2
    #
    # Strstr echoes a substring starting at the first occurrence of string s2 in
    # string s1, or nothing if s2 does not occur in the string.  If s2 points to
    # a string of zero length, strstr echoes s1.
    #:end docstring:

    ###;;;autoload
    function strstr ()
    {
        # if s2 points to a string of zero length, strstr echoes s1
        [ ${#2} -eq 0 ] && { echo "$1" ; return 0; }

        # strstr echoes nothing if s2 does not occur in s1
        case "$1" in
        *$2*) ;;
        *) return 1;;
        esac

        # use the pattern matching code to strip off the match and everything
        # following it
        first=${1/$2*/}

        # then strip off the first unmatched portion of the string
        echo "${1##$first}"
    }

    #:docstring strtok:
    # Usage: strtok s1 s2
    #
    # Strtok considers the string s1 to consist of a sequence of zero or more
    # text tokens separated by spans of one or more characters from the
    # separator string s2.  The first call (with a non-empty string s1
    # specified) echoes a string consisting of the first token on stdout. The
    # function keeps track of its position in the string s1 between separate
    # calls, so that subsequent calls made with the first argument an empty
    # string will work through the string immediately following that token.  In
    # this way subsequent calls will work through the string s1 until no tokens
    # remain.  The separator string s2 may be different from call to call.
    # When no token remains in s1, an empty value is echoed on stdout.
    #:end docstring:

    ###;;;autoload
    function strtok ()
    {
     :
    }

    #:docstring strtrunc:
    # Usage: strtrunc $n $s1 {$s2} {$...}
    #
    # Used by many functions like strncmp to truncate arguments for comparison.
    # Echoes the first n characters of each string s1 s2 ... on stdout.
    #:end docstring:

    ###;;;autoload
    function strtrunc ()
    {
        n=$1 ; shift
        for z; do
            echo "${z:0:$n}"
        done
    }

    # provide string

    # string.bash ends here

    # ========================================================================== #
    # ==> Everything below here added by the document author.

    # ==> Suggested use of this script is to delete everything below here,
    # ==> and "source" this file into your own scripts.

    # strcat
    string0=one
    string1=two
    echo
    echo "Testing \"strcat\" function:"
    echo "Original \"string0\" = $string0"
    echo "\"string1\" = $string1"
    strcat string0 string1
    echo "New \"string0\" = $string0"
    echo

    # strlen
    echo
    echo "Testing \"strlen\" function:"
    str=123456789
    echo "\"str\" = $str"
    echo -n "Length of \"str\" = "
    strlen str
    echo

    # Exercise:
    # --------
    # Add code to test all the other string functions above.

    exit 0

Michael Zick's complex array example uses the md5sum check sum command to encode directory information.

Example A-19. Directory information

    #! /bin/bash
    # directory-info.sh
    # Parses and lists directory information.

    # NOTE: Change lines 273 and 353 per "README" file.

    # Michael Zick is the author of this script.
    # Used here with his permission.

    # Controls
    # If overridden by command arguments, they must be in the order:
    #   Arg1: "Descriptor Directory"
    #   Arg2: "Exclude Paths"
    #   Arg3: "Exclude Directories"
    #
    # Environment Settings override Defaults.
    # Command arguments override Environment Settings.

    # Default location for content addressed file descriptors.
    MD5UCFS=${1:-${MD5UCFS:-'/tmpfs/ucfs'}}

    # Directory paths never to list or enter
    declare -a \
      EXCLUDE_PATHS=${2:-${EXCLUDE_PATHS:-'(/proc /dev /devfs /tmpfs)'}}

    # Directories never to list or enter
    declare -a \
      EXCLUDE_DIRS=${3:-${EXCLUDE_DIRS:-'(ucfs lost+found tmp wtmp)'}}

    # Files never to list or enter
    declare -a \
      EXCLUDE_FILES=${3:-${EXCLUDE_FILES:-'(core "Name with Spaces")'}}

    # Here document used as a comment block.
    : <<LSfieldsDoc
    # # # # # List Filesystem Directory Information # # # # #
    #
    #	ListDirectory "FileGlob" "Field-Array-Name"
    # or
    #	ListDirectory -of "FileGlob" "Field-Array-Filename"
    #	'-of' meaning 'output to filename'
    # # # # #

    String format description based on: ls (GNU fileutils) version 4.0.36

    Produces a line (or more) formatted:
    inode permissions hard-links owner group ...
    32736 -rw-------    1 mszick   mszick

    size    day month date hh:mm:ss year path
    2756608 Sun Apr 20 08:53:06 2003 /home/mszick/core

    Unless it is formatted:
    inode permissions hard-links owner group ...
    266705 crw-rw----    1    root  uucp

    major minor day month date hh:mm:ss year path
    4,  68 Sun Apr 20 09:27:33 2003 /dev/ttyS4
    NOTE: that pesky comma after the major number

    NOTE: the 'path' may be multiple fields:
    /home/mszick/core
    /proc/982/fd/0 -> /dev/null
    /proc/982/fd/1 -> /home/mszick/.xsession-errors
    /proc/982/fd/13 -> /tmp/tmpfZVVOCs (deleted)
    /proc/982/fd/7 -> /tmp/kde-mszick/ksycoca
    /proc/982/fd/8 -> socket:[11586]
    /proc/982/fd/9 -> pipe:[11588]

    If that isn't enough to keep your parser guessing,
    either or both of the path components may be relative:
    ../Built-Shared -> Built-Static
    ../linux-2.4.20.tar.bz2 -> ../../../SRCS/linux-2.4.20.tar.bz2

    The first character of the 11 (10?) character permissions field:
    's' Socket
    'd' Directory
    'b' Block device
    'c' Character device
    'l' Symbolic link
    NOTE: Hard links not marked - test for identical inode numbers
    on identical filesystems.
    All information about hard linked files are shared, except
    for the names and the name's location in the directory system.
    NOTE: A "Hard link" is known as a "File Alias" on some systems.
    '-' An undistingushed file

    Followed by three groups of letters for: User, Group, Others
    Character 1: '-' Not readable; 'r' Readable
    Character 2: '-' Not writable; 'w' Writable
    Character 3, User and Group: Combined execute and special
    '-' Not Executable, Not Special
    'x' Executable, Not Special
    's' Executable, Special
    'S' Not Executable, Special
    Character 3, Others: Combined execute and sticky (tacky?)
    '-' Not Executable, Not Tacky
    'x' Executable, Not Tacky
    't' Executable, Tacky
    'T' Not Executable, Tacky

    Followed by an access indicator
    Haven't tested this one, it may be the eleventh character
    or it may generate another field
    ' ' No alternate access
    '+' Alternate access
    LSfieldsDoc

    ListDirectory()
    {
    	local -a T
    	local -i of=0		# Default return in variable
    #	OLD_IFS=$IFS		# Using BASH default ' \t\n'

    	case "$#" in
    	3)	case "$1" in
    		-of)	of=1 ; shift ;;
    		 * )	return 1 ;;
    		esac ;;
    	2)	: ;;		# Poor man's "continue"
    	*)	return 1 ;;
    	esac

    	# NOTE: the (ls) command is NOT quoted (")
    	T=( $(ls --inode --ignore-backups --almost-all --directory \
    	--full-time --color=none --time=status --sort=none \
    	--format=long $1) )

    	case $of in
    	# Assign T back to the array whose name was passed as $2
    		0) eval $2=\( \"\$\{T\[@\]\}\" \) ;;
    	# Write T into filename passed as $2
    		1) echo "${T[@]}" > "$2" ;;
    	esac
    	return 0
       }

    # # # # # Is that string a legal number? # # # # #
    #
    #	IsNumber "Var"
    # # # # # There has to be a better way, sigh...

    IsNumber()
    {
    	local -i int
    	if [ $# -eq 0 ]
    	then
    		return 1
    	else
    		(let int=$1)  2>/dev/null
    		return $?	# Exit status of the let thread
    	fi
    }

    # # # # # Index Filesystem Directory Information # # # # #
    #
    #	IndexList "Field-Array-Name" "Index-Array-Name"
    # or
    #	IndexList -if Field-Array-Filename Index-Array-Name
    #	IndexList -of Field-Array-Name Index-Array-Filename
    #	IndexList -if -of Field-Array-Filename Index-Array-Filename
    # # # # #

    : <<IndexListDoc
    Walk an array of directory fields produced by ListDirectory

    Having suppressed the line breaks in an otherwise line oriented
    report, build an index to the array element which starts each line.

    Each line gets two index entries, the first element of each line
    (inode) and the element that holds the pathname of the file.

    The first index entry pair (Line-Number==0) are informational:
    Index-Array-Name[0] : Number of "Lines" indexed
    Index-Array-Name[1] : "Current Line" pointer into Index-Array-Name

    The following index pairs (if any) hold element indexes into
    the Field-Array-Name per:
    Index-Array-Name[Line-Number * 2] : The "inode" field element.
    NOTE: This distance may be either +11 or +12 elements.
    Index-Array-Name[(Line-Number * 2) + 1] : The "pathname" element.
    NOTE: This distance may be a variable number of elements.
    Next line index pair for Line-Number+1.
    IndexListDoc

    IndexList()
    {
    	local -a LIST			# Local of listname passed
    	local -a -i INDEX=( 0 0 )	# Local of index to return
    	local -i Lidx Lcnt
    	local -i if=0 of=0		# Default to variable names

    	case "$#" in			# Simplistic option testing
    		0) return 1 ;;
    		1) return 1 ;;
    		2) : ;;			# Poor man's continue
    		3) case "$1" in
    			-if) if=1 ;;
    			-of) of=1 ;;
    			 * ) return 1 ;;
    		   esac ; shift ;;
    		4) if=1 ; of=1 ; shift ; shift ;;
    		*) return 1
    	esac

    	# Make local copy of list
    	case "$if" in
    		0) eval LIST=\( \"\$\{$1\[@\]\}\" \) ;;
    		1) LIST=( $(cat $1) ) ;;
    	esac

    	# Grok (grope?) the array
    	Lcnt=${#LIST[@]}
    	Lidx=0
    	until (( Lidx >= Lcnt ))
    	do
    	if IsNumber ${LIST[$Lidx]}
    	then
    		local -i inode name
    		local ft
    		inode=Lidx
    		local m=${LIST[$Lidx+2]}	# Hard Links field
    		ft=${LIST[$Lidx+1]:0:1} 	# Fast-Stat
    		case $ft in
    		b)	((Lidx+=12)) ;;		# Block device
    		c)	((Lidx+=12)) ;;		# Character device
    		*)	((Lidx+=11)) ;;		# Anything else
    		esac
    		name=Lidx
    		case $ft in
    		-)	((Lidx+=1)) ;;		# The easy one
    		b)	((Lidx+=1)) ;;		# Block device
    		c)	((Lidx+=1)) ;;		# Character device
    		d)	((Lidx+=1)) ;;		# The other easy one
    		l)	((Lidx+=3)) ;;		# At LEAST two more fields
    #  A little more elegance here would handle pipes,
    #+ sockets, deleted files - later.
    		*)	until IsNumber ${LIST[$Lidx]} || ((Lidx >= Lcnt))
    			do
    				((Lidx+=1))
    			done
    			;;			# Not required
    		esac
    		INDEX[${#INDEX[*]}]=$inode
    		INDEX[${#INDEX[*]}]=$name
    		INDEX[0]=${INDEX[0]}+1		# One more "line" found
    # echo "Line: ${INDEX[0]} Type: $ft Links: $m Inode: \
    # ${LIST[$inode]} Name: ${LIST[$name]}"

    	else
    		((Lidx+=1))
    	fi
    	done
    	case "$of" in
    		0) eval $2=\( \"\$\{INDEX\[@\]\}\" \) ;;
    		1) echo "${INDEX[@]}" > "$2" ;;
    	esac
    	return 0				# What could go wrong?
    }

    # # # # # Content Identify File # # # # #
    #
    #	DigestFile Input-Array-Name Digest-Array-Name
    # or
    #	DigestFile -if Input-FileName Digest-Array-Name
    # # # # #

    # Here document used as a comment block.
    : <<DigestFilesDoc

    The key (no pun intended) to a Unified Content File System (UCFS)
    is to distinguish the files in the system based on their content.
    Distinguishing files by their name is just so 20th Century.

    The content is distinguished by computing a checksum of that content.
    This version uses the md5sum program to generate a 128 bit checksum
    representative of the file's contents.
    There is a chance that two files having different content might
    generate the same checksum using md5sum (or any checksum).  Should
    that become a problem, then the use of md5sum can be replace by a
    cyrptographic signature.  But until then...

    The md5sum program is documented as outputting three fields (and it
    does), but when read it appears as two fields (array elements).  This
    is caused by the lack of whitespace between the second and third field.
    So this function gropes the md5sum output and returns:
    	[0]	32 character checksum in hexidecimal (UCFS filename)
    	[1]	Single character: ' ' text file, '*' binary file
    	[2]	Filesystem (20th Century Style) name
    	Note: That name may be the character '-' indicating STDIN read.

    DigestFilesDoc

    DigestFile()
    {
    	local if=0		# Default, variable name
    	local -a T1 T2

    	case "$#" in
    	3)	case "$1" in
    		-if)	if=1 ; shift ;;
    		 * )	return 1 ;;
    		esac ;;
    	2)	: ;;		# Poor man's "continue"
    	*)	return 1 ;;
    	esac

    	case $if in
    	0) eval T1=\( \"\$\{$1\[@\]\}\" \)
    	   T2=( $(echo ${T1[@]} | md5sum -) )
    	   ;;
    	1) T2=( $(md5sum $1) )
    	   ;;
    	esac

    	case ${#T2[@]} in
    	0) return 1 ;;
    	1) return 1 ;;
    	2) case ${T2[1]:0:1} in		# SanScrit-2.0.5
    	   \*) T2[${#T2[@]}]=${T2[1]:1}
    	       T2[1]=\*
    	       ;;
    	    *) T2[${#T2[@]}]=${T2[1]}
    	       T2[1]=" "
    	       ;;
    	   esac
    	   ;;
    	3) : ;; # Assume it worked
    	*) return 1 ;;
    	esac

    	local -i len=${#T2[0]}
    	if [ $len -ne 32 ] ; then return 1 ; fi
    	eval $2=\( \"\$\{T2\[@\]\}\" \)
    }

    # # # # # Locate File # # # # #
    #
    #	LocateFile [-l] FileName Location-Array-Name
    # or
    #	LocateFile [-l] -of FileName Location-Array-FileName
    # # # # #

    # A file location is Filesystem-id and inode-number

    # Here document used as a comment block.
    : <<StatFieldsDoc
    	Based on stat, version 2.2
    	stat -t and stat -lt fields
    	[0]	name
    	[1]	Total size
    		File - number of bytes
    		Symbolic link - string length of pathname
    	[2]	Number of (512 byte) blocks allocated
    	[3]	File type and Access rights (hex)
    	[4]	User ID of owner
    	[5]	Group ID of owner
    	[6]	Device number
    	[7]	Inode number
    	[8]	Number of hard links
    	[9]	Device type (if inode device) Major
    	[10]	Device type (if inode device) Minor
    	[11]	Time of last access
    		May be disabled in 'mount' with noatime
    		atime of files changed by exec, read, pipe, utime, mknod (mmap?)
    		atime of directories changed by addition/deletion of files
    	[12]	Time of last modification
    		mtime of files changed by write, truncate, utime, mknod
    		mtime of directories changed by addtition/deletion of files
    	[13]	Time of last change
    		ctime reflects time of changed inode information (owner, group
    		permissions, link count
    -*-*- Per:
    	Return code: 0
    	Size of array: 14
    	Contents of array
    	Element 0: /home/mszick
    	Element 1: 4096
    	Element 2: 8
    	Element 3: 41e8
    	Element 4: 500
    	Element 5: 500
    	Element 6: 303
    	Element 7: 32385
    	Element 8: 22
    	Element 9: 0
    	Element 10: 0
    	Element 11: 1051221030
    	Element 12: 1051214068
    	Element 13: 1051214068

    	For a link in the form of linkname -> realname
    	stat -t  linkname returns the linkname (link) information
    	stat -lt linkname returns the realname information

    	stat -tf and stat -ltf fields
    	[0]	name
    	[1]	ID-0?		# Maybe someday, but Linux stat structure
    	[2]	ID-0?		# does not have either LABEL nor UUID
    				# fields, currently information must come
    				# from file-system specific utilities
    	These will be munged into:
    	[1]	UUID if possible
    	[2]	Volume Label if possible
    	Note: 'mount -l' does return the label and could return the UUID

    	[3]	Maximum length of filenames
    	[4]	Filesystem type
    	[5]	Total blocks in the filesystem
    	[6]	Free blocks
    	[7]	Free blocks for non-root user(s)
    	[8]	Block size of the filesystem
    	[9]	Total inodes
    	[10]	Free inodes

    -*-*- Per:
    	Return code: 0
    	Size of array: 11
    	Contents of array
    	Element 0: /home/mszick
    	Element 1: 0
    	Element 2: 0
    	Element 3: 255
    	Element 4: ef53
    	Element 5: 2581445
    	Element 6: 2277180
    	Element 7: 2146050
    	Element 8: 4096
    	Element 9: 1311552
    	Element 10: 1276425

    StatFieldsDoc

    #	LocateFile [-l] FileName Location-Array-Name
    #	LocateFile [-l] -of FileName Location-Array-FileName

    LocateFile()
    {
    	local -a LOC LOC1 LOC2
    	local lk="" of=0

    	case "$#" in
    	0) return 1 ;;
    	1) return 1 ;;
    	2) : ;;
    	*) while (( "$#" > 2 ))
    	   do
    	      case "$1" in
    	       -l) lk=-1 ;;
    	      -of) of=1 ;;
    	        *) return 1 ;;
    	      esac
    	   shift
               done ;;
    	esac

    # More Sanscrit-2.0.5
          # LOC1=( $(stat -t $lk $1) )
          # LOC2=( $(stat -tf $lk $1) )
          # Uncomment above two lines if system has "stat" command installed.
    	LOC=( ${LOC1[@]:0:1} ${LOC1[@]:3:11}
    	      ${LOC2[@]:1:2} ${LOC2[@]:4:1} )

    	case "$of" in
    		0) eval $2=\( \"\$\{LOC\[@\]\}\" \) ;;
    		1) echo "${LOC[@]}" > "$2" ;;
    	esac
    	return 0
    # Which yields (if you are lucky, and have "stat" installed)
    # -*-*- Location Discriptor -*-*-
    #	Return code: 0
    #	Size of array: 15
    #	Contents of array
    #	Element 0: /home/mszick		20th Century name
    #	Element 1: 41e8			Type and Permissions
    #	Element 2: 500			User
    #	Element 3: 500			Group
    #	Element 4: 303			Device
    #	Element 5: 32385		inode
    #	Element 6: 22			Link count
    #	Element 7: 0			Device Major
    #	Element 8: 0			Device Minor
    #	Element 9: 1051224608		Last Access
    #	Element 10: 1051214068		Last Modify
    #	Element 11: 1051214068		Last Status
    #	Element 12: 0			UUID (to be)
    #	Element 13: 0			Volume Label (to be)
    #	Element 14: ef53		Filesystem type
    }

    # And then there was some test code

    ListArray() # ListArray Name
    {
    	local -a Ta

    	eval Ta=\( \"\$\{$1\[@\]\}\" \)
    	echo
    	echo "-*-*- List of Array -*-*-"
    	echo "Size of array $1: ${#Ta[*]}"
    	echo "Contents of array $1:"
    	for (( i=0 ; i<${#Ta[*]} ; i++ ))
    	do
    	    echo -e "\tElement $i: ${Ta[$i]}"
    	done
    	return 0
    }

    declare -a CUR_DIR
    # For small arrays
    ListDirectory "${PWD}" CUR_DIR
    ListArray CUR_DIR

    declare -a DIR_DIG
    DigestFile CUR_DIR DIR_DIG
    echo "The new \"name\" (checksum) for ${CUR_DIR[9]} is ${DIR_DIG[0]}"

    declare -a DIR_ENT
    # BIG_DIR # For really big arrays - use a temporary file in ramdisk
    # BIG-DIR # ListDirectory -of "${CUR_DIR[11]}/*" "/tmpfs/junk2"
    ListDirectory "${CUR_DIR[11]}/*" DIR_ENT

    declare -a DIR_IDX
    # BIG-DIR # IndexList -if "/tmpfs/junk2" DIR_IDX
    IndexList DIR_ENT DIR_IDX

    declare -a IDX_DIG
    # BIG-DIR # DIR_ENT=( $(cat /tmpfs/junk2) )
    # BIG-DIR # DigestFile -if /tmpfs/junk2 IDX_DIG
    DigestFile DIR_ENT IDX_DIG
    # Small (should) be able to parallize IndexList & DigestFile
    # Large (should) be able to parallize IndexList & DigestFile & the assignment
    echo "The \"name\" (checksum) for the contents of ${PWD} is ${IDX_DIG[0]}"

    declare -a FILE_LOC
    LocateFile ${PWD} FILE_LOC
    ListArray FILE_LOC

    exit 0

Stéphane Chazelas demonstrates object-oriented programming in a Bash script.

Mariusz Gniazdowski contributed a hash library for use in scripts.

Example A-20. Library of hash functions

    # Hash:
    # Hash function library
    # Author: Mariusz Gniazdowski <mariusz.gn-at-gmail.com>
    # Date: 2005-04-07

    # Functions making emulating hashes in Bash a little less painful.

    #    Limitations:
    #  * Only global variables are supported.
    #  * Each hash instance generates one global variable per value.
    #  * Variable names collisions are possible
    #+   if you define variable like __hash__hashname_key
    #  * Keys must use chars that can be part of a Bash variable name
    #+   (no dashes, periods, etc.).
    #  * The hash is created as a variable:
    #    ... hashname_keyname
    #    So if somone will create hashes like:
    #      myhash_ + mykey = myhash__mykey
    #      myhash + _mykey = myhash__mykey
    #    Then there will be a collision.
    #    (This should not pose a major problem.)

    Hash_config_varname_prefix=__hash__

    # Emulates:  hash[key]=value
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3 - value
    function hash_set {
    	eval "${Hash_config_varname_prefix}${1}_${2}=\"${3}\""
    }

    # Emulates:  value=hash[key]
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3 - value (name of global variable to set)
    function hash_get_into {
    	eval "$3=\"\$${Hash_config_varname_prefix}${1}_${2}\""
    }

    # Emulates:  echo hash[key]
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3 - echo params (like -n, for example)
    function hash_echo {
    	eval "echo $3 \"\$${Hash_config_varname_prefix}${1}_${2}\""
    }

    # Emulates:  hash1[key1]=hash2[key2]
    #
    # Params:
    # 1 - hash1
    # 2 - key1
    # 3 - hash2
    # 4 - key2
    function hash_copy {
    eval "${Hash_config_varname_prefix}${1}_${2}\
    =\"\$${Hash_config_varname_prefix}${3}_${4}\""
    }

    # Emulates:  hash[keyN-1]=hash[key2]=...hash[key1]
    #
    # Copies first key to rest of keys.
    #
    # Params:
    # 1 - hash1
    # 2 - key1
    # 3 - key2
    # . . .
    # N - keyN
    function hash_dup {
      local hashName="$1" keyName="$2"
      shift 2
      until [ ${#} -le 0 ]; do
        eval "${Hash_config_varname_prefix}${hashName}_${1}\
    =\"\$${Hash_config_varname_prefix}${hashName}_${keyName}\""
      shift;
      done;
    }

    # Emulates:  unset hash[key]
    #
    # Params:
    # 1 - hash
    # 2 - key
    function hash_unset {
    	eval "unset ${Hash_config_varname_prefix}${1}_${2}"
    }

    # Emulates something similar to:  ref=&hash[key]
    #
    # The reference is name of the variable in which value is held.
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3 - ref - Name of global variable to set.
    function hash_get_ref_into {
    	eval "$3=\"${Hash_config_varname_prefix}${1}_${2}\""
    }

    # Emulates something similar to:  echo &hash[key]
    #
    # That reference is name of variable in which value is held.
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3 - echo params (like -n for example)
    function hash_echo_ref {
    	eval "echo $3 \"${Hash_config_varname_prefix}${1}_${2}\""
    }

    # Emulates something similar to:  $$hash[key](param1, param2, ...)
    #
    # Params:
    # 1 - hash
    # 2 - key
    # 3,4, ... - Function parameters
    function hash_call {
      local hash key
      hash=$1
      key=$2
      shift 2
      eval "eval \"\$${Hash_config_varname_prefix}${hash}_${key} \\\"\\\$@\\\"\""
    }

    # Emulates something similar to:  isset(hash[key]) or hash[key]==NULL
    #
    # Params:
    # 1 - hash
    # 2 - key
    # Returns:
    # 0 - there is such key
    # 1 - there is no such key
    function hash_is_set {
      eval "if [[ \"\${${Hash_config_varname_prefix}${1}_${2}-a}\" = \"a\" &&
      \"\${${Hash_config_varname_prefix}${1}_${2}-b}\" = \"b\" ]]
        then return 1; else return 0; fi"
    }

    # Emulates something similar to:
    #   foreach($hash as $key => $value) { fun($key,$value); }
    #
    # It is possible to write different variations of this function.
    # Here we use a function call to make it as "generic" as possible.
    #
    # Params:
    # 1 - hash
    # 2 - function name
    function hash_foreach {
      local keyname oldIFS="$IFS"
      IFS=' '
      for i in $(eval "echo \${!${Hash_config_varname_prefix}${1}_*}"); do
        keyname=$(eval "echo \${i##${Hash_config_varname_prefix}${1}_}")
        eval "$2 $keyname \"\$$i\""
      done
    IFS="$oldIFS"
    }

    #  NOTE: In lines 103 and 116, ampersand changed.
    #  But, it doesn't matter, because these are comment lines anyhow.

Here is an example script using the foregoing hash library.

Example A-21. Colorizing text using hash functions

    #!/bin/bash
    # hash-example.sh: Colorizing text.
    # Author: Mariusz Gniazdowski <mariusz.gn-at-gmail.com>

    . Hash.lib      # Load the library of functions.

    hash_set colors red          "\033[0;31m"
    hash_set colors blue         "\033[0;34m"
    hash_set colors light_blue   "\033[1;34m"
    hash_set colors light_red    "\033[1;31m"
    hash_set colors cyan         "\033[0;36m"
    hash_set colors light_green  "\033[1;32m"
    hash_set colors light_gray   "\033[0;37m"
    hash_set colors green        "\033[0;32m"
    hash_set colors yellow       "\033[1;33m"
    hash_set colors light_purple "\033[1;35m"
    hash_set colors purple       "\033[0;35m"
    hash_set colors reset_color  "\033[0;00m"

    # $1 - keyname
    # $2 - value
    try_colors() {
    	echo -en "$2"
    	echo "This line is $1."
    }
    hash_foreach colors try_colors
    hash_echo colors reset_color -en

    echo -e '\nLet us overwrite some colors with yellow.\n'
    # It's hard to read yellow text on some terminals.
    hash_dup colors yellow   red light_green blue green light_gray cyan
    hash_foreach colors try_colors
    hash_echo colors reset_color -en

    echo -e '\nLet us delete them and try colors once more . . .\n'

    for i in red light_green blue green light_gray cyan; do
    	hash_unset colors $i
    done
    hash_foreach colors try_colors
    hash_echo colors reset_color -en

    hash_set other txt "Other examples . . ."
    hash_echo other txt
    hash_get_into other txt text
    echo $text

    hash_set other my_fun try_colors
    hash_call other my_fun   purple "`hash_echo colors purple`"
    hash_echo colors reset_color -en

    echo; echo "Back to normal?"; echo

    exit $?

    #  On some terminals, the "light" colors print in bold,
    #  and end up looking darker than the normal ones.
    #  Why is this?

An example illustrating the mechanics of hashing, but from a different point of view.

Example A-22. More on hash functions

    #!/bin/bash
    # $Id: ha.sh,v 1.2 2005/04/21 23:24:26 oliver Exp $
    # Copyright 2005 Oliver Beckstein
    # Released under the GNU Public License
    # Author of script granted permission for inclusion in ABS Guide.
    # (Thank you!)

    #----------------------------------------------------------------
    # pseudo hash based on indirect parameter expansion
    # API: access through functions:
    #
    # create the hash:
    #
    #      newhash Lovers
    #
    # add entries (note single quotes for spaces)
    #
    #      addhash Lovers Tristan Isolde
    #      addhash Lovers 'Romeo Montague' 'Juliet Capulet'
    #
    # access value by key
    #
    #      gethash Lovers Tristan   ---->  Isolde
    #
    # show all keys
    #
    #      keyshash Lovers         ----> 'Tristan'  'Romeo Montague'
    #
    #
    # Convention: instead of perls' foo{bar} = boing' syntax,
    # use
    #       '_foo_bar=boing' (two underscores, no spaces)
    #
    # 1) store key   in _NAME_keys[]
    # 2) store value in _NAME_values[] using the same integer index
    # The integer index for the last entry is _NAME_ptr
    #
    # NOTE: No error or sanity checks, just bare bones.

    function _inihash () {
        # private function
        # call at the beginning of each procedure
        # defines: _keys _values _ptr
        #
        # Usage: _inihash NAME
        local name=$1
        _keys=_${name}_keys
        _values=_${name}_values
        _ptr=_${name}_ptr
    }

    function newhash () {
        # Usage: newhash NAME
        #        NAME should not contain spaces or dots.
        #        Actually: it must be a legal name for a Bash variable.
        # We rely on Bash automatically recognising arrays.
        local name=$1
        local _keys _values _ptr
        _inihash ${name}
        eval ${_ptr}=0
    }

    function addhash () {
        # Usage: addhash NAME KEY 'VALUE with spaces'
        #        arguments with spaces need to be quoted with single quotes ''
        local name=$1 k="$2" v="$3"
        local _keys _values _ptr
        _inihash ${name}

        #echo "DEBUG(addhash): ${_ptr}=${!_ptr}"

        eval let ${_ptr}=${_ptr}+1
        eval "$_keys[${!_ptr}]=\"${k}\""
        eval "$_values[${!_ptr}]=\"${v}\""
    }

    function gethash () {
        #  Usage: gethash NAME KEY
        #         Returns boing
        #         ERR=0 if entry found, 1 otherwise
        #  That's not a proper hash --
        #+ we simply linearly search through the keys.
        local name=$1 key="$2"
        local _keys _values _ptr
        local k v i found h
        _inihash ${name}

        # _ptr holds the highest index in the hash
        found=0

        for i in $(seq 1 ${!_ptr}); do
    	h="\${${_keys}[${i}]}"  #  Safer to do it in two steps,
    	eval k=${h}             #+ especially when quoting for spaces.
    	if [ "${k}" = "${key}" ]; then found=1; break; fi
        done;

        [ ${found} = 0 ] && return 1;
        # else: i is the index that matches the key
        h="\${${_values}[${i}]}"
        eval echo "${h}"
        return 0;
    }

    function keyshash () {
        # Usage: keyshash NAME
        # Returns list of all keys defined for hash name.
        local name=$1 key="$2"
        local _keys _values _ptr
        local k i h
        _inihash ${name}

        # _ptr holds the highest index in the hash
        for i in $(seq 1 ${!_ptr}); do
    	h="\${${_keys}[${i}]}"   #  Safer to do it in two steps,
    	eval k=${h}              #+ especially when quoting for spaces.
    	echo -n "'${k}' "
        done;
    }

    # -----------------------------------------------------------------------

    # Now, let's test it.
    # (Per comments at the beginning of the script.)
    newhash Lovers
    addhash Lovers Tristan Isolde
    addhash Lovers 'Romeo Montague' 'Juliet Capulet'

    # Output results.
    echo
    gethash Lovers Tristan      # Isolde
    echo
    keyshash Lovers             # 'Tristan' 'Romeo Montague'
    echo; echo

    exit 0

    # Exercise:
    # --------

    # Add error checks to the functions.

Now for a script that installs and mounts those cute USB keychain solid-state "hard drives."

Example A-23. Mounting USB keychain storage devices

    #!/bin/bash
    # ==> usb.sh
    # ==> Script for mounting and installing pen/keychain USB storage devices.
    # ==> Runs as root at system startup (see below).
    # ==>
    # ==> Newer Linux distros (2004 or later) autodetect
    # ==> and install USB pen drives, and therefore don't need this script.
    # ==> But, it's still instructive.

    #  This code is free software covered by GNU GPL license version 2 or above.
    #  Please refer to http://www.gnu.org/ for the full license text.
    #
    #  Some code lifted from usb-mount by Michael Hamilton's usb-mount (LGPL)
    #+ see http://users.actrix.co.nz/michael/usbmount.html
    #
    #  INSTALL
    #  -------
    #  Put this in /etc/hotplug/usb/diskonkey.
    #  Then look in /etc/hotplug/usb.distmap, and copy all usb-storage entries
    #+ into /etc/hotplug/usb.usermap, substituting "usb-storage" for "diskonkey".
    #  Otherwise this code is only run during the kernel module invocation/removal
    #+ (at least in my tests), which defeats the purpose.
    #
    #  TODO
    #  ----
    #  Handle more than one diskonkey device at one time (e.g. /dev/diskonkey1
    #+ and /mnt/diskonkey1), etc. The biggest problem here is the handling in
    #+ devlabel, which I haven't yet tried.
    #
    #  AUTHOR and SUPPORT
    #  ------------------
    #  Konstantin Riabitsev, <icon linux duke edu>.
    #  Send any problem reports to my email address at the moment.
    #
    # ==> Comments added by ABS Guide author.

    SYMLINKDEV=/dev/diskonkey
    MOUNTPOINT=/mnt/diskonkey
    DEVLABEL=/sbin/devlabel
    DEVLABELCONFIG=/etc/sysconfig/devlabel
    IAM=$0

    ##
    # Functions lifted near-verbatim from usb-mount code.
    #
    function allAttachedScsiUsb {
      find /proc/scsi/ -path '/proc/scsi/usb-storage*' -type f |
      xargs grep -l 'Attached: Yes'
    }
    function scsiDevFromScsiUsb {
      echo $1 | awk -F"[-/]" '{ n=$(NF-1);
      print "/dev/sd" substr("abcdefghijklmnopqrstuvwxyz", n+1, 1) }'
    }

    if [ "${ACTION}" = "add" ] && [ -f "${DEVICE}" ]; then
        ##
        # lifted from usbcam code.
        #
        if [ -f /var/run/console.lock ]; then
            CONSOLEOWNER=`cat /var/run/console.lock`
        elif [ -f /var/lock/console.lock ]; then
            CONSOLEOWNER=`cat /var/lock/console.lock`
        else
            CONSOLEOWNER=
        fi
        for procEntry in $(allAttachedScsiUsb); do
            scsiDev=$(scsiDevFromScsiUsb $procEntry)
            #  Some bug with usb-storage?
            #  Partitions are not in /proc/partitions until they are accessed
            #+ somehow.
            /sbin/fdisk -l $scsiDev >/dev/null
            ##
            #  Most devices have partitioning info, so the data would be on
            #+ /dev/sd?1. However, some stupider ones don't have any partitioning
            #+ and use the entire device for data storage. This tries to
            #+ guess semi-intelligently if we have a /dev/sd?1 and if not, then
            #+ it uses the entire device and hopes for the better.
            #
            if grep -q `basename $scsiDev`1 /proc/partitions; then
                part="$scsiDev""1"
            else
                part=$scsiDev
            fi
            ##
            #  Change ownership of the partition to the console user so they can
            #+ mount it.
            #
            if [ ! -z "$CONSOLEOWNER" ]; then
                chown $CONSOLEOWNER:disk $part
            fi
            ##
            # This checks if we already have this UUID defined with devlabel.
            # If not, it then adds the device to the list.
            #
            prodid=`$DEVLABEL printid -d $part`
            if ! grep -q $prodid $DEVLABELCONFIG; then
                # cross our fingers and hope it works
                $DEVLABEL add -d $part -s $SYMLINKDEV 2>/dev/null
            fi
            ##
            # Check if the mount point exists and create if it doesn't.
            #
            if [ ! -e $MOUNTPOINT ]; then
                mkdir -p $MOUNTPOINT
            fi
            ##
            # Take care of /etc/fstab so mounting is easy.
            #
            if ! grep -q "^$SYMLINKDEV" /etc/fstab; then
                # Add an fstab entry
                echo -e \
                    "$SYMLINKDEV\t\t$MOUNTPOINT\t\tauto\tnoauto,owner,kudzu 0 0" \
                    >> /etc/fstab
            fi
        done
        if [ ! -z "$REMOVER" ]; then
            ##
            # Make sure this script is triggered on device removal.
            #
            mkdir -p `dirname $REMOVER`
            ln -s $IAM $REMOVER
        fi
    elif [ "${ACTION}" = "remove" ]; then
        ##
        # If the device is mounted, unmount it cleanly.
        #
        if grep -q "$MOUNTPOINT" /etc/mtab; then
            # unmount cleanly
            umount -l $MOUNTPOINT
        fi
        ##
        # Remove it from /etc/fstab if it's there.
        #
        if grep -q "^$SYMLINKDEV" /etc/fstab; then
            grep -v "^$SYMLINKDEV" /etc/fstab > /etc/.fstab.new
            mv -f /etc/.fstab.new /etc/fstab
        fi
    fi

    exit 0

Converting a text file to HTML format.

Example A-24. Converting to HTML

    #!/bin/bash
    # tohtml.sh [v. 0.2, reldate: 06/26/08, still buggy]

    # Convert a text file to HTML format.
    # Author: Mendel Cooper
    # License: GPL3
    # Usage: sh tohtml.sh < textfile > htmlfile
    # Script can easily be modified to accept source and target filenames.

    #    Assumptions:
    # 1) Paragraphs in (target) text file are separated by a blank line.
    # 2) Jpeg images (*.jpg) are located in "images" subdirectory.
    #    In the target file, the image names are enclosed in square brackets,
    #    for example, [image01.jpg].
    # 3) Emphasized (italic) phrases begin with a space+underscore
    #+   or the first character on the line is an underscore,
    #+   and end with an underscore+space or underscore+end-of-line.

    # Settings
    FNTSIZE=2        # Small-medium font size
    IMGDIR="images"  # Image directory
    # Headers
    HDR01='<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">'
    HDR02='<!-- Converted to HTML by ***tohtml.sh*** script -->'
    HDR03='<!-- script author: M. Leo Cooper <thegrendel.abs@gmail.com> -->'
    HDR10='<html>'
    HDR11='<head>'
    HDR11a='</head>'
    HDR12a='<title>'
    HDR12b='</title>'
    HDR121='<META NAME="GENERATOR" CONTENT="tohtml.sh script">'
    HDR13='<body bgcolor="#dddddd">'   # Change background color to suit.
    HDR14a='<font size='
    HDR14b='>'
    # Footers
    FTR10='</body>'
    FTR11='</html>'
    # Tags
    BOLD="<b>"
    CENTER="<center>"
    END_CENTER="</center>"
    LF="<br>"

    write_headers ()
      {
      echo "$HDR01"
      echo
      echo "$HDR02"
      echo "$HDR03"
      echo
      echo
      echo "$HDR10"
      echo "$HDR11"
      echo "$HDR121"
      echo "$HDR11a"
      echo "$HDR13"
      echo
      echo -n "$HDR14a"
      echo -n "$FNTSIZE"
      echo "$HDR14b"
      echo
      echo "$BOLD"        # Everything in bold (more easily readable).
      }

    process_text ()
      {
      while read line     # Read one line at a time.
      do
        {
        if [ ! "$line" ]  # Blank line?
        then              # Then new paragraph must follow.
          echo
          echo "$LF"      # Insert two <br> tags.
          echo "$LF"
          echo
          continue        # Skip the underscore test.
        else              # Otherwise . . .

          if [[ "$line" =~ "\[*jpg\]" ]]  # Is a graphic?
          then                            # Strip away brackets.
            temp=$( echo "$line" | sed -e 's/\[//' -e 's/\]//' )
            line=""$CENTER" <img src="\"$IMGDIR"/$temp\"> "$END_CENTER" "
                                          # Add image tag.
                                          # And, center it.
          fi

        fi

        echo "$line" | grep -q _
        if [ "$?" -eq 0 ]    # If line contains underscore ...
        then
          # ===================================================
          # Convert underscored phrase to italics.
          temp=$( echo "$line" |
                  sed -e 's/ _/ <i>/' -e 's/_/<\/i> /' |
                  sed -e 's/^_/<i>/'  -e 's/_/<\/i>/' )
          #  Process only underscores prefixed by space,
          #+ or at beginning or end of line.
          #  Do not convert underscores embedded within a word!
          line="$temp"
          # Slows script execution. Can be optimized?
          # ===================================================
        fi

        echo
        echo "$line"
        echo
        } # End while
      done
      }   # End process_text ()

    write_footers ()  # Termination tags.
      {
      echo "$FTR10"
      echo "$FTR11"
      }

    # main () {
    # =========
    write_headers
    process_text
    write_footers
    # =========
    #         }

    exit $?

    #  Exercises:
    #  ---------
    #  1) Fixup: Check for closing underscore before a comma or period.
    #  2) Add a test for the presence of a closing underscore
    #+    in phrases to be italicized.

Here is something to warm the hearts of webmasters and mistresses: a script that saves weblogs.

Example A-25. Preserving weblogs

    #!/bin/bash
    # archiveweblogs.sh v1.0

    # Troy Engel <tengel@fluid.com>
    # Slightly modified by document author.
    # Used with permission.
    #
    #  This script will preserve the normally rotated and
    #+ thrown away weblogs from a default RedHat/Apache installation.
    #  It will save the files with a date/time stamp in the filename,
    #+ bzipped, to a given directory.
    #
    #  Run this from crontab nightly at an off hour,
    #+ as bzip2 can suck up some serious CPU on huge logs:
    #  0 2 * * * /opt/sbin/archiveweblogs.sh

    PROBLEM=66

    # Set this to your backup dir.
    BKP_DIR=/opt/backups/weblogs

    # Default Apache/RedHat stuff
    LOG_DAYS="4 3 2 1"
    LOG_DIR=/var/log/httpd
    LOG_FILES="access_log error_log"

    # Default RedHat program locations
    LS=/bin/ls
    MV=/bin/mv
    ID=/usr/bin/id
    CUT=/bin/cut
    COL=/usr/bin/column
    BZ2=/usr/bin/bzip2

    # Are we root?
    USER=`$ID -u`
    if [ "X$USER" != "X0" ]; then
      echo "PANIC: Only root can run this script!"
      exit $PROBLEM
    fi

    # Backup dir exists/writable?
    if [ ! -x $BKP_DIR ]; then
      echo "PANIC: $BKP_DIR doesn't exist or isn't writable!"
      exit $PROBLEM
    fi

    # Move, rename and bzip2 the logs
    for logday in $LOG_DAYS; do
      for logfile in $LOG_FILES; do
        MYFILE="$LOG_DIR/$logfile.$logday"
        if [ -w $MYFILE ]; then
          DTS=`$LS -lgo --time-style=+%Y%m%d $MYFILE | $COL -t | $CUT -d ' ' -f7`
          $MV $MYFILE $BKP_DIR/$logfile.$DTS
          $BZ2 $BKP_DIR/$logfile.$DTS
        else
          # Only spew an error if the file exits (ergo non-writable).
          if [ -f $MYFILE ]; then
            echo "ERROR: $MYFILE not writable. Skipping."
          fi
        fi
      done
    done

    exit 0

How to keep the shell from expanding and reinterpreting text strings.

Example A-26. Protecting literal strings

    #! /bin/bash
    # protect_literal.sh

    # set -vx

    :<<-'_Protect_Literal_String_Doc'

        Copyright (c) Michael S. Zick, 2003; All Rights Reserved
        License: Unrestricted reuse in any form, for any purpose.
        Warranty: None
        Revision: $ID$

        Documentation redirected to the Bash no-operation.
        Bash will '/dev/null' this block when the script is first read.
        (Uncomment the above set command to see this action.)

        Remove the first (Sha-Bang) line when sourcing this as a library
        procedure.  Also comment out the example use code in the two
        places where shown.

        Usage:
            _protect_literal_str 'Whatever string meets your ${fancy}'
            Just echos the argument to standard out, hard quotes
            restored.

            $(_protect_literal_str 'Whatever string meets your ${fancy}')
            as the right-hand-side of an assignment statement.

        Does:
            As the right-hand-side of an assignment, preserves the
            hard quotes protecting the contents of the literal during
            assignment.

        Notes:
            The strange names (_*) are used to avoid trampling on
            the user's chosen names when this is sourced as a
            library.

    _Protect_Literal_String_Doc

    # The 'for illustration' function form

    _protect_literal_str() {

    # Pick an un-used, non-printing character as local IFS.
    # Not required, but shows that we are ignoring it.
        local IFS=$'\x1B'               # \ESC character

    # Enclose the All-Elements-Of in hard quotes during assignment.
        local tmp=$'\x27'$@$'\x27'
    #    local tmp=$'\''$@$'\''         # Even uglier.

        local len=${#tmp}               # Info only.
        echo $tmp is $len long.         # Output AND information.
    }

    # This is the short-named version.
    _pls() {
        local IFS=$'x1B'                # \ESC character (not required)
        echo $'\x27'$@$'\x27'           # Hard quoted parameter glob
    }

    # :<<-'_Protect_Literal_String_Test'
    # # # Remove the above "# " to disable this code. # # #

    # See how that looks when printed.
    echo
    echo "- - Test One - -"
    _protect_literal_str 'Hello $user'
    _protect_literal_str 'Hello "${username}"'
    echo

    # Which yields:
    # - - Test One - -
    # 'Hello $user' is 13 long.
    # 'Hello "${username}"' is 21 long.

    #  Looks as expected, but why all of the trouble?
    #  The difference is hidden inside the Bash internal order
    #+ of operations.
    #  Which shows when you use it on the RHS of an assignment.

    # Declare an array for test values.
    declare -a arrayZ

    # Assign elements with various types of quotes and escapes.
    arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )

    # Now list that array and see what is there.
    echo "- - Test Two - -"
    for (( i=0 ; i<${#arrayZ[*]} ; i++ ))
    do
        echo  Element $i: ${arrayZ[$i]} is: ${#arrayZ[$i]} long.
    done
    echo

    # Which yields:
    # - - Test Two - -
    # Element 0: zero is: 4 long.           # Our marker element
    # Element 1: 'Hello ${Me}' is: 13 long. # Our "$(_pls '...' )"
    # Element 2: Hello ${You} is: 12 long.  # Quotes are missing
    # Element 3: \'Pass: \' is: 10 long.    # ${pw} expanded to nothing

    # Now make an assignment with that result.
    declare -a array2=( ${arrayZ[@]} )

    # And print what happened.
    echo "- - Test Three - -"
    for (( i=0 ; i<${#array2[*]} ; i++ ))
    do
        echo  Element $i: ${array2[$i]} is: ${#array2[$i]} long.
    done
    echo

    # Which yields:
    # - - Test Three - -
    # Element 0: zero is: 4 long.           # Our marker element.
    # Element 1: Hello ${Me} is: 11 long.   # Intended result.
    # Element 2: Hello is: 5 long.          # ${You} expanded to nothing.
    # Element 3: 'Pass: is: 6 long.         # Split on the whitespace.
    # Element 4: ' is: 1 long.              # The end quote is here now.

    #  Our Element 1 has had its leading and trailing hard quotes stripped.
    #  Although not shown, leading and trailing whitespace is also stripped.
    #  Now that the string contents are set, Bash will always, internally,
    #+ hard quote the contents as required during its operations.

    #  Why?
    #  Considering our "$(_pls 'Hello ${Me}')" construction:
    #  " ... " -> Expansion required, strip the quotes.
    #  $( ... ) -> Replace with the result of..., strip this.
    #  _pls ' ... ' -> called with literal arguments, strip the quotes.
    #  The result returned includes hard quotes; BUT the above processing
    #+ has already been done, so they become part of the value assigned.
    #
    #  Similarly, during further usage of the string variable, the ${Me}
    #+ is part of the contents (result) and survives any operations
    #  (Until explicitly told to evaluate the string).

    #  Hint: See what happens when the hard quotes ($'\x27') are replaced
    #+ with soft quotes ($'\x22') in the above procedures.
    #  Interesting also is to remove the addition of any quoting.

    # _Protect_Literal_String_Test
    # # # Remove the above "# " to disable this code. # # #

    exit 0

But, what if you want the shell to expand and reinterpret strings?

Example A-27. Unprotecting literal strings

    #! /bin/bash
    # unprotect_literal.sh

    # set -vx

    :<<-'_UnProtect_Literal_String_Doc'

        Copyright (c) Michael S. Zick, 2003; All Rights Reserved
        License: Unrestricted reuse in any form, for any purpose.
        Warranty: None
        Revision: $ID$

        Documentation redirected to the Bash no-operation. Bash will
        '/dev/null' this block when the script is first read.
        (Uncomment the above set command to see this action.)

        Remove the first (Sha-Bang) line when sourcing this as a library
        procedure.  Also comment out the example use code in the two
        places where shown.

        Usage:
            Complement of the "$(_pls 'Literal String')" function.
            (See the protect_literal.sh example.)

            StringVar=$(_upls ProtectedSringVariable)

        Does:
            When used on the right-hand-side of an assignment statement;
            makes the substitions embedded in the protected string.

        Notes:
            The strange names (_*) are used to avoid trampling on
            the user's chosen names when this is sourced as a
            library.

    _UnProtect_Literal_String_Doc

    _upls() {
        local IFS=$'x1B'                # \ESC character (not required)
        eval echo $@                    # Substitution on the glob.
    }

    # :<<-'_UnProtect_Literal_String_Test'
    # # # Remove the above "# " to disable this code. # # #

    _pls() {
        local IFS=$'x1B'                # \ESC character (not required)
        echo $'\x27'$@$'\x27'           # Hard quoted parameter glob
    }

    # Declare an array for test values.
    declare -a arrayZ

    # Assign elements with various types of quotes and escapes.
    arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )

    # Now make an assignment with that result.
    declare -a array2=( ${arrayZ[@]} )

    # Which yielded:
    # - - Test Three - -
    # Element 0: zero is: 4 long            # Our marker element.
    # Element 1: Hello ${Me} is: 11 long    # Intended result.
    # Element 2: Hello is: 5 long           # ${You} expanded to nothing.
    # Element 3: 'Pass: is: 6 long          # Split on the whitespace.
    # Element 4: ' is: 1 long               # The end quote is here now.

    # set -vx

    #  Initialize 'Me' to something for the embedded ${Me} substitution.
    #  This needs to be done ONLY just prior to evaluating the
    #+ protected string.
    #  (This is why it was protected to begin with.)

    Me="to the array guy."

    # Set a string variable destination to the result.
    newVar=$(_upls ${array2[1]})

    # Show what the contents are.
    echo $newVar

    # Do we really need a function to do this?
    newerVar=$(eval echo ${array2[1]})
    echo $newerVar

    #  I guess not, but the _upls function gives us a place to hang
    #+ the documentation on.
    #  This helps when we forget what a # construction like:
    #+ $(eval echo ... ) means.

    # What if Me isn't set when the protected string is evaluated?
    unset Me
    newestVar=$(_upls ${array2[1]})
    echo $newestVar

    # Just gone, no hints, no runs, no errors.

    #  Why in the world?
    #  Setting the contents of a string variable containing character
    #+ sequences that have a meaning in Bash is a general problem in
    #+ script programming.
    #
    #  This problem is now solved in eight lines of code
    #+ (and four pages of description).

    #  Where is all this going?
    #  Dynamic content Web pages as an array of Bash strings.
    #  Content set per request by a Bash 'eval' command
    #+ on the stored page template.
    #  Not intended to replace PHP, just an interesting thing to do.
    ###
    #  Don't have a webserver application?
    #  No problem, check the example directory of the Bash source;
    #+ there is a Bash script for that also.

    # _UnProtect_Literal_String_Test
    # # # Remove the above "# " to disable this code. # # #

    exit 0

This interesting script helps hunt down spammers.

Example A-28. Spammer Identification

    #!/bin/bash

    # $Id: is_spammer.bash,v 1.12.2.11 2004/10/01 21:42:33 mszick Exp $
    # Above line is RCS info.

    # The latest version of this script is available from http://www.morethan.org.
    #
    # Spammer-identification
    # by Michael S. Zick
    # Used in the ABS Guide with permission.

    #######################################################
    # Documentation
    # See also "Quickstart" at end of script.
    #######################################################

    :<<-'__is_spammer_Doc_'

        Copyright (c) Michael S. Zick, 2004
        License: Unrestricted reuse in any form, for any purpose.
        Warranty: None -{Its a script; the user is on their own.}-

    Impatient?
        Application code: goto "# # # Hunt the Spammer' program code # # #"
        Example output: ":<<-'_is_spammer_outputs_'"
        How to use: Enter script name without arguments.
                    Or goto "Quickstart" at end of script.

    Provides
        Given a domain name or IP(v4) address as input:

        Does an exhaustive set of queries to find the associated
        network resources (short of recursing into TLDs).

        Checks the IP(v4) addresses found against Blacklist
        nameservers.

        If found to be a blacklisted IP(v4) address,
        reports the blacklist text records.
        (Usually hyper-links to the specific report.)

    Requires
        A working Internet connection.
        (Exercise: Add check and/or abort if not on-line when running script.)
        Bash with arrays (2.05b+).

        The external program 'dig' --
        a utility program provided with the 'bind' set of programs.
        Specifically, the version which is part of Bind series 9.x
        See: http://www.isc.org

        All usages of 'dig' are limited to wrapper functions,
        which may be rewritten as required.
        See: dig_wrappers.bash for details.
             ("Additional documentation" -- below)

    Usage
        Script requires a single argument, which may be:
        1) A domain name;
        2) An IP(v4) address;
        3) A filename, with one name or address per line.

        Script accepts an optional second argument, which may be:
        1) A Blacklist server name;
        2) A filename, with one Blacklist server name per line.

        If the second argument is not provided, the script uses
        a built-in set of (free) Blacklist servers.

        See also, the Quickstart at the end of this script (after 'exit').

    Return Codes
        0 - All OK
        1 - Script failure
        2 - Something is Blacklisted

    Optional environment variables
        SPAMMER_TRACE
            If set to a writable file,
            script will log an execution flow trace.

        SPAMMER_DATA
            If set to a writable file, script will dump its
            discovered data in the form of GraphViz file.
            See: http://www.research.att.com/sw/tools/graphviz

        SPAMMER_LIMIT
            Limits the depth of resource tracing.

            Default is 2 levels.

            A setting of 0 (zero) means 'unlimited' . . .
              Caution: script might recurse the whole Internet!

            A limit of 1 or 2 is most useful when processing
            a file of domain names and addresses.
            A higher limit can be useful when hunting spam gangs.

    Additional documentation
        Download the archived set of scripts
        explaining and illustrating the function contained within this script.
        http://bash.deta.in/mszick_clf.tar.bz2

    Study notes
        This script uses a large number of functions.
        Nearly all general functions have their own example script.
        Each of the example scripts have tutorial level comments.

    Scripting project
        Add support for IP(v6) addresses.
        IP(v6) addresses are recognized but not processed.

    Advanced project
        Add the reverse lookup detail to the discovered information.

        Report the delegation chain and abuse contacts.

        Modify the GraphViz file output to include the
        newly discovered information.

    __is_spammer_Doc_

    #######################################################

    #### Special IFS settings used for string parsing. ####

    # Whitespace == :Space:Tab:Line Feed:Carriage Return:
    WSP_IFS=$'\x20'$'\x09'$'\x0A'$'\x0D'

    # No Whitespace == Line Feed:Carriage Return
    NO_WSP=$'\x0A'$'\x0D'

    # Field separator for dotted decimal IP addresses
    ADR_IFS=${NO_WSP}'.'

    # Array to dotted string conversions
    DOT_IFS='.'${WSP_IFS}

    # # # Pending operations stack machine # # #
    # This set of functions described in func_stack.bash.
    # (See "Additional documentation" above.)
    # # #

    # Global stack of pending operations.
    declare -f -a _pending_
    # Global sentinel for stack runners
    declare -i _p_ctrl_
    # Global holder for currently executing function
    declare -f _pend_current_

    # # # Debug version only - remove for regular use # # #
    #
    # The function stored in _pend_hook_ is called
    # immediately before each pending function is
    # evaluated.  Stack clean, _pend_current_ set.
    #
    # This thingy demonstrated in pend_hook.bash.
    declare -f _pend_hook_
    # # #

    # The do nothing function
    pend_dummy() { : ; }

    # Clear and initialize the function stack.
    pend_init() {
        unset _pending_[@]
        pend_func pend_stop_mark
        _pend_hook_='pend_dummy'  # Debug only.
    }

    # Discard the top function on the stack.
    pend_pop() {
        if [ ${#_pending_[@]} -gt 0 ]
        then
            local -i _top_
            _top_=${#_pending_[@]}-1
            unset _pending_[$_top_]
        fi
    }

    # pend_func function_name [$(printf '%q\n' arguments)]
    pend_func() {
        local IFS=${NO_WSP}
        set -f
        _pending_[${#_pending_[@]}]=$@
        set +f
    }

    # The function which stops the release:
    pend_stop_mark() {
        _p_ctrl_=0
    }

    pend_mark() {
        pend_func pend_stop_mark
    }

    # Execute functions until 'pend_stop_mark' . . .
    pend_release() {
        local -i _top_             # Declare _top_ as integer.
        _p_ctrl_=${#_pending_[@]}
        while [ ${_p_ctrl_} -gt 0 ]
        do
           _top_=${#_pending_[@]}-1
           _pend_current_=${_pending_[$_top_]}
           unset _pending_[$_top_]
           $_pend_hook_            # Debug only.
           eval $_pend_current_
        done
    }

    # Drop functions until 'pend_stop_mark' . . .
    pend_drop() {
        local -i _top_
        local _pd_ctrl_=${#_pending_[@]}
        while [ ${_pd_ctrl_} -gt 0 ]
        do
           _top_=$_pd_ctrl_-1
           if [ "${_pending_[$_top_]}" == 'pend_stop_mark' ]
           then
               unset _pending_[$_top_]
               break
           else
               unset _pending_[$_top_]
               _pd_ctrl_=$_top_
           fi
        done
        if [ ${#_pending_[@]} -eq 0 ]
        then
            pend_func pend_stop_mark
        fi
    }

    #### Array editors ####

    # This function described in edit_exact.bash.
    # (See "Additional documentation," above.)
    # edit_exact <excludes_array_name> <target_array_name>
    edit_exact() {
        [ $# -eq 2 ] ||
        [ $# -eq 3 ] || return 1
        local -a _ee_Excludes
        local -a _ee_Target
        local _ee_x
        local _ee_t
        local IFS=${NO_WSP}
        set -f
        eval _ee_Excludes=\( \$\{$1\[@\]\} \)
        eval _ee_Target=\( \$\{$2\[@\]\} \)
        local _ee_len=${#_ee_Target[@]}     # Original length.
        local _ee_cnt=${#_ee_Excludes[@]}   # Exclude list length.
        [ ${_ee_len} -ne 0 ] || return 0    # Can't edit zero length.
        [ ${_ee_cnt} -ne 0 ] || return 0    # Can't edit zero length.
        for (( x = 0; x < ${_ee_cnt} ; x++ ))
        do
            _ee_x=${_ee_Excludes[$x]}
            for (( n = 0 ; n < ${_ee_len} ; n++ ))
            do
                _ee_t=${_ee_Target[$n]}
                if [ x"${_ee_t}" == x"${_ee_x}" ]
                then
                    unset _ee_Target[$n]     # Discard match.
                    [ $# -eq 2 ] && break    # If 2 arguments, then done.
                fi
            done
        done
        eval $2=\( \$\{_ee_Target\[@\]\} \)
        set +f
        return 0
    }

    # This function described in edit_by_glob.bash.
    # edit_by_glob <excludes_array_name> <target_array_name>
    edit_by_glob() {
        [ $# -eq 2 ] ||
        [ $# -eq 3 ] || return 1
        local -a _ebg_Excludes
        local -a _ebg_Target
        local _ebg_x
        local _ebg_t
        local IFS=${NO_WSP}
        set -f
        eval _ebg_Excludes=\( \$\{$1\[@\]\} \)
        eval _ebg_Target=\( \$\{$2\[@\]\} \)
        local _ebg_len=${#_ebg_Target[@]}
        local _ebg_cnt=${#_ebg_Excludes[@]}
        [ ${_ebg_len} -ne 0 ] || return 0
        [ ${_ebg_cnt} -ne 0 ] || return 0
        for (( x = 0; x < ${_ebg_cnt} ; x++ ))
        do
            _ebg_x=${_ebg_Excludes[$x]}
            for (( n = 0 ; n < ${_ebg_len} ; n++ ))
            do
                [ $# -eq 3 ] && _ebg_x=${_ebg_x}'*'  #  Do prefix edit
                if [ ${_ebg_Target[$n]:=} ]          #+ if defined & set.
                then
                    _ebg_t=${_ebg_Target[$n]/#${_ebg_x}/}
                    [ ${#_ebg_t} -eq 0 ] && unset _ebg_Target[$n]
                fi
            done
        done
        eval $2=\( \$\{_ebg_Target\[@\]\} \)
        set +f
        return 0
    }

    # This function described in unique_lines.bash.
    # unique_lines <in_name> <out_name>
    unique_lines() {
        [ $# -eq 2 ] || return 1
        local -a _ul_in
        local -a _ul_out
        local -i _ul_cnt
        local -i _ul_pos
        local _ul_tmp
        local IFS=${NO_WSP}
        set -f
        eval _ul_in=\( \$\{$1\[@\]\} \)
        _ul_cnt=${#_ul_in[@]}
        for (( _ul_pos = 0 ; _ul_pos < ${_ul_cnt} ; _ul_pos++ ))
        do
            if [ ${_ul_in[${_ul_pos}]:=} ]      # If defined & not empty
            then
                _ul_tmp=${_ul_in[${_ul_pos}]}
                _ul_out[${#_ul_out[@]}]=${_ul_tmp}
                for (( zap = _ul_pos ; zap < ${_ul_cnt} ; zap++ ))
                do
                    [ ${_ul_in[${zap}]:=} ] &&
                    [ 'x'${_ul_in[${zap}]} == 'x'${_ul_tmp} ] &&
                        unset _ul_in[${zap}]
                done
            fi
        done
        eval $2=\( \$\{_ul_out\[@\]\} \)
        set +f
        return 0
    }

    # This function described in char_convert.bash.
    # to_lower <string>
    to_lower() {
        [ $# -eq 1 ] || return 1
        local _tl_out
        _tl_out=${1//A/a}
        _tl_out=${_tl_out//B/b}
        _tl_out=${_tl_out//C/c}
        _tl_out=${_tl_out//D/d}
        _tl_out=${_tl_out//E/e}
        _tl_out=${_tl_out//F/f}
        _tl_out=${_tl_out//G/g}
        _tl_out=${_tl_out//H/h}
        _tl_out=${_tl_out//I/i}
        _tl_out=${_tl_out//J/j}
        _tl_out=${_tl_out//K/k}
        _tl_out=${_tl_out//L/l}
        _tl_out=${_tl_out//M/m}
        _tl_out=${_tl_out//N/n}
        _tl_out=${_tl_out//O/o}
        _tl_out=${_tl_out//P/p}
        _tl_out=${_tl_out//Q/q}
        _tl_out=${_tl_out//R/r}
        _tl_out=${_tl_out//S/s}
        _tl_out=${_tl_out//T/t}
        _tl_out=${_tl_out//U/u}
        _tl_out=${_tl_out//V/v}
        _tl_out=${_tl_out//W/w}
        _tl_out=${_tl_out//X/x}
        _tl_out=${_tl_out//Y/y}
        _tl_out=${_tl_out//Z/z}
        echo ${_tl_out}
        return 0
    }

    #### Application helper functions ####

    # Not everybody uses dots as separators (APNIC, for example).
    # This function described in to_dot.bash
    # to_dot <string>
    to_dot() {
        [ $# -eq 1 ] || return 1
        echo ${1//[#|@|%]/.}
        return 0
    }

    # This function described in is_number.bash.
    # is_number <input>
    is_number() {
        [ "$#" -eq 1 ]    || return 1  # is blank?
        [ x"$1" == 'x0' ] && return 0  # is zero?
        local -i tst
        let tst=$1 2>/dev/null         # else is numeric!
        return $?
    }

    # This function described in is_address.bash.
    # is_address <input>
    is_address() {
        [ $# -eq 1 ] || return 1    # Blank ==> false
        local -a _ia_input
        local IFS=${ADR_IFS}
        _ia_input=( $1 )
        if  [ ${#_ia_input[@]} -eq 4 ]  &&
            is_number ${_ia_input[0]}   &&
            is_number ${_ia_input[1]}   &&
            is_number ${_ia_input[2]}   &&
            is_number ${_ia_input[3]}   &&
            [ ${_ia_input[0]} -lt 256 ] &&
            [ ${_ia_input[1]} -lt 256 ] &&
            [ ${_ia_input[2]} -lt 256 ] &&
            [ ${_ia_input[3]} -lt 256 ]
        then
            return 0
        else
            return 1
        fi
    }

    #  This function described in split_ip.bash.
    #  split_ip <IP_address>
    #+ <array_name_norm> [<array_name_rev>]
    split_ip() {
        [ $# -eq 3 ] ||              #  Either three
        [ $# -eq 2 ] || return 1     #+ or two arguments
        local -a _si_input
        local IFS=${ADR_IFS}
        _si_input=( $1 )
        IFS=${WSP_IFS}
        eval $2=\(\ \$\{_si_input\[@\]\}\ \)
        if [ $# -eq 3 ]
        then
            # Build query order array.
            local -a _dns_ip
            _dns_ip[0]=${_si_input[3]}
            _dns_ip[1]=${_si_input[2]}
            _dns_ip[2]=${_si_input[1]}
            _dns_ip[3]=${_si_input[0]}
            eval $3=\(\ \$\{_dns_ip\[@\]\}\ \)
        fi
        return 0
    }

    # This function described in dot_array.bash.
    # dot_array <array_name>
    dot_array() {
        [ $# -eq 1 ] || return 1     # Single argument required.
        local -a _da_input
        eval _da_input=\(\ \$\{$1\[@\]\}\ \)
        local IFS=${DOT_IFS}
        local _da_output=${_da_input[@]}
        IFS=${WSP_IFS}
        echo ${_da_output}
        return 0
    }

    # This function described in file_to_array.bash
    # file_to_array <file_name> <line_array_name>
    file_to_array() {
        [ $# -eq 2 ] || return 1  # Two arguments required.
        local IFS=${NO_WSP}
        local -a _fta_tmp_
        _fta_tmp_=( $(cat $1) )
        eval $2=\( \$\{_fta_tmp_\[@\]\} \)
        return 0
    }

    #  Columnized print of an array of multi-field strings.
    #  col_print <array_name> <min_space> <
    #+ tab_stop [tab_stops]>
    col_print() {
        [ $# -gt 2 ] || return 0
        local -a _cp_inp
        local -a _cp_spc
        local -a _cp_line
        local _cp_min
        local _cp_mcnt
        local _cp_pos
        local _cp_cnt
        local _cp_tab
        local -i _cp
        local -i _cpf
        local _cp_fld
        # WARNING: FOLLOWING LINE NOT BLANK -- IT IS QUOTED SPACES.
        local _cp_max='                                                            '
        set -f
        local IFS=${NO_WSP}
        eval _cp_inp=\(\ \$\{$1\[@\]\}\ \)
        [ ${#_cp_inp[@]} -gt 0 ] || return 0 # Empty is easy.
        _cp_mcnt=$2
        _cp_min=${_cp_max:1:${_cp_mcnt}}
        shift
        shift
        _cp_cnt=$#
        for (( _cp = 0 ; _cp < _cp_cnt ; _cp++ ))
        do
            _cp_spc[${#_cp_spc[@]}]="${_cp_max:2:$1}" #"
            shift
        done
        _cp_cnt=${#_cp_inp[@]}
        for (( _cp = 0 ; _cp < _cp_cnt ; _cp++ ))
        do
            _cp_pos=1
            IFS=${NO_WSP}$'\x20'
            _cp_line=( ${_cp_inp[${_cp}]} )
            IFS=${NO_WSP}
            for (( _cpf = 0 ; _cpf < ${#_cp_line[@]} ; _cpf++ ))
            do
                _cp_tab=${_cp_spc[${_cpf}]:${_cp_pos}}
                if [ ${#_cp_tab} -lt ${_cp_mcnt} ]
                then
                    _cp_tab="${_cp_min}"
                fi
                echo -n "${_cp_tab}"
                (( _cp_pos = ${_cp_pos} + ${#_cp_tab} ))
                _cp_fld="${_cp_line[${_cpf}]}"
                echo -n ${_cp_fld}
                (( _cp_pos = ${_cp_pos} + ${#_cp_fld} ))
            done
            echo
        done
        set +f
        return 0
    }

    # # # # 'Hunt the Spammer' data flow # # # #

    # Application return code
    declare -i _hs_RC

    # Original input, from which IP addresses are removed
    # After which, domain names to check
    declare -a uc_name

    # Original input IP addresses are moved here
    # After which, IP addresses to check
    declare -a uc_address

    # Names against which address expansion run
    # Ready for name detail lookup
    declare -a chk_name

    # Addresses against which name expansion run
    # Ready for address detail lookup
    declare -a chk_address

    #  Recursion is depth-first-by-name.
    #  The expand_input_address maintains this list
    #+ to prohibit looking up addresses twice during
    #+ domain name recursion.
    declare -a been_there_addr
    been_there_addr=( '127.0.0.1' ) # Whitelist localhost

    # Names which we have checked (or given up on)
    declare -a known_name

    # Addresses which we have checked (or given up on)
    declare -a known_address

    #  List of zero or more Blacklist servers to check.
    #  Each 'known_address' will be checked against each server,
    #+ with negative replies and failures suppressed.
    declare -a list_server

    # Indirection limit - set to zero == no limit
    indirect=${SPAMMER_LIMIT:=2}

    # # # # 'Hunt the Spammer' information output data # # # #

    # Any domain name may have multiple IP addresses.
    # Any IP address may have multiple domain names.
    # Therefore, track unique address-name pairs.
    declare -a known_pair
    declare -a reverse_pair

    #  In addition to the data flow variables; known_address
    #+ known_name and list_server, the following are output to the
    #+ external graphics interface file.

    # Authority chain, parent -> SOA fields.
    declare -a auth_chain

    # Reference chain, parent name -> child name
    declare -a ref_chain

    # DNS chain - domain name -> address
    declare -a name_address

    # Name and service pairs - domain name -> service
    declare -a name_srvc

    # Name and resource pairs - domain name -> Resource Record
    declare -a name_resource

    # Parent and Child pairs - parent name -> child name
    # This MAY NOT be the same as the ref_chain followed!
    declare -a parent_child

    # Address and Blacklist hit pairs - address->server
    declare -a address_hits

    # Dump interface file data
    declare -f _dot_dump
    _dot_dump=pend_dummy   # Initially a no-op

    #  Data dump is enabled by setting the environment variable SPAMMER_DATA
    #+ to the name of a writable file.
    declare _dot_file

    # Helper function for the dump-to-dot-file function
    # dump_to_dot <array_name> <prefix>
    dump_to_dot() {
        local -a _dda_tmp
        local -i _dda_cnt
        local _dda_form='    '${2}'%04u %s\n'
        local IFS=${NO_WSP}
        eval _dda_tmp=\(\ \$\{$1\[@\]\}\ \)
        _dda_cnt=${#_dda_tmp[@]}
        if [ ${_dda_cnt} -gt 0 ]
        then
            for (( _dda = 0 ; _dda < _dda_cnt ; _dda++ ))
            do
                printf "${_dda_form}" \
                       "${_dda}" "${_dda_tmp[${_dda}]}" >>${_dot_file}
            done
        fi
    }

    # Which will also set _dot_dump to this function . . .
    dump_dot() {
        local -i _dd_cnt
        echo '# Data vintage: '$(date -R) >${_dot_file}
        echo '# ABS Guide: is_spammer.bash; v2, 2004-msz' >>${_dot_file}
        echo >>${_dot_file}
        echo 'digraph G {' >>${_dot_file}

        if [ ${#known_name[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known domain name nodes' >>${_dot_file}
            _dd_cnt=${#known_name[@]}
            for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
            do
                printf '    N%04u [label="%s"] ;\n' \
                       "${_dd}" "${known_name[${_dd}]}" >>${_dot_file}
            done
        fi

        if [ ${#known_address[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known address nodes' >>${_dot_file}
            _dd_cnt=${#known_address[@]}
            for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
            do
                printf '    A%04u [label="%s"] ;\n' \
                       "${_dd}" "${known_address[${_dd}]}" >>${_dot_file}
            done
        fi

        echo                                   >>${_dot_file}
        echo '/*'                              >>${_dot_file}
        echo ' * Known relationships :: User conversion to'  >>${_dot_file}
        echo ' * graphic form by hand or program required.'  >>${_dot_file}
        echo ' *'                              >>${_dot_file}

        if [ ${#auth_chain[@]} -gt 0 ]
        then
          echo >>${_dot_file}
          echo '# Authority ref. edges followed & field source.' >>${_dot_file}
            dump_to_dot auth_chain AC
        fi

        if [ ${#ref_chain[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Name ref. edges followed and field source.' >>${_dot_file}
            dump_to_dot ref_chain RC
        fi

        if [ ${#name_address[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known name->address edges' >>${_dot_file}
            dump_to_dot name_address NA
        fi

        if [ ${#name_srvc[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known name->service edges' >>${_dot_file}
            dump_to_dot name_srvc NS
        fi

        if [ ${#name_resource[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known name->resource edges' >>${_dot_file}
            dump_to_dot name_resource NR
        fi

        if [ ${#parent_child[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known parent->child edges' >>${_dot_file}
            dump_to_dot parent_child PC
        fi

        if [ ${#list_server[@]} -gt 0 ]
        then
            echo >>${_dot_file}
            echo '# Known Blacklist nodes' >>${_dot_file}
            _dd_cnt=${#list_server[@]}
            for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
            do
                printf '    LS%04u [label="%s"] ;\n' \
                       "${_dd}" "${list_server[${_dd}]}" >>${_dot_file}
            done
        fi

        unique_lines address_hits address_hits
        if [ ${#address_hits[@]} -gt 0 ]
        then
          echo >>${_dot_file}
          echo '# Known address->Blacklist_hit edges' >>${_dot_file}
          echo '# CAUTION: dig warnings can trigger false hits.' >>${_dot_file}
           dump_to_dot address_hits AH
        fi
        echo          >>${_dot_file}
        echo ' *'     >>${_dot_file}
        echo ' * That is a lot of relationships. Happy graphing.' >>${_dot_file}
        echo ' */'    >>${_dot_file}
        echo '}'      >>${_dot_file}
        return 0
    }

    # # # # 'Hunt the Spammer' execution flow # # # #

    #  Execution trace is enabled by setting the
    #+ environment variable SPAMMER_TRACE to the name of a writable file.
    declare -a _trace_log
    declare _log_file

    # Function to fill the trace log
    trace_logger() {
        _trace_log[${#_trace_log[@]}]=${_pend_current_}
    }

    # Dump trace log to file function variable.
    declare -f _log_dump
    _log_dump=pend_dummy   # Initially a no-op.

    # Dump the trace log to a file.
    dump_log() {
        local -i _dl_cnt
        _dl_cnt=${#_trace_log[@]}
        for (( _dl = 0 ; _dl < _dl_cnt ; _dl++ ))
        do
            echo ${_trace_log[${_dl}]} >> ${_log_file}
        done
        _dl_cnt=${#_pending_[@]}
        if [ ${_dl_cnt} -gt 0 ]
        then
            _dl_cnt=${_dl_cnt}-1
            echo '# # # Operations stack not empty # # #' >> ${_log_file}
            for (( _dl = ${_dl_cnt} ; _dl >= 0 ; _dl-- ))
            do
                echo ${_pending_[${_dl}]} >> ${_log_file}
            done
        fi
    }

    # # # Utility program 'dig' wrappers # # #
    #
    #  These wrappers are derived from the
    #+ examples shown in dig_wrappers.bash.
    #
    #  The major difference is these return
    #+ their results as a list in an array.
    #
    #  See dig_wrappers.bash for details and
    #+ use that script to develop any changes.
    #
    # # #

    # Short form answer: 'dig' parses answer.

    # Forward lookup :: Name -> Address
    # short_fwd <domain_name> <array_name>
    short_fwd() {
        local -a _sf_reply
        local -i _sf_rc
        local -i _sf_cnt
        IFS=${NO_WSP}
    echo -n '.'
    # echo 'sfwd: '${1}
      _sf_reply=( $(dig +short ${1} -c in -t a 2>/dev/null) )
      _sf_rc=$?
      if [ ${_sf_rc} -ne 0 ]
      then
        _trace_log[${#_trace_log[@]}]='## Lookup error '${_sf_rc}' on '${1}' ##'
    # [ ${_sf_rc} -ne 9 ] && pend_drop
            return ${_sf_rc}
        else
            # Some versions of 'dig' return warnings on stdout.
            _sf_cnt=${#_sf_reply[@]}
            for (( _sf = 0 ; _sf < ${_sf_cnt} ; _sf++ ))
            do
                [ 'x'${_sf_reply[${_sf}]:0:2} == 'x;;' ] &&
                    unset _sf_reply[${_sf}]
            done
            eval $2=\( \$\{_sf_reply\[@\]\} \)
        fi
        return 0
    }

    # Reverse lookup :: Address -> Name
    # short_rev <ip_address> <array_name>
    short_rev() {
        local -a _sr_reply
        local -i _sr_rc
        local -i _sr_cnt
        IFS=${NO_WSP}
    echo -n '.'
    # echo 'srev: '${1}
      _sr_reply=( $(dig +short -x ${1} 2>/dev/null) )
      _sr_rc=$?
      if [ ${_sr_rc} -ne 0 ]
      then
        _trace_log[${#_trace_log[@]}]='## Lookup error '${_sr_rc}' on '${1}' ##'
    # [ ${_sr_rc} -ne 9 ] && pend_drop
            return ${_sr_rc}
        else
            # Some versions of 'dig' return warnings on stdout.
            _sr_cnt=${#_sr_reply[@]}
            for (( _sr = 0 ; _sr < ${_sr_cnt} ; _sr++ ))
            do
                [ 'x'${_sr_reply[${_sr}]:0:2} == 'x;;' ] &&
                    unset _sr_reply[${_sr}]
            done
            eval $2=\( \$\{_sr_reply\[@\]\} \)
        fi
        return 0
    }

    # Special format lookup used to query blacklist servers.
    # short_text <ip_address> <array_name>
    short_text() {
        local -a _st_reply
        local -i _st_rc
        local -i _st_cnt
        IFS=${NO_WSP}
    # echo 'stxt: '${1}
      _st_reply=( $(dig +short ${1} -c in -t txt 2>/dev/null) )
      _st_rc=$?
      if [ ${_st_rc} -ne 0 ]
      then
        _trace_log[${#_trace_log[@]}]='##Text lookup error '${_st_rc}' on '${1}'##'
    # [ ${_st_rc} -ne 9 ] && pend_drop
            return ${_st_rc}
        else
            # Some versions of 'dig' return warnings on stdout.
            _st_cnt=${#_st_reply[@]}
            for (( _st = 0 ; _st < ${#_st_cnt} ; _st++ ))
            do
                [ 'x'${_st_reply[${_st}]:0:2} == 'x;;' ] &&
                    unset _st_reply[${_st}]
            done
            eval $2=\( \$\{_st_reply\[@\]\} \)
        fi
        return 0
    }

    # The long forms, a.k.a., the parse it yourself versions

    # RFC 2782   Service lookups
    # dig +noall +nofail +answer _ldap._tcp.openldap.org -t srv
    # _<service>._<protocol>.<domain_name>
    # _ldap._tcp.openldap.org. 3600   IN     SRV    0 0 389 ldap.openldap.org.
    # domain TTL Class SRV Priority Weight Port Target

    # Forward lookup :: Name -> poor man's zone transfer
    # long_fwd <domain_name> <array_name>
    long_fwd() {
        local -a _lf_reply
        local -i _lf_rc
        local -i _lf_cnt
        IFS=${NO_WSP}
    echo -n ':'
    # echo 'lfwd: '${1}
      _lf_reply=( $(
         dig +noall +nofail +answer +authority +additional \
             ${1} -t soa ${1} -t mx ${1} -t any 2>/dev/null) )
      _lf_rc=$?
      if [ ${_lf_rc} -ne 0 ]
      then
        _trace_log[${#_trace_log[@]}]='# Zone lookup err '${_lf_rc}' on '${1}' #'
    # [ ${_lf_rc} -ne 9 ] && pend_drop
            return ${_lf_rc}
        else
            # Some versions of 'dig' return warnings on stdout.
            _lf_cnt=${#_lf_reply[@]}
            for (( _lf = 0 ; _lf < ${_lf_cnt} ; _lf++ ))
            do
                [ 'x'${_lf_reply[${_lf}]:0:2} == 'x;;' ] &&
                    unset _lf_reply[${_lf}]
            done
            eval $2=\( \$\{_lf_reply\[@\]\} \)
        fi
        return 0
    }
    #  The reverse lookup domain name corresponding to the IPv6 address:
    #      4321:0:1:2:3:4:567:89ab
    #  would be (nibble, I.E: Hexdigit) reversed:
    #  b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.ARPA.

    # Reverse lookup :: Address -> poor man's delegation chain
    # long_rev <rev_ip_address> <array_name>
    long_rev() {
        local -a _lr_reply
        local -i _lr_rc
        local -i _lr_cnt
        local _lr_dns
        _lr_dns=${1}'.in-addr.arpa.'
        IFS=${NO_WSP}
    echo -n ':'
    # echo 'lrev: '${1}
      _lr_reply=( $(
           dig +noall +nofail +answer +authority +additional \
               ${_lr_dns} -t soa ${_lr_dns} -t any 2>/dev/null) )
      _lr_rc=$?
      if [ ${_lr_rc} -ne 0 ]
      then
        _trace_log[${#_trace_log[@]}]='# Deleg lkp error '${_lr_rc}' on '${1}' #'
    # [ ${_lr_rc} -ne 9 ] && pend_drop
            return ${_lr_rc}
        else
            # Some versions of 'dig' return warnings on stdout.
            _lr_cnt=${#_lr_reply[@]}
            for (( _lr = 0 ; _lr < ${_lr_cnt} ; _lr++ ))
            do
                [ 'x'${_lr_reply[${_lr}]:0:2} == 'x;;' ] &&
                    unset _lr_reply[${_lr}]
            done
            eval $2=\( \$\{_lr_reply\[@\]\} \)
        fi
        return 0
    }

    # # # Application specific functions # # #

    # Mung a possible name; suppresses root and TLDs.
    # name_fixup <string>
    name_fixup(){
        local -a _nf_tmp
        local -i _nf_end
        local _nf_str
        local IFS
        _nf_str=$(to_lower ${1})
        _nf_str=$(to_dot ${_nf_str})
        _nf_end=${#_nf_str}-1
        [ ${_nf_str:${_nf_end}} != '.' ] &&
            _nf_str=${_nf_str}'.'
        IFS=${ADR_IFS}
        _nf_tmp=( ${_nf_str} )
        IFS=${WSP_IFS}
        _nf_end=${#_nf_tmp[@]}
        case ${_nf_end} in
        0) # No dots, only dots.
            echo
            return 1
        ;;
        1) # Only a TLD.
            echo
            return 1
        ;;
        2) # Maybe okay.
           echo ${_nf_str}
           return 0
           # Needs a lookup table?
           if [ ${#_nf_tmp[1]} -eq 2 ]
           then # Country coded TLD.
               echo
               return 1
           else
               echo ${_nf_str}
               return 0
           fi
        ;;
        esac
        echo ${_nf_str}
        return 0
    }

    # Grope and mung original input(s).
    split_input() {
        [ ${#uc_name[@]} -gt 0 ] || return 0
        local -i _si_cnt
        local -i _si_len
        local _si_str
        unique_lines uc_name uc_name
        _si_cnt=${#uc_name[@]}
        for (( _si = 0 ; _si < _si_cnt ; _si++ ))
        do
            _si_str=${uc_name[$_si]}
            if is_address ${_si_str}
            then
                uc_address[${#uc_address[@]}]=${_si_str}
                unset uc_name[$_si]
            else
                if ! uc_name[$_si]=$(name_fixup ${_si_str})
                then
                    unset ucname[$_si]
                fi
            fi
        done
      uc_name=( ${uc_name[@]} )
      _si_cnt=${#uc_name[@]}
      _trace_log[${#_trace_log[@]}]='#Input '${_si_cnt}' unchkd name input(s).#'
      _si_cnt=${#uc_address[@]}
      _trace_log[${#_trace_log[@]}]='#Input '${_si_cnt}' unchkd addr input(s).#'
        return 0
    }

    # # # Discovery functions -- recursively interlocked by external data # # #
    # # # The leading 'if list is empty; return 0' in each is required. # # #

    # Recursion limiter
    # limit_chk() <next_level>
    limit_chk() {
        local -i _lc_lmt
        # Check indirection limit.
        if [ ${indirect} -eq 0 ] || [ $# -eq 0 ]
        then
            # The 'do-forever' choice
            echo 1                 # Any value will do.
            return 0               # OK to continue.
        else
            # Limiting is in effect.
            if [ ${indirect} -lt ${1} ]
            then
                echo ${1}          # Whatever.
                return 1           # Stop here.
            else
                _lc_lmt=${1}+1     # Bump the given limit.
                echo ${_lc_lmt}    # Echo it.
                return 0           # OK to continue.
            fi
        fi
    }

    # For each name in uc_name:
    #     Move name to chk_name.
    #     Add addresses to uc_address.
    #     Pend expand_input_address.
    #     Repeat until nothing new found.
    # expand_input_name <indirection_limit>
    expand_input_name() {
        [ ${#uc_name[@]} -gt 0 ] || return 0
        local -a _ein_addr
        local -a _ein_new
        local -i _ucn_cnt
        local -i _ein_cnt
        local _ein_tst
        _ucn_cnt=${#uc_name[@]}

        if  ! _ein_cnt=$(limit_chk ${1})
        then
            return 0
        fi

        for (( _ein = 0 ; _ein < _ucn_cnt ; _ein++ ))
        do
            if short_fwd ${uc_name[${_ein}]} _ein_new
            then
              for (( _ein_cnt = 0 ; _ein_cnt < ${#_ein_new[@]}; _ein_cnt++ ))
              do
                  _ein_tst=${_ein_new[${_ein_cnt}]}
                  if is_address ${_ein_tst}
                  then
                      _ein_addr[${#_ein_addr[@]}]=${_ein_tst}
                  fi
        done
            fi
        done
        unique_lines _ein_addr _ein_addr     # Scrub duplicates.
        edit_exact chk_address _ein_addr     # Scrub pending detail.
        edit_exact known_address _ein_addr   # Scrub already detailed.
     if [ ${#_ein_addr[@]} -gt 0 ]        # Anything new?
     then
       uc_address=( ${uc_address[@]} ${_ein_addr[@]} )
       pend_func expand_input_address ${1}
       _trace_log[${#_trace_log[@]}]='#Add '${#_ein_addr[@]}' unchkd addr inp.#'
        fi
        edit_exact chk_name uc_name          # Scrub pending detail.
        edit_exact known_name uc_name        # Scrub already detailed.
        if [ ${#uc_name[@]} -gt 0 ]
        then
            chk_name=( ${chk_name[@]} ${uc_name[@]}  )
            pend_func detail_each_name ${1}
        fi
        unset uc_name[@]
        return 0
    }

    # For each address in uc_address:
    #     Move address to chk_address.
    #     Add names to uc_name.
    #     Pend expand_input_name.
    #     Repeat until nothing new found.
    # expand_input_address <indirection_limit>
    expand_input_address() {
        [ ${#uc_address[@]} -gt 0 ] || return 0
        local -a _eia_addr
        local -a _eia_name
        local -a _eia_new
        local -i _uca_cnt
        local -i _eia_cnt
        local _eia_tst
        unique_lines uc_address _eia_addr
        unset uc_address[@]
        edit_exact been_there_addr _eia_addr
        _uca_cnt=${#_eia_addr[@]}
        [ ${_uca_cnt} -gt 0 ] &&
            been_there_addr=( ${been_there_addr[@]} ${_eia_addr[@]} )

        for (( _eia = 0 ; _eia < _uca_cnt ; _eia++ ))
         do
           if short_rev ${_eia_addr[${_eia}]} _eia_new
           then
             for (( _eia_cnt = 0 ; _eia_cnt < ${#_eia_new[@]} ; _eia_cnt++ ))
             do
               _eia_tst=${_eia_new[${_eia_cnt}]}
               if _eia_tst=$(name_fixup ${_eia_tst})
               then
                 _eia_name[${#_eia_name[@]}]=${_eia_tst}
           fi
         done
               fi
        done
        unique_lines _eia_name _eia_name     # Scrub duplicates.
        edit_exact chk_name _eia_name        # Scrub pending detail.
        edit_exact known_name _eia_name      # Scrub already detailed.
     if [ ${#_eia_name[@]} -gt 0 ]        # Anything new?
     then
       uc_name=( ${uc_name[@]} ${_eia_name[@]} )
       pend_func expand_input_name ${1}
       _trace_log[${#_trace_log[@]}]='#Add '${#_eia_name[@]}' unchkd name inp.#'
        fi
        edit_exact chk_address _eia_addr     # Scrub pending detail.
        edit_exact known_address _eia_addr   # Scrub already detailed.
        if [ ${#_eia_addr[@]} -gt 0 ]        # Anything new?
        then
            chk_address=( ${chk_address[@]} ${_eia_addr[@]} )
            pend_func detail_each_address ${1}
        fi
        return 0
    }

    # The parse-it-yourself zone reply.
    # The input is the chk_name list.
    # detail_each_name <indirection_limit>
    detail_each_name() {
        [ ${#chk_name[@]} -gt 0 ] || return 0
        local -a _den_chk       # Names to check
        local -a _den_name      # Names found here
        local -a _den_address   # Addresses found here
        local -a _den_pair      # Pairs found here
        local -a _den_rev       # Reverse pairs found here
        local -a _den_tmp       # Line being parsed
        local -a _den_auth      # SOA contact being parsed
        local -a _den_new       # The zone reply
        local -a _den_pc        # Parent-Child gets big fast
        local -a _den_ref       # So does reference chain
        local -a _den_nr        # Name-Resource can be big
        local -a _den_na        # Name-Address
        local -a _den_ns        # Name-Service
        local -a _den_achn      # Chain of Authority
        local -i _den_cnt       # Count of names to detail
        local -i _den_lmt       # Indirection limit
        local _den_who          # Named being processed
        local _den_rec          # Record type being processed
        local _den_cont         # Contact domain
        local _den_str          # Fixed up name string
        local _den_str2         # Fixed up reverse
        local IFS=${WSP_IFS}

        # Local, unique copy of names to check
        unique_lines chk_name _den_chk
        unset chk_name[@]       # Done with globals.

        # Less any names already known
        edit_exact known_name _den_chk
        _den_cnt=${#_den_chk[@]}

        # If anything left, add to known_name.
        [ ${_den_cnt} -gt 0 ] &&
            known_name=( ${known_name[@]} ${_den_chk[@]} )

        # for the list of (previously) unknown names . . .
        for (( _den = 0 ; _den < _den_cnt ; _den++ ))
        do
            _den_who=${_den_chk[${_den}]}
            if long_fwd ${_den_who} _den_new
            then
                unique_lines _den_new _den_new
                if [ ${#_den_new[@]} -eq 0 ]
                then
                    _den_pair[${#_den_pair[@]}]='0.0.0.0 '${_den_who}
                fi

                # Parse each line in the reply.
                for (( _line = 0 ; _line < ${#_den_new[@]} ; _line++ ))
                do
                    IFS=${NO_WSP}$'\x09'$'\x20'
                    _den_tmp=( ${_den_new[${_line}]} )
                    IFS=${WSP_IFS}
                  # If usable record and not a warning message . . .
                  if [ ${#_den_tmp[@]} -gt 4 ] && [ 'x'${_den_tmp[0]} != 'x;;' ]
                  then
                        _den_rec=${_den_tmp[3]}
                        _den_nr[${#_den_nr[@]}]=${_den_who}' '${_den_rec}
                        # Begin at RFC1033 (+++)
                        case ${_den_rec} in

    #<name> [<ttl>]  [<class>] SOA <origin> <person>
                        SOA) # Start Of Authority
        if _den_str=$(name_fixup ${_den_tmp[0]})
        then
          _den_name[${#_den_name[@]}]=${_den_str}
          _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_str}' SOA'
          # SOA origin -- domain name of master zone record
          if _den_str2=$(name_fixup ${_den_tmp[4]})
          then
            _den_name[${#_den_name[@]}]=${_den_str2}
            _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_str2}' SOA.O'
          fi
          # Responsible party e-mail address (possibly bogus).
          # Possibility of first.last@domain.name ignored.
          set -f
          if _den_str2=$(name_fixup ${_den_tmp[5]})
          then
            IFS=${ADR_IFS}
            _den_auth=( ${_den_str2} )
            IFS=${WSP_IFS}
            if [ ${#_den_auth[@]} -gt 2 ]
            then
              _den_cont=${_den_auth[1]}
              for (( _auth = 2 ; _auth < ${#_den_auth[@]} ; _auth++ ))
              do
                _den_cont=${_den_cont}'.'${_den_auth[${_auth}]}
              done
              _den_name[${#_den_name[@]}]=${_den_cont}'.'
              _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_cont}'. SOA.C'
                                    fi
            fi
            set +f
                            fi
                        ;;

          A) # IP(v4) Address Record
          if _den_str=$(name_fixup ${_den_tmp[0]})
          then
            _den_name[${#_den_name[@]}]=${_den_str}
            _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' '${_den_str}
            _den_na[${#_den_na[@]}]=${_den_str}' '${_den_tmp[4]}
            _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' A'
          else
            _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' unknown.domain'
            _den_na[${#_den_na[@]}]='unknown.domain '${_den_tmp[4]}
            _den_ref[${#_den_ref[@]}]=${_den_who}' unknown.domain A'
          fi
          _den_address[${#_den_address[@]}]=${_den_tmp[4]}
          _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_tmp[4]}
                 ;;

                 NS) # Name Server Record
                 # Domain name being serviced (may be other than current)
                   if _den_str=$(name_fixup ${_den_tmp[0]})
                     then
                       _den_name[${#_den_name[@]}]=${_den_str}
                       _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' NS'

                 # Domain name of service provider
                 if _den_str2=$(name_fixup ${_den_tmp[4]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str2}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str2}' NSH'
                   _den_ns[${#_den_ns[@]}]=${_den_str2}' NS'
                   _den_pc[${#_den_pc[@]}]=${_den_str}' '${_den_str2}
                  fi
                   fi
                        ;;

                 MX) # Mail Server Record
                     # Domain name being serviced (wildcards not handled here)
                 if _den_str=$(name_fixup ${_den_tmp[0]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' MX'
                 fi
                 # Domain name of service provider
                 if _den_str=$(name_fixup ${_den_tmp[5]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' MXH'
                   _den_ns[${#_den_ns[@]}]=${_den_str}' MX'
                   _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
                 fi
                        ;;

                 PTR) # Reverse address record
                      # Special name
                 if _den_str=$(name_fixup ${_den_tmp[0]})
                 then
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' PTR'
                   # Host name (not a CNAME)
                   if _den_str2=$(name_fixup ${_den_tmp[4]})
                   then
                     _den_rev[${#_den_rev[@]}]=${_den_str}' '${_den_str2}
                     _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str2}' PTRH'
                     _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
                   fi
                 fi
                        ;;

                 AAAA) # IP(v6) Address Record
                 if _den_str=$(name_fixup ${_den_tmp[0]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' '${_den_str}
                   _den_na[${#_den_na[@]}]=${_den_str}' '${_den_tmp[4]}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' AAAA'
                   else
                     _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' unknown.domain'
                     _den_na[${#_den_na[@]}]='unknown.domain '${_den_tmp[4]}
                     _den_ref[${#_den_ref[@]}]=${_den_who}' unknown.domain'
                   fi
                   # No processing for IPv6 addresses
                   _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_tmp[4]}
                        ;;

                 CNAME) # Alias name record
                        # Nickname
                 if _den_str=$(name_fixup ${_den_tmp[0]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' CNAME'
                   _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
                 fi
                        # Hostname
                 if _den_str=$(name_fixup ${_den_tmp[4]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' CHOST'
                   _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
                 fi
                        ;;
    #            TXT)
    #            ;;
                        esac
                    fi
                done
            else # Lookup error == 'A' record 'unknown address'
                _den_pair[${#_den_pair[@]}]='0.0.0.0 '${_den_who}
            fi
        done

        # Control dot array growth.
        unique_lines _den_achn _den_achn      # Works best, all the same.
        edit_exact auth_chain _den_achn       # Works best, unique items.
        if [ ${#_den_achn[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            auth_chain=( ${auth_chain[@]} ${_den_achn[@]} )
            IFS=${WSP_IFS}
        fi

        unique_lines _den_ref _den_ref      # Works best, all the same.
        edit_exact ref_chain _den_ref       # Works best, unique items.
        if [ ${#_den_ref[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            ref_chain=( ${ref_chain[@]} ${_den_ref[@]} )
            IFS=${WSP_IFS}
        fi

        unique_lines _den_na _den_na
        edit_exact name_address _den_na
        if [ ${#_den_na[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            name_address=( ${name_address[@]} ${_den_na[@]} )
            IFS=${WSP_IFS}
        fi

        unique_lines _den_ns _den_ns
        edit_exact name_srvc _den_ns
        if [ ${#_den_ns[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            name_srvc=( ${name_srvc[@]} ${_den_ns[@]} )
            IFS=${WSP_IFS}
        fi

        unique_lines _den_nr _den_nr
        edit_exact name_resource _den_nr
        if [ ${#_den_nr[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            name_resource=( ${name_resource[@]} ${_den_nr[@]} )
            IFS=${WSP_IFS}
        fi

        unique_lines _den_pc _den_pc
        edit_exact parent_child _den_pc
        if [ ${#_den_pc[@]} -gt 0 ]
        then
            IFS=${NO_WSP}
            parent_child=( ${parent_child[@]} ${_den_pc[@]} )
            IFS=${WSP_IFS}
        fi

        # Update list known_pair (Address and Name).
        unique_lines _den_pair _den_pair
        edit_exact known_pair _den_pair
        if [ ${#_den_pair[@]} -gt 0 ]  # Anything new?
        then
            IFS=${NO_WSP}
            known_pair=( ${known_pair[@]} ${_den_pair[@]} )
            IFS=${WSP_IFS}
        fi

        # Update list of reverse pairs.
        unique_lines _den_rev _den_rev
        edit_exact reverse_pair _den_rev
        if [ ${#_den_rev[@]} -gt 0 ]   # Anything new?
        then
            IFS=${NO_WSP}
            reverse_pair=( ${reverse_pair[@]} ${_den_rev[@]} )
            IFS=${WSP_IFS}
        fi

        # Check indirection limit -- give up if reached.
        if ! _den_lmt=$(limit_chk ${1})
        then
            return 0
        fi

    # Execution engine is LIFO. Order of pend operations is important.
    # Did we define any new addresses?
    unique_lines _den_address _den_address    # Scrub duplicates.
    edit_exact known_address _den_address     # Scrub already processed.
    edit_exact un_address _den_address        # Scrub already waiting.
    if [ ${#_den_address[@]} -gt 0 ]          # Anything new?
    then
      uc_address=( ${uc_address[@]} ${_den_address[@]} )
      pend_func expand_input_address ${_den_lmt}
      _trace_log[${#_trace_log[@]}]='# Add '${#_den_address[@]}' unchkd addr. #'
        fi

    # Did we find any new names?
    unique_lines _den_name _den_name          # Scrub duplicates.
    edit_exact known_name _den_name           # Scrub already processed.
    edit_exact uc_name _den_name              # Scrub already waiting.
    if [ ${#_den_name[@]} -gt 0 ]             # Anything new?
    then
      uc_name=( ${uc_name[@]} ${_den_name[@]} )
      pend_func expand_input_name ${_den_lmt}
      _trace_log[${#_trace_log[@]}]='#Added '${#_den_name[@]}' unchkd name#'
        fi
        return 0
    }

    # The parse-it-yourself delegation reply
    # Input is the chk_address list.
    # detail_each_address <indirection_limit>
    detail_each_address() {
        [ ${#chk_address[@]} -gt 0 ] || return 0
        unique_lines chk_address chk_address
        edit_exact known_address chk_address
        if [ ${#chk_address[@]} -gt 0 ]
        then
            known_address=( ${known_address[@]} ${chk_address[@]} )
            unset chk_address[@]
        fi
        return 0
    }

    # # # Application specific output functions # # #

    # Pretty print the known pairs.
    report_pairs() {
        echo
        echo 'Known network pairs.'
        col_print known_pair 2 5 30

        if [ ${#auth_chain[@]} -gt 0 ]
        then
            echo
            echo 'Known chain of authority.'
            col_print auth_chain 2 5 30 55
        fi

        if [ ${#reverse_pair[@]} -gt 0 ]
        then
            echo
            echo 'Known reverse pairs.'
            col_print reverse_pair 2 5 55
        fi
        return 0
    }

    # Check an address against the list of blacklist servers.
    # A good place to capture for GraphViz: address->status(server(reports))
    # check_lists <ip_address>
    check_lists() {
        [ $# -eq 1 ] || return 1
        local -a _cl_fwd_addr
        local -a _cl_rev_addr
        local -a _cl_reply
        local -i _cl_rc
        local -i _ls_cnt
        local _cl_dns_addr
        local _cl_lkup

        split_ip ${1} _cl_fwd_addr _cl_rev_addr
        _cl_dns_addr=$(dot_array _cl_rev_addr)'.'
        _ls_cnt=${#list_server[@]}
        echo '    Checking address '${1}
        for (( _cl = 0 ; _cl < _ls_cnt ; _cl++ ))
        do
          _cl_lkup=${_cl_dns_addr}${list_server[${_cl}]}
          if short_text ${_cl_lkup} _cl_reply
          then
            if [ ${#_cl_reply[@]} -gt 0 ]
            then
              echo '        Records from '${list_server[${_cl}]}
              address_hits[${#address_hits[@]}]=${1}' '${list_server[${_cl}]}
              _hs_RC=2
              for (( _clr = 0 ; _clr < ${#_cl_reply[@]} ; _clr++ ))
              do
                echo '            '${_cl_reply[${_clr}]}
              done
            fi
          fi
        done
        return 0
    }

    # # # The usual application glue # # #

    # Who did it?
    credits() {
       echo
       echo 'Advanced Bash Scripting Guide: is_spammer.bash, v2, 2004-msz'
    }

    # How to use it?
    # (See also, "Quickstart" at end of script.)
    usage() {
        cat <<-'_usage_statement_'
        The script is_spammer.bash requires either one or two arguments.

        arg 1) May be one of:
            a) A domain name
            b) An IPv4 address
            c) The name of a file with any mix of names
               and addresses, one per line.

        arg 2) May be one of:
            a) A Blacklist server domain name
            b) The name of a file with Blacklist server
               domain names, one per line.
            c) If not present, a default list of (free)
               Blacklist servers is used.
            d) If a filename of an empty, readable, file
               is given,
               Blacklist server lookup is disabled.

        All script output is written to stdout.

        Return codes: 0 -> All OK, 1 -> Script failure,
                      2 -> Something is Blacklisted.

        Requires the external program 'dig' from the 'bind-9'
        set of DNS programs.  See: http://www.isc.org

        The domain name lookup depth limit defaults to 2 levels.
        Set the environment variable SPAMMER_LIMIT to change.
        SPAMMER_LIMIT=0 means 'unlimited'

        Limit may also be set on the command-line.
        If arg#1 is an integer, the limit is set to that value
        and then the above argument rules are applied.

        Setting the environment variable 'SPAMMER_DATA' to a filename
        will cause the script to write a GraphViz graphic file.

        For the development version;
        Setting the environment variable 'SPAMMER_TRACE' to a filename
        will cause the execution engine to log a function call trace.

    _usage_statement_
    }

    # The default list of Blacklist servers:
    # Many choices, see: http://www.spews.org/lists.html

    declare -a default_servers
    # See: http://www.spamhaus.org (Conservative, well maintained)
    default_servers[0]='sbl-xbl.spamhaus.org'
    # See: http://ordb.org (Open mail relays)
    default_servers[1]='relays.ordb.org'
    # See: http://www.spamcop.net/ (You can report spammers here)
    default_servers[2]='bl.spamcop.net'
    # See: http://www.spews.org (An 'early detect' system)
    default_servers[3]='l2.spews.dnsbl.sorbs.net'
    # See: http://www.dnsbl.us.sorbs.net/using.shtml
    default_servers[4]='dnsbl.sorbs.net'
    # See: http://dsbl.org/usage (Various mail relay lists)
    default_servers[5]='list.dsbl.org'
    default_servers[6]='multihop.dsbl.org'
    default_servers[7]='unconfirmed.dsbl.org'

    # User input argument #1
    setup_input() {
        if [ -e ${1} ] && [ -r ${1} ]  # Name of readable file
        then
            file_to_array ${1} uc_name
            echo 'Using filename >'${1}'< as input.'
        else
            if is_address ${1}          # IP address?
            then
                uc_address=( ${1} )
                echo 'Starting with address >'${1}'<'
            else                       # Must be a name.
                uc_name=( ${1} )
                echo 'Starting with domain name >'${1}'<'
            fi
        fi
        return 0
    }

    # User input argument #2
    setup_servers() {
        if [ -e ${1} ] && [ -r ${1} ]  # Name of a readable file
        then
            file_to_array ${1} list_server
            echo 'Using filename >'${1}'< as blacklist server list.'
        else
            list_server=( ${1} )
            echo 'Using blacklist server >'${1}'<'
        fi
        return 0
    }

    # User environment variable SPAMMER_TRACE
    live_log_die() {
        if [ ${SPAMMER_TRACE:=} ]    # Wants trace log?
        then
            if [ ! -e ${SPAMMER_TRACE} ]
            then
                if ! touch ${SPAMMER_TRACE} 2>/dev/null
                then
                    pend_func echo $(printf '%q\n' \
                    'Unable to create log file >'${SPAMMER_TRACE}'<')
                    pend_release
                    exit 1
                fi
                _log_file=${SPAMMER_TRACE}
                _pend_hook_=trace_logger
                _log_dump=dump_log
            else
                if [ ! -w ${SPAMMER_TRACE} ]
                then
                    pend_func echo $(printf '%q\n' \
                    'Unable to write log file >'${SPAMMER_TRACE}'<')
                    pend_release
                    exit 1
                fi
                _log_file=${SPAMMER_TRACE}
                echo '' > ${_log_file}
                _pend_hook_=trace_logger
                _log_dump=dump_log
            fi
        fi
        return 0
    }

    # User environment variable SPAMMER_DATA
    data_capture() {
        if [ ${SPAMMER_DATA:=} ]    # Wants a data dump?
        then
            if [ ! -e ${SPAMMER_DATA} ]
            then
                if ! touch ${SPAMMER_DATA} 2>/dev/null
                then
                    pend_func echo $(printf '%q]n' \
                    'Unable to create data output file >'${SPAMMER_DATA}'<')
                    pend_release
                    exit 1
                fi
                _dot_file=${SPAMMER_DATA}
                _dot_dump=dump_dot
            else
                if [ ! -w ${SPAMMER_DATA} ]
                then
                    pend_func echo $(printf '%q\n' \
                    'Unable to write data output file >'${SPAMMER_DATA}'<')
                    pend_release
                    exit 1
                fi
                _dot_file=${SPAMMER_DATA}
                _dot_dump=dump_dot
            fi
        fi
        return 0
    }

    # Grope user specified arguments.
    do_user_args() {
        if [ $# -gt 0 ] && is_number $1
        then
            indirect=$1
            shift
        fi

        case $# in                     # Did user treat us well?
            1)
                if ! setup_input $1    # Needs error checking.
                then
                    pend_release
                    $_log_dump
                    exit 1
                fi
                list_server=( ${default_servers[@]} )
                _list_cnt=${#list_server[@]}
                echo 'Using default blacklist server list.'
                echo 'Search depth limit: '${indirect}
                ;;
            2)
                if ! setup_input $1    # Needs error checking.
                then
                    pend_release
                    $_log_dump
                    exit 1
                fi
                if ! setup_servers $2  # Needs error checking.
                then
                    pend_release
                    $_log_dump
                    exit 1
                fi
                echo 'Search depth limit: '${indirect}
                ;;
            *)
                pend_func usage
                pend_release
                $_log_dump
                exit 1
                ;;
        esac
        return 0
    }

    # A general purpose debug tool.
    # list_array <array_name>
    list_array() {
        [ $# -eq 1 ] || return 1  # One argument required.

        local -a _la_lines
        set -f
        local IFS=${NO_WSP}
        eval _la_lines=\(\ \$\{$1\[@\]\}\ \)
        echo
        echo "Element count "${#_la_lines[@]}" array "${1}
        local _ln_cnt=${#_la_lines[@]}

        for (( _i = 0; _i < ${_ln_cnt}; _i++ ))
        do
            echo 'Element '$_i' >'${_la_lines[$_i]}'<'
        done
        set +f
        return 0
    }

    # # # 'Hunt the Spammer' program code # # #
    pend_init                               # Ready stack engine.
    pend_func credits                       # Last thing to print.

    # # # Deal with user # # #
    live_log_die                            # Setup debug trace log.
    data_capture                            # Setup data capture file.
    echo
    do_user_args $@

    # # # Haven't exited yet - There is some hope # # #
    # Discovery group - Execution engine is LIFO - pend
    # in reverse order of execution.
    _hs_RC=0                                # Hunt the Spammer return code
    pend_mark
        pend_func report_pairs              # Report name-address pairs.

        # The two detail_* are mutually recursive functions.
        # They also pend expand_* functions as required.
        # These two (the last of ???) exit the recursion.
        pend_func detail_each_address       # Get all resources of addresses.
        pend_func detail_each_name          # Get all resources of names.

        #  The two expand_* are mutually recursive functions,
        #+ which pend additional detail_* functions as required.
        pend_func expand_input_address 1    # Expand input names by address.
        pend_func expand_input_name 1       # #xpand input addresses by name.

        # Start with a unique set of names and addresses.
        pend_func unique_lines uc_address uc_address
        pend_func unique_lines uc_name uc_name

        # Separate mixed input of names and addresses.
        pend_func split_input
    pend_release

    # # # Pairs reported -- Unique list of IP addresses found
    echo
    _ip_cnt=${#known_address[@]}
    if [ ${#list_server[@]} -eq 0 ]
    then
        echo 'Blacklist server list empty, none checked.'
    else
        if [ ${_ip_cnt} -eq 0 ]
        then
            echo 'Known address list empty, none checked.'
        else
            _ip_cnt=${_ip_cnt}-1   # Start at top.
            echo 'Checking Blacklist servers.'
            for (( _ip = _ip_cnt ; _ip >= 0 ; _ip-- ))
            do
              pend_func check_lists $( printf '%q\n' ${known_address[$_ip]} )
            done
        fi
    fi
    pend_release
    $_dot_dump                   # Graphics file dump
    $_log_dump                   # Execution trace
    echo

    ##############################
    # Example output from script #
    ##############################
    :<<-'_is_spammer_outputs_'

    ./is_spammer.bash 0 web4.alojamentos7.com

    Starting with domain name >web4.alojamentos7.com<
    Using default blacklist server list.
    Search depth limit: 0
    .:....::::...:::...:::.......::..::...:::.......::
    Known network pairs.
        66.98.208.97             web4.alojamentos7.com.
        66.98.208.97             ns1.alojamentos7.com.
        69.56.202.147            ns2.alojamentos.ws.
        66.98.208.97             alojamentos7.com.
        66.98.208.97             web.alojamentos7.com.
        69.56.202.146            ns1.alojamentos.ws.
        69.56.202.146            alojamentos.ws.
        66.235.180.113           ns1.alojamentos.org.
        66.235.181.192           ns2.alojamentos.org.
        66.235.180.113           alojamentos.org.
        66.235.180.113           web6.alojamentos.org.
        216.234.234.30           ns1.theplanet.com.
        12.96.160.115            ns2.theplanet.com.
        216.185.111.52           mail1.theplanet.com.
        69.56.141.4              spooling.theplanet.com.
        216.185.111.40           theplanet.com.
        216.185.111.40           www.theplanet.com.
        216.185.111.52           mail.theplanet.com.

    Checking Blacklist servers.
      Checking address 66.98.208.97
          Records from dnsbl.sorbs.net
      "Spam Received See: http://www.dnsbl.sorbs.net/lookup.shtml?66.98.208.97"
        Checking address 69.56.202.147
        Checking address 69.56.202.146
        Checking address 66.235.180.113
        Checking address 66.235.181.192
        Checking address 216.185.111.40
        Checking address 216.234.234.30
        Checking address 12.96.160.115
        Checking address 216.185.111.52
        Checking address 69.56.141.4

    Advanced Bash Scripting Guide: is_spammer.bash, v2, 2004-msz

    _is_spammer_outputs_

    exit ${_hs_RC}

    ####################################################
    #  The script ignores everything from here on down #
    #+ because of the 'exit' command, just above.      #
    ####################################################

    Quickstart
    ==========

     Prerequisites

      Bash version 2.05b or 3.00 (bash --version)
      A version of Bash which supports arrays. Array
      support is included by default Bash configurations.

      'dig,' version 9.x.x (dig $HOSTNAME, see first line of output)
      A version of dig which supports the +short options.
      See: dig_wrappers.bash for details.

     Optional Prerequisites

      'named,' a local DNS caching program. Any flavor will do.
      Do twice: dig $HOSTNAME
      Check near bottom of output for: SERVER: 127.0.0.1#53
      That means you have one running.

     Optional Graphics Support

      'date,' a standard *nix thing. (date -R)

      dot Program to convert graphic description file to a
      diagram. (dot -V)
      A part of the Graph-Viz set of programs.
      See: [http://www.research.att.com/sw/tools/graphviz||GraphViz]

      'dotty,' a visual editor for graphic description files.
      Also a part of the Graph-Viz set of programs.

     Quick Start

    In the same directory as the is_spammer.bash script;
    Do: ./is_spammer.bash

     Usage Details

    1. Blacklist server choices.

      (a) To use default, built-in list: Do nothing.

      (b) To use your own list:

        i. Create a file with a single Blacklist server
           domain name per line.

        ii. Provide that filename as the last argument to
            the script.

      (c) To use a single Blacklist server: Last argument
          to the script.

      (d) To disable Blacklist lookups:

        i. Create an empty file (touch spammer.nul)
           Your choice of filename.

        ii. Provide the filename of that empty file as the
            last argument to the script.

    2. Search depth limit.

      (a) To use the default value of 2: Do nothing.

      (b) To set a different limit:
          A limit of 0 means: no limit.

        i. export SPAMMER_LIMIT=1
           or whatever limit you want.

        ii. OR provide the desired limit as the first
           argument to the script.

    3. Optional execution trace log.

      (a) To use the default setting of no log output: Do nothing.

      (b) To write an execution trace log:
          export SPAMMER_TRACE=spammer.log
          or whatever filename you want.

    4. Optional graphic description file.

      (a) To use the default setting of no graphic file: Do nothing.

      (b) To write a Graph-Viz graphic description file:
          export SPAMMER_DATA=spammer.dot
          or whatever filename you want.

    5. Where to start the search.

      (a) Starting with a single domain name:

        i. Without a command-line search limit: First
           argument to script.

        ii. With a command-line search limit: Second
            argument to script.

      (b) Starting with a single IP address:

        i. Without a command-line search limit: First
           argument to script.

        ii. With a command-line search limit: Second
            argument to script.

      (c) Starting with (mixed) multiple name(s) and/or address(es):
          Create a file with one name or address per line.
          Your choice of filename.

        i. Without a command-line search limit: Filename as
           first argument to script.

        ii. With a command-line search limit: Filename as
            second argument to script.

    6. What to do with the display output.

      (a) To view display output on screen: Do nothing.

      (b) To save display output to a file: Redirect stdout to a filename.

      (c) To discard display output: Redirect stdout to /dev/null.

    7. Temporary end of decision making.
       press RETURN
       wait (optionally, watch the dots and colons).

    8. Optionally check the return code.

      (a) Return code 0: All OK

      (b) Return code 1: Script setup failure

      (c) Return code 2: Something was blacklisted.

    9. Where is my graph (diagram)?

    The script does not directly produce a graph (diagram).
    It only produces a graphic description file. You can
    process the graphic descriptor file that was output
    with the 'dot' program.

    Until you edit that descriptor file, to describe the
    relationships you want shown, all that you will get is
    a bunch of labeled name and address nodes.

    All of the script's discovered relationships are within
    a comment block in the graphic descriptor file, each
    with a descriptive heading.

    The editing required to draw a line between a pair of
    nodes from the information in the descriptor file may
    be done with a text editor.

    Given these lines somewhere in the descriptor file:

    # Known domain name nodes

    N0000 [label="guardproof.info."] ;

    N0002 [label="third.guardproof.info."] ;

    # Known address nodes

    A0000 [label="61.141.32.197"] ;

    /*

    # Known name->address edges

    NA0000 third.guardproof.info. 61.141.32.197

    # Known parent->child edges

    PC0000 guardproof.info. third.guardproof.info.

     */

    Turn that into the following lines by substituting node
    identifiers into the relationships:

    # Known domain name nodes

    N0000 [label="guardproof.info."] ;

    N0002 [label="third.guardproof.info."] ;

    # Known address nodes

    A0000 [label="61.141.32.197"] ;

    # PC0000 guardproof.info. third.guardproof.info.

    N0000->N0002 ;

    # NA0000 third.guardproof.info. 61.141.32.197

    N0002->A0000 ;

    /*

    # Known name->address edges

    NA0000 third.guardproof.info. 61.141.32.197

    # Known parent->child edges

    PC0000 guardproof.info. third.guardproof.info.

     */

    Process that with the 'dot' program, and you have your
    first network diagram.

    In addition to the conventional graphic edges, the
    descriptor file includes similar format pair-data that
    describes services, zone records (sub-graphs?),
    blacklisted addresses, and other things which might be
    interesting to include in your graph. This additional
    information could be displayed as different node
    shapes, colors, line sizes, etc.

    The descriptor file can also be read and edited by a
    Bash script (of course). You should be able to find
    most of the functions required within the
    "is_spammer.bash" script.

    # End Quickstart.

    Additional Note
    ========== ====

    Michael Zick points out that there is a "makeviz.bash" interactive
    Web site at rediris.es. Can't give the full URL, since this is not
    a publically accessible site.

Another anti-spam script.

Example A-29. Spammer Hunt

    #!/bin/bash
    # whx.sh: "whois" spammer lookup
    # Author: Walter Dnes
    # Slight revisions (first section) by ABS Guide author.
    # Used in ABS Guide with permission.

    # Needs version 3.x or greater of Bash to run (because of =~ operator).
    # Commented by script author and ABS Guide author.

    E_BADARGS=65        # Missing command-line arg.
    E_NOHOST=66         # Host not found.
    E_TIMEOUT=67        # Host lookup timed out.
    E_UNDEF=68          # Some other (undefined) error.
    HOSTWAIT=10         # Specify up to 10 seconds for host query reply.
                        # The actual wait may be a bit longer.
    OUTFILE=whois.txt   # Output file.
    PORT=4321

    if [ -z "$1" ]      # Check for (required) command-line arg.
    then
      echo "Usage: $0 domain name or IP address"
      exit $E_BADARGS
    fi

    if [[ "$1" =~ "[a-zA-Z][a-zA-Z]$" ]]  # Ends in two alpha chars?
    then                                  # It's a domain name && must do host lookup.
      IPADDR=$(host -W $HOSTWAIT $1 | awk '{print $4}')
                                          # Doing host lookup to get IP address.
    				      # Extract final field.
    else
      IPADDR="$1"                         # Command-line arg was IP address.
    fi

    echo; echo "IP Address is: "$IPADDR""; echo

    if [ -e "$OUTFILE" ]
    then
      rm -f "$OUTFILE"
      echo "Stale output file \"$OUTFILE\" removed."; echo
    fi

    #  Sanity checks.
    #  (This section needs more work.)
    #  ===============================
    if [ -z "$IPADDR" ]
    # No response.
    then
      echo "Host not found!"
      exit $E_NOHOST    # Bail out.
    fi

    if [[ "$IPADDR" =~ "^[;;]" ]]
    #  ;; connection timed out; no servers could be reached
    then
      echo "Host lookup timed out!"
      exit $E_TIMEOUT   # Bail out.
    fi

    if [[ "$IPADDR" =~ "[(NXDOMAIN)]$" ]]
    #  Host xxxxxxxxx.xxx not found: 3(NXDOMAIN)
    then
      echo "Host not found!"
      exit $E_NOHOST    # Bail out.
    fi

    if [[ "$IPADDR" =~ "[(SERVFAIL)]$" ]]
    #  Host xxxxxxxxx.xxx not found: 2(SERVFAIL)
    then
      echo "Host not found!"
      exit $E_NOHOST    # Bail out.
    fi

    # ======================== Main body of script ========================

    AFRINICquery() {
    #  Define the function that queries AFRINIC. Echo a notification to the
    #+ screen, and then run the actual query, redirecting output to $OUTFILE.

      echo "Searching for $IPADDR in whois.afrinic.net"
      whois -h whois.afrinic.net "$IPADDR" > $OUTFILE

    #  Check for presence of reference to an rwhois.
    #  Warn about non-functional rwhois.infosat.net server
    #+ and attempt rwhois query.
      if grep -e "^remarks: .*rwhois\.[^ ]\+" "$OUTFILE"
      then
        echo " " >> $OUTFILE
        echo "***" >> $OUTFILE
        echo "***" >> $OUTFILE
        echo "Warning: rwhois.infosat.net was not working as of 2005/02/02" >> $OUTFILE
        echo "         when this script was written." >> $OUTFILE
        echo "***" >> $OUTFILE
        echo "***" >> $OUTFILE
        echo " " >> $OUTFILE
        RWHOIS=`grep "^remarks: .*rwhois\.[^ ]\+" "$OUTFILE" | tail -n 1 |\
        sed "s/\(^.*\)\(rwhois\..*\)\(:4.*\)/\2/"`
        whois -h ${RWHOIS}:${PORT} "$IPADDR" >> $OUTFILE
      fi
    }

    APNICquery() {
      echo "Searching for $IPADDR in whois.apnic.net"
      whois -h whois.apnic.net "$IPADDR" > $OUTFILE

    #  Just  about  every  country has its own internet registrar.
    #  I don't normally bother consulting them, because the regional registry
    #+ usually supplies sufficient information.
    #  There are a few exceptions, where the regional registry simply
    #+ refers to the national registry for direct data.
    #  These are Japan and South Korea in APNIC, and Brasil in LACNIC.
    #  The following if statement checks $OUTFILE (whois.txt) for the presence
    #+ of "KR" (South Korea) or "JP" (Japan) in the country field.
    #  If either is found, the query is re-run against the appropriate
    #+ national registry.

      if grep -E "^country:[ ]+KR$" "$OUTFILE"
      then
        echo "Searching for $IPADDR in whois.krnic.net"
        whois -h whois.krnic.net "$IPADDR" >> $OUTFILE
      elif grep -E "^country:[ ]+JP$" "$OUTFILE"
      then
        echo "Searching for $IPADDR in whois.nic.ad.jp"
        whois -h whois.nic.ad.jp "$IPADDR"/e >> $OUTFILE
      fi
    }

    ARINquery() {
      echo "Searching for $IPADDR in whois.arin.net"
      whois -h whois.arin.net "$IPADDR" > $OUTFILE

    #  Several large internet providers listed by ARIN have their own
    #+ internal whois service, referred to as "rwhois".
    #  A large block of IP addresses is listed with the provider
    #+ under the ARIN registry.
    #  To get the IP addresses of 2nd-level ISPs or other large customers,
    #+ one has to refer to the rwhois server on port 4321.
    #  I originally started with a bunch of "if" statements checking for
    #+ the larger providers.
    #  This approach is unwieldy, and there's always another rwhois server
    #+ that I didn't know about.
    #  A more elegant approach is to check $OUTFILE for a reference
    #+ to a whois server, parse that server name out of the comment section,
    #+ and re-run the query against the appropriate rwhois server.
    #  The parsing looks a bit ugly, with a long continued line inside
    #+ backticks.
    #  But it only has to be done once, and will work as new servers are added.
    #@   ABS Guide author comment: it isn't all that ugly, and is, in fact,
    #@+  an instructive use of Regular Expressions.

      if grep -E "^Comment: .*rwhois.[^ ]+" "$OUTFILE"
      then
        RWHOIS=`grep -e "^Comment:.*rwhois\.[^ ]\+" "$OUTFILE" | tail -n 1 |\
        sed "s/^\(.*\)\(rwhois\.[^ ]\+\)\(.*$\)/\2/"`
        echo "Searching for $IPADDR in ${RWHOIS}"
        whois -h ${RWHOIS}:${PORT} "$IPADDR" >> $OUTFILE
      fi
    }

    LACNICquery() {
      echo "Searching for $IPADDR in whois.lacnic.net"
      whois -h whois.lacnic.net "$IPADDR" > $OUTFILE

    #  The  following if statement checks $OUTFILE (whois.txt) for the presence of
    #+ "BR" (Brasil) in the country field.
    #  If it is found, the query is re-run against whois.registro.br.

      if grep -E "^country:[ ]+BR$" "$OUTFILE"
      then
        echo "Searching for $IPADDR in whois.registro.br"
        whois -h whois.registro.br "$IPADDR" >> $OUTFILE
      fi
    }

    RIPEquery() {
      echo "Searching for $IPADDR in whois.ripe.net"
      whois -h whois.ripe.net "$IPADDR" > $OUTFILE
    }

    #  Initialize a few variables.
    #  * slash8 is the most significant octet
    #  * slash16 consists of the two most significant octets
    #  * octet2 is the second most significant octet

    slash8=`echo $IPADDR | cut -d. -f 1`
      if [ -z "$slash8" ]  # Yet another sanity check.
      then
        echo "Undefined error!"
        exit $E_UNDEF
      fi
    slash16=`echo $IPADDR | cut -d. -f 1-2`
    #                             ^ Period specified as 'cut" delimiter.
      if [ -z "$slash16" ]
      then
        echo "Undefined error!"
        exit $E_UNDEF
      fi
    octet2=`echo $slash16 | cut -d. -f 2`
      if [ -z "$octet2" ]
      then
        echo "Undefined error!"
        exit $E_UNDEF
      fi

    #  Check for various odds and ends of reserved space.
    #  There is no point in querying for those addresses.

    if [ $slash8 == 0 ]; then
      echo $IPADDR is '"This Network"' space\; Not querying
    elif [ $slash8 == 10 ]; then
      echo $IPADDR is RFC1918 space\; Not querying
    elif [ $slash8 == 14 ]; then
      echo $IPADDR is '"Public Data Network"' space\; Not querying
    elif [ $slash8 == 127 ]; then
      echo $IPADDR is loopback space\; Not querying
    elif [ $slash16 == 169.254 ]; then
      echo $IPADDR is link-local space\; Not querying
    elif [ $slash8 == 172 ] && [ $octet2 -ge 16 ] && [ $octet2 -le 31 ];then
      echo $IPADDR is RFC1918 space\; Not querying
    elif [ $slash16 == 192.168 ]; then
      echo $IPADDR is RFC1918 space\; Not querying
    elif [ $slash8 -ge 224 ]; then
      echo $IPADDR is either Multicast or reserved space\; Not querying
    elif [ $slash8 -ge 200 ] && [ $slash8 -le 201 ]; then LACNICquery "$IPADDR"
    elif [ $slash8 -ge 202 ] && [ $slash8 -le 203 ]; then APNICquery "$IPADDR"
    elif [ $slash8 -ge 210 ] && [ $slash8 -le 211 ]; then APNICquery "$IPADDR"
    elif [ $slash8 -ge 218 ] && [ $slash8 -le 223 ]; then APNICquery "$IPADDR"

    #  If we got this far without making a decision, query ARIN.
    #  If a reference is found in $OUTFILE to APNIC, AFRINIC, LACNIC, or RIPE,
    #+ query the appropriate whois server.

    else
      ARINquery "$IPADDR"
      if grep "whois.afrinic.net" "$OUTFILE"; then
        AFRINICquery "$IPADDR"
      elif grep -E "^OrgID:[ ]+RIPE$" "$OUTFILE"; then
        RIPEquery "$IPADDR"
      elif grep -E "^OrgID:[ ]+APNIC$" "$OUTFILE"; then
        APNICquery "$IPADDR"
      elif grep -E "^OrgID:[ ]+LACNIC$" "$OUTFILE"; then
        LACNICquery "$IPADDR"
      fi
    fi

    #@  ---------------------------------------------------------------
    #   Try also:
    #   wget http://logi.cc/nw/whois.php3?ACTION=doQuery&DOMAIN=$IPADDR
    #@  ---------------------------------------------------------------

    #  We've  now  finished  the querying.
    #  Echo a copy of the final result to the screen.

    cat $OUTFILE
    # Or "less $OUTFILE" . . .

    exit 0

    #@  ABS Guide author comments:
    #@  Nothing fancy here, but still a very useful tool for hunting spammers.
    #@  Sure, the script can be cleaned up some, and it's still a bit buggy,
    #@+ (exercise for reader), but all the same, it's a nice piece of coding
    #@+ by Walter Dnes.
    #@  Thank you!

"Little Monster's" front end to wget.

Example A-30. Making wget easier to use

    #!/bin/bash
    # wgetter2.bash

    # Author: Little Monster [monster@monstruum.co.uk]
    # ==> Used in ABS Guide with permission of script author.
    # ==> This script still needs debugging and fixups (exercise for reader).
    # ==> It could also use some additional editing in the comments.

    #  This is wgetter2 --
    #+ a Bash script to make wget a bit more friendly, and save typing.

    #  Carefully crafted by Little Monster.
    #  More or less complete on 02/02/2005.
    #  If you think this script can be improved,
    #+ email me at: monster@monstruum.co.uk
    # ==> and cc: to the author of the ABS Guide, please.
    #  This script is licenced under the GPL.
    #  You are free to copy, alter and re-use it,
    #+ but please don't try to claim you wrote it.
    #  Log your changes here instead.

    # =======================================================================
    # changelog:

    # 07/02/2005.  Fixups by Little Monster.
    # 02/02/2005.  Minor additions by Little Monster.
    #              (See after # +++++++++++ )
    # 29/01/2005.  Minor stylistic edits and cleanups by author of ABS Guide.
    #              Added exit error codes.
    # 22/11/2004.  Finished initial version of second version of wgetter:
    #              wgetter2 is born.
    # 01/12/2004.  Changed 'runn' function so it can be run 2 ways --
    #              either ask for a file name or have one input on the CL.
    # 01/12/2004.  Made sensible handling of no URL's given.
    # 01/12/2004.  Made loop of main options, so you don't
    #              have to keep calling wgetter 2 all the time.
    #              Runs as a session instead.
    # 01/12/2004.  Added looping to 'runn' function.
    #              Simplified and improved.
    # 01/12/2004.  Added state to recursion setting.
    #              Enables re-use of previous value.
    # 05/12/2004.  Modified the file detection routine in the 'runn' function
    #              so it's not fooled by empty values, and is cleaner.
    # 01/02/2004.  Added cookie finding routine from later version (which
    #              isn't ready yet), so as not to have hard-coded paths.
    # =======================================================================

    # Error codes for abnormal exit.
    E_USAGE=67        # Usage message, then quit.
    E_NO_OPTS=68      # No command-line args entered.
    E_NO_URLS=69      # No URLs passed to script.
    E_NO_SAVEFILE=70  # No save filename passed to script.
    E_USER_EXIT=71    # User decides to quit.

    #  Basic default wget command we want to use.
    #  This is the place to change it, if required.
    #  NB: if using a proxy, set http_proxy = yourproxy in .wgetrc.
    #  Otherwise delete --proxy=on, below.
    # ====================================================================
    CommandA="wget -nc -c -t 5 --progress=bar --random-wait --proxy=on -r"
    # ====================================================================

    # --------------------------------------------------------------------
    # Set some other variables and explain them.

    pattern=" -A .jpg,.JPG,.jpeg,.JPEG,.gif,.GIF,.htm,.html,.shtml,.php"
                        # wget's option to only get certain types of file.
                        # comment out if not using
    today=`date +%F`    # Used for a filename.
    home=$HOME          # Set HOME to an internal variable.
                        # In case some other path is used, change it here.
    depthDefault=3      # Set a sensible default recursion.
    Depth=$depthDefault # Otherwise user feedback doesn't tie in properly.
    RefA=""             # Set blank referring page.
    Flag=""             #  Default to not saving anything,
                        #+ or whatever else might be wanted in future.
    lister=""           # Used for passing a list of urls directly to wget.
    Woptions=""         # Used for passing wget some options for itself.
    inFile=""           # Used for the run function.
    newFile=""          # Used for the run function.
    savePath="$home/w-save"
    Config="$home/.wgetter2rc"
                        #  This is where some variables can be stored,
                        #+ if permanently changed from within the script.
    Cookie_List="$home/.cookielist"
                        # So we know where the cookies are kept . . .
    cFlag=""            # Part of the cookie file selection routine.

    # Define the options available. Easy to change letters here if needed.
    # These are the optional options; you don't just wait to be asked.

    save=s   # Save command instead of executing it.
    cook=c   # Change cookie file for this session.
    help=h   # Usage guide.
    list=l   # Pass wget the -i option and URL list.
    runn=r   # Run saved commands as an argument to the option.
    inpu=i   # Run saved commands interactively.
    wopt=w   # Allow to enter options to pass directly to wget.
    # --------------------------------------------------------------------

    if [ -z "$1" ]; then   # Make sure we get something for wget to eat.
       echo "You must at least enter a URL or option!"
       echo "-$help for usage."
       exit $E_NO_OPTS
    fi

    # +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    # added added added added added added added added added added added added

    if [ ! -e "$Config" ]; then   # See if configuration file exists.
       echo "Creating configuration file, $Config"
       echo "# This is the configuration file for wgetter2" > "$Config"
       echo "# Your customised settings will be saved in this file" >> "$Config"
    else
       source $Config             # Import variables we set outside the script.
    fi

    if [ ! -e "$Cookie_List" ]; then
       # Set up a list of cookie files, if there isn't one.
       echo "Hunting for cookies . . ."
       find -name cookies.txt >> $Cookie_List # Create the list of cookie files.
    fi #  Isolate this in its own 'if' statement,
       #+ in case we got interrupted while searching.

    if [ -z "$cFlag" ]; then # If we haven't already done this . . .
       echo                  # Make a nice space after the command prompt.
       echo "Looks like you haven't set up your source of cookies yet."
       n=0                   #  Make sure the counter
                             #+ doesn't contain random values.
       while read; do
          Cookies[$n]=$REPLY # Put the cookie files we found into an array.
          echo "$n) ${Cookies[$n]}"  # Create a menu.
          n=$(( n + 1 ))     # Increment the counter.
       done < $Cookie_List   # Feed the read statement.
       echo "Enter the number of the cookie file you want to use."
       echo "If you won't be using cookies, just press RETURN."
       echo
       echo "I won't be asking this again. Edit $Config"
       echo "If you decide to change at a later date"
       echo "or use the -${cook} option for per session changes."
       read
       if [ ! -z $REPLY ]; then   # User didn't just press return.
          Cookie=" --load-cookies ${Cookies[$REPLY]}"
          # Set the variable here as well as in the config file.

          echo "Cookie=\" --load-cookies ${Cookies[$REPLY]}\"" >> $Config
       fi
       echo "cFlag=1" >> $Config  # So we know not to ask again.
    fi

    # end added section end added section end added section end added section
    # +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    # Another variable.
    # This one may or may not be subject to variation.
    # A bit like the small print.
    CookiesON=$Cookie
    # echo "cookie file is $CookiesON" # For debugging.
    # echo "home is ${home}"           # For debugging.
                                       # Got caught with this one!

    wopts()
    {
    echo "Enter options to pass to wget."
    echo "It is assumed you know what you're doing."
    echo
    echo "You can pass their arguments here too."
    # That is to say, everything passed here is passed to wget.

    read Wopts
    # Read in the options to be passed to wget.

    Woptions=" $Wopts"
    #         ^  Why the leading space?
    # Assign to another variable.
    # Just for fun, or something . . .

    echo "passing options ${Wopts} to wget"
    # Mainly for debugging.
    # Is cute.

    return
    }

    save_func()
    {
    echo "Settings will be saved."
    if [ ! -d $savePath ]; then  #  See if directory exists.
       mkdir $savePath           #  Create the directory to save things in
                                 #+ if it isn't already there.
    fi

    Flag=S
    # Tell the final bit of code what to do.
    # Set a flag since stuff is done in main.

    return
    }

    usage() # Tell them how it works.
    {
        echo "Welcome to wgetter.  This is a front end to wget."
        echo "It will always run wget with these options:"
        echo "$CommandA"
        echo "and the pattern to match: $pattern \
    (which you can change at the top of this script)."
        echo "It will also ask you for recursion depth, \
    and if you want to use a referring page."
        echo "Wgetter accepts the following options:"
        echo ""
        echo "-$help : Display this help."
        echo "-$save : Save the command to a file $savePath/wget-($today) \
    instead of running it."
        echo "-$runn : Run saved wget commands instead of starting a new one -"
        echo "Enter filename as argument to this option."
        echo "-$inpu : Run saved wget commands interactively --"
        echo "The script will ask you for the filename."
        echo "-$cook : Change the cookies file for this session."
        echo "-$list : Tell wget to use URL's from a list instead of \
    from the command-line."
        echo "-$wopt : Pass any other options direct to wget."
        echo ""
        echo "See the wget man page for additional options \
    you can pass to wget."
        echo ""

        exit $E_USAGE  # End here. Don't process anything else.
    }

    list_func() #  Gives the user the option to use the -i option to wget,
                #+ and a list of URLs.
    {
    while [ 1 ]; do
       echo "Enter the name of the file containing URL's (press q to change
    your mind)."
       read urlfile
       if [ ! -e "$urlfile" ] && [ "$urlfile" != q ]; then
           # Look for a file, or the quit option.
           echo "That file does not exist!"
       elif [ "$urlfile" = q ]; then # Check quit option.
           echo "Not using a url list."
           return
       else
          echo "using $urlfile."
          echo "If you gave url's on the command-line, I'll use those first."
                                # Report wget standard behaviour to the user.
          lister=" -i $urlfile" # This is what we want to pass to wget.
          return
       fi
    done
    }

    cookie_func() # Give the user the option to use a different cookie file.
    {
    while [ 1 ]; do
       echo "Change the cookies file. Press return if you don't want to change
    it."
       read Cookies
       # NB: this is not the same as Cookie, earlier.
       # There is an 's' on the end.
       # Bit like chocolate chips.
       if [ -z "$Cookies" ]; then                 # Escape clause for wusses.
          return
       elif [ ! -e "$Cookies" ]; then
          echo "File does not exist.  Try again." # Keep em going . . .
       else
           CookiesON=" --load-cookies $Cookies"   # File is good -- use it!
           return
       fi
    done
    }

    run_func()
    {
    if [ -z "$OPTARG" ]; then
    # Test to see if we used the in-line option or the query one.
       if [ ! -d "$savePath" ]; then      # If directory doesn't exist . . .
          echo "$savePath does not appear to exist."
          echo "Please supply path and filename of saved wget commands:"
          read newFile
             until [ -f "$newFile" ]; do  # Keep going till we get something.
                echo "Sorry, that file does not exist.  Please try again."
                # Try really hard to get something.
                read newFile
             done

    # -----------------------------------------------------------------------
    #       if [ -z ( grep wget ${newfile} ) ]; then
            # Assume they haven't got the right file and bail out.
    #       echo "Sorry, that file does not contain wget commands.  Aborting."
    #       exit
    #       fi
    #
    # This is bogus code.
    # It doesn't actually work.
    # If anyone wants to fix it, feel free!
    # -----------------------------------------------------------------------

          filePath="${newFile}"
       else
       echo "Save path is $savePath"
         echo "Please enter name of the file which you want to use."
         echo "You have a choice of:"
         ls $savePath                                    # Give them a choice.
         read inFile
           until [ -f "$savePath/$inFile" ]; do         #  Keep going till
                                                        #+ we get something.
              if [ ! -f "${savePath}/${inFile}" ]; then # If file doesn't exist.
                 echo "Sorry, that file does not exist.  Please choose from:"
                 ls $savePath                           # If a mistake is made.
                 read inFile
              fi
             done
          filePath="${savePath}/${inFile}"  # Make one variable . . .
       fi
    else filePath="${savePath}/${OPTARG}"   # Which can be many things . . .
    fi

    if [ ! -f "$filePath" ]; then           # If a bogus file got through.
       echo "You did not specify a suitable file."
       echo "Run this script with the -${save} option first."
       echo "Aborting."
       exit $E_NO_SAVEFILE
    fi
    echo "Using: $filePath"
    while read; do
        eval $REPLY
        echo "Completed: $REPLY"
    done < $filePath  # Feed the actual file we are using into a 'while' loop.

    exit
    }

    # Fish out any options we are using for the script.
    # This is based on the demo in "Learning The Bash Shell" (O'Reilly).
    while getopts ":$save$cook$help$list$runn:$inpu$wopt" opt
    do
      case $opt in
         $save) save_func;;   #  Save some wgetter sessions for later.
         $cook) cookie_func;; #  Change cookie file.
         $help) usage;;       #  Get help.
         $list) list_func;;   #  Allow wget to use a list of URLs.
         $runn) run_func;;    #  Useful if you are calling wgetter from,
                              #+ for example, a cron script.
         $inpu) run_func;;    #  When you don't know what your files are named.
         $wopt) wopts;;       #  Pass options directly to wget.
            \?) echo "Not a valid option."
                echo "Use -${wopt} to pass options directly to wget,"
                echo "or -${help} for help";;      # Catch anything else.
      esac
    done
    shift $((OPTIND - 1))     # Do funky magic stuff with $#.

    if [ -z "$1" ] && [ -z "$lister" ]; then
                              #  We should be left with at least one URL
                              #+ on the command-line, unless a list is
    			  #+ being used -- catch empty CL's.
       echo "No URL's given! You must enter them on the same line as wgetter2."
       echo "E.g.,  wgetter2 http://somesite http://anothersite."
       echo "Use $help option for more information."
       exit $E_NO_URLS        # Bail out, with appropriate error code.
    fi

    URLS=" $@"
    # Use this so that URL list can be changed if we stay in the option loop.

    while [ 1 ]; do
       # This is where we ask for the most used options.
       # (Mostly unchanged from version 1 of wgetter)
       if [ -z $curDepth ]; then
          Current=""
       else Current=" Current value is $curDepth"
       fi
           echo "How deep should I go? \
    (integer: Default is $depthDefault.$Current)"
           read Depth   # Recursion -- how far should we go?
           inputB=""    # Reset this to blank on each pass of the loop.
           echo "Enter the name of the referring page (default is none)."
           read inputB  # Need this for some sites.

           echo "Do you want to have the output logged to the terminal"
           echo "(y/n, default is yes)?"
           read noHide  # Otherwise wget will just log it to a file.

           case $noHide in    # Now you see me, now you don't.
              y|Y ) hide="";;
              n|N ) hide=" -b";;
                * ) hide="";;
           esac

           if [ -z ${Depth} ]; then
           #  User accepted either default or current depth,
           #+ in which case Depth is now empty.
              if [ -z ${curDepth} ]; then
              #  See if a depth was set on a previous iteration.
                 Depth="$depthDefault"
                 #  Set the default recursion depth if nothing
                 #+ else to use.
              else Depth="$curDepth" #  Otherwise, set the one we used before.
              fi
           fi
       Recurse=" -l $Depth"          # Set how deep we want to go.
       curDepth=$Depth               # Remember setting for next time.

           if [ ! -z $inputB ]; then
              RefA=" --referer=$inputB"   # Option to use referring page.
           fi

       WGETTER="${CommandA}${pattern}${hide}${RefA}${Recurse}\
    ${CookiesON}${lister}${Woptions}${URLS}"
       #  Just string the whole lot together . . .
       #  NB: no embedded spaces.
       #  They are in the individual elements so that if any are empty,
       #+ we don't get an extra space.

       if [ -z "${CookiesON}" ] && [ "$cFlag" = "1" ] ; then
           echo "Warning -- can't find cookie file"
           #  This should be changed,
           #+ in case the user has opted to not use cookies.
       fi

       if [ "$Flag" = "S" ]; then
          echo "$WGETTER" >> $savePath/wget-${today}
          #  Create a unique filename for today, or append to it if it exists.
          echo "$inputB" >> $savePath/site-list-${today}
          #  Make a list, so it's easy to refer back to,
          #+ since the whole command is a bit confusing to look at.
          echo "Command saved to the file $savePath/wget-${today}"
               # Tell the user.
          echo "Referring page URL saved to the file$ \
    savePath/site-list-${today}"
               # Tell the user.
          Saver=" with save option"
          # Stick this somewhere, so it appears in the loop if set.
       else
           echo "*****************"
           echo "*****Getting*****"
           echo "*****************"
           echo ""
           echo "$WGETTER"
           echo ""
           echo "*****************"
           eval "$WGETTER"
       fi

           echo ""
           echo "Starting over$Saver."
           echo "If you want to stop, press q."
           echo "Otherwise, enter some URL's:"
           # Let them go again. Tell about save option being set.

           read
           case $REPLY in
           # Need to change this to a 'trap' clause.
              q|Q ) exit $E_USER_EXIT;;  # Exercise for the reader?
                * ) URLS=" $REPLY";;
           esac

           echo ""
    done

    exit 0

Example A-31. A podcasting script

    #!/bin/bash

    #  bashpodder.sh:
    #  By Linc 10/1/2004
    #  Find the latest script at
    #+ http://linc.homeunix.org:8080/scripts/bashpodder
    #  Last revision 12/14/2004 - Many Contributors!
    #  If you use this and have made improvements or have comments
    #+ drop me an email at linc dot fessenden at gmail dot com
    #  I'd appreciate it!

    # ==>  ABS Guide extra comments.

    # ==>  Author of this script has kindly granted permission
    # ==>+ for inclusion in ABS Guide.

    # ==> ################################################################
    #
    # ==> What is "podcasting"?

    # ==> It's broadcasting "radio shows" over the Internet.
    # ==> These shows can be played on iPods and other music file players.

    # ==> This script makes it possible.
    # ==> See documentation at the script author's site, above.

    # ==> ################################################################

    # Make script crontab friendly:
    cd $(dirname $0)
    # ==> Change to directory where this script lives.

    # datadir is the directory you want podcasts saved to:
    datadir=$(date +%Y-%m-%d)
    # ==> Will create a date-labeled directory, named: YYYY-MM-DD

    # Check for and create datadir if necessary:
    if test ! -d $datadir
            then
            mkdir $datadir
    fi

    # Delete any temp file:
    rm -f temp.log

    #  Read the bp.conf file and wget any url not already
    #+ in the podcast.log file:
    while read podcast
      do # ==> Main action follows.
      file=$(wget -q $podcast -O - | tr '\r' '\n' | tr \' \" | \
    sed -n 's/.*url="\([^"]*\)".*/\1/p')
      for url in $file
                    do
                    echo $url >> temp.log
                    if ! grep "$url" podcast.log > /dev/null
                            then
                            wget -q -P $datadir "$url"
                    fi
                    done
        done < bp.conf

    # Move dynamically created log file to permanent log file:
    cat podcast.log >> temp.log
    sort temp.log | uniq > podcast.log
    rm temp.log
    # Create an m3u playlist:
    ls $datadir | grep -v m3u > $datadir/podcast.m3u

    exit 0

    #################################################
    For a different scripting approach to Podcasting,
    see Phil Salkie's article,
    "Internet Radio to Podcast with Shell Tools"
    in the September, 2005 issue of LINUX JOURNAL,
    http://www.linuxjournal.com/article/8171
    #################################################

Example A-32. Nightly backup to a firewire HD

    #!/bin/bash
    # nightly-backup.sh
    # http://www.richardneill.org/source.php#nightly-backup-rsync
    # Copyright (c) 2005 Richard Neill <backup@richardneill.org>.
    # This is Free Software licensed under the GNU GPL.
    # ==> Included in ABS Guide with script author's kind permission.
    # ==> (Thanks!)

    #  This does a backup from the host computer to a locally connected
    #+ firewire HDD using rsync and ssh.
    #  (Script should work with USB-connected device (see lines 40-43).
    #  It then rotates the backups.
    #  Run it via cron every night at 5am.
    #  This only backs up the home directory.
    #  If ownerships (other than the user's) should be preserved,
    #+ then run the rsync process as root (and re-instate the -o).
    #  We save every day for 7 days, then every week for 4 weeks,
    #+ then every month for 3 months.

    #  See: http://www.mikerubel.org/computers/rsync_snapshots/
    #+ for more explanation of the theory.
    #  Save as: $HOME/bin/nightly-backup_firewire-hdd.sh

    #  Known bugs:
    #  ----------
    #  i)  Ideally, we want to exclude ~/.tmp and the browser caches.

    #  ii) If the user is sitting at the computer at 5am,
    #+     and files are modified while the rsync is occurring,
    #+     then the BACKUP_JUSTINCASE branch gets triggered.
    #      To some extent, this is a
    #+     feature, but it also causes a "disk-space leak".

    ##### BEGIN CONFIGURATION SECTION ############################################
    LOCAL_USER=rjn                # User whose home directory should be backed up.
    MOUNT_POINT=/backup           # Mountpoint of backup drive.
                                  # NO trailing slash!
                                  # This must be unique (eg using a udev symlink)
    # MOUNT_POINT=/media/disk     # For USB-connected device.
    SOURCE_DIR=/home/$LOCAL_USER  # NO trailing slash - it DOES matter to rsync.
    BACKUP_DEST_DIR=$MOUNT_POINT/backup/`hostname -s`.${LOCAL_USER}.nightly_backup
    DRY_RUN=false                 #If true, invoke rsync with -n, to do a dry run.
                                  # Comment out or set to false for normal use.
    VERBOSE=false                 # If true, make rsync verbose.
                                  # Comment out or set to false otherwise.
    COMPRESS=false                # If true, compress.
                                  # Good for internet, bad on LAN.
                                  # Comment out or set to false otherwise.

    ### Exit Codes ###
    E_VARS_NOT_SET=64
    E_COMMANDLINE=65
    E_MOUNT_FAIL=70
    E_NOSOURCEDIR=71
    E_UNMOUNTED=72
    E_BACKUP=73
    ##### END CONFIGURATION SECTION ##############################################

    # Check that all the important variables have been set:
    if [ -z "$LOCAL_USER" ] ||
       [ -z "$SOURCE_DIR" ] ||
       [ -z "$MOUNT_POINT" ]  ||
       [ -z "$BACKUP_DEST_DIR" ]
    then
       echo 'One of the variables is not set! Edit the file: $0. BACKUP FAILED.'
       exit $E_VARS_NOT_SET
    fi

    if [ "$#" != 0 ]  # If command-line param(s) . . .
    then              # Here document(ation).
      cat <<-ENDOFTEXT
        Automatic Nightly backup run from cron.
        Read the source for more details: $0
        The backup directory is $BACKUP_DEST_DIR .
        It will be created if necessary; initialisation is no longer required.

        WARNING: Contents of $BACKUP_DEST_DIR are rotated.
        Directories named 'backup.\$i' will eventually be DELETED.
        We keep backups from every day for 7 days (1-8),
        then every week for 4 weeks (9-12),
        then every month for 3 months (13-15).

        You may wish to add this to your crontab using 'crontab -e'
        #  Back up files: $SOURCE_DIR to $BACKUP_DEST_DIR
        #+ every night at 3:15 am
             15 03 * * * /home/$LOCAL_USER/bin/nightly-backup_firewire-hdd.sh

        Don't forget to verify the backups are working,
        especially if you don't read cron's mail!"
    	ENDOFTEXT
       exit $E_COMMANDLINE
    fi

    # Parse the options.
    # ==================

    if [ "$DRY_RUN" == "true" ]; then
      DRY_RUN="-n"
      echo "WARNING:"
      echo "THIS IS A 'DRY RUN'!"
      echo "No data will actually be transferred!"
    else
      DRY_RUN=""
    fi

    if [ "$VERBOSE" == "true" ]; then
      VERBOSE="-v"
    else
      VERBOSE=""
    fi

    if [ "$COMPRESS" == "true" ]; then
      COMPRESS="-z"
    else
      COMPRESS=""
    fi

    #  Every week (actually of 8 days) and every month,
    #+ extra backups are preserved.
    DAY_OF_MONTH=`date +%d`            # Day of month (01..31).
    if [ $DAY_OF_MONTH = 01 ]; then    # First of month.
      MONTHSTART=true
    elif [ $DAY_OF_MONTH = 08 \
        -o $DAY_OF_MONTH = 16 \
        -o $DAY_OF_MONTH = 24 ]; then
        # Day 8,16,24  (use 8, not 7 to better handle 31-day months)
          WEEKSTART=true
    fi

    #  Check that the HDD is mounted.
    #  At least, check that *something* is mounted here!
    #  We can use something unique to the device, rather than just guessing
    #+ the scsi-id by having an appropriate udev rule in
    #+ /etc/udev/rules.d/10-rules.local
    #+ and by putting a relevant entry in /etc/fstab.
    #  Eg: this udev rule:
    # BUS="scsi", KERNEL="sd*", SYSFS{vendor}="WDC WD16",
    # SYSFS{model}="00JB-00GVA0     ", NAME="%k", SYMLINK="lacie_1394d%n"

    if mount | grep $MOUNT_POINT >/dev/null; then
      echo "Mount point $MOUNT_POINT is indeed mounted. OK"
    else
      echo -n "Attempting to mount $MOUNT_POINT..."
               # If it isn't mounted, try to mount it.
      sudo mount $MOUNT_POINT 2>/dev/null

      if mount | grep $MOUNT_POINT >/dev/null; then
        UNMOUNT_LATER=TRUE
        echo "OK"
        #  Note: Ensure that this is also unmounted
        #+ if we exit prematurely with failure.
      else
        echo "FAILED"
        echo -e "Nothing is mounted at $MOUNT_POINT. BACKUP FAILED!"
        exit $E_MOUNT_FAIL
      fi
    fi

    # Check that source dir exists and is readable.
    if [ ! -r  $SOURCE_DIR ] ; then
      echo "$SOURCE_DIR does not exist, or cannot be read. BACKUP FAILED."
      exit $E_NOSOURCEDIR
    fi

    # Check that the backup directory structure is as it should be.
    # If not, create it.
    # Create the subdirectories.
    # Note that backup.0 will be created as needed by rsync.

    for ((i=1;i<=15;i++)); do
      if [ ! -d $BACKUP_DEST_DIR/backup.$i ]; then
        if /bin/mkdir -p $BACKUP_DEST_DIR/backup.$i ; then
        #  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  No [ ] test brackets. Why?
          echo "Warning: directory $BACKUP_DEST_DIR/backup.$i is missing,"
          echo "or was not initialised. (Re-)creating it."
        else
          echo "ERROR: directory $BACKUP_DEST_DIR/backup.$i"
          echo "is missing and could not be created."
        if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
            # Before we exit, unmount the mount point if necessary.
            cd
    	sudo umount $MOUNT_POINT &&
    	echo "Unmounted $MOUNT_POINT again. Giving up."
        fi
          exit $E_UNMOUNTED
      fi
    fi
    done

    #  Set the permission to 700 for security
    #+ on an otherwise permissive multi-user system.
    if ! /bin/chmod 700 $BACKUP_DEST_DIR ; then
      echo "ERROR: Could not set permissions on $BACKUP_DEST_DIR to 700."

      if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
      # Before we exit, unmount the mount point if necessary.
         cd ; sudo umount $MOUNT_POINT \
         && echo "Unmounted $MOUNT_POINT again. Giving up."
      fi

      exit $E_UNMOUNTED
    fi

    # Create the symlink: current -> backup.1 if required.
    # A failure here is not critical.
    cd $BACKUP_DEST_DIR
    if [ ! -h current ] ; then
      if ! /bin/ln -s backup.1 current ; then
        echo "WARNING: could not create symlink current -> backup.1"
      fi
    fi

    # Now, do the rsync.
    echo "Now doing backup with rsync..."
    echo "Source dir: $SOURCE_DIR"
    echo -e "Backup destination dir: $BACKUP_DEST_DIR\n"

    /usr/bin/rsync $DRY_RUN $VERBOSE -a -S --delete --modify-window=60 \
    --link-dest=../backup.1 $SOURCE_DIR $BACKUP_DEST_DIR/backup.0/

    #  Only warn, rather than exit if the rsync failed,
    #+ since it may only be a minor problem.
    #  E.g., if one file is not readable, rsync will fail.
    #  This shouldn't prevent the rotation.
    #  Not using, e.g., `date +%a`  since these directories
    #+ are just full of links and don't consume *that much* space.

    if [ $? != 0 ]; then
      BACKUP_JUSTINCASE=backup.`date +%F_%T`.justincase
      echo "WARNING: the rsync process did not entirely succeed."
      echo "Something might be wrong."
      echo "Saving an extra copy at: $BACKUP_JUSTINCASE"
      echo "WARNING: if this occurs regularly, a LOT of space will be consumed,"
      echo "even though these are just hard-links!"
    fi

    # Save a readme in the backup parent directory.
    # Save another one in the recent subdirectory.
    echo "Backup of $SOURCE_DIR on `hostname` was last run on \
    `date`" > $BACKUP_DEST_DIR/README.txt
    echo "This backup of $SOURCE_DIR on `hostname` was created on \
    `date`" > $BACKUP_DEST_DIR/backup.0/README.txt

    # If we are not in a dry run, rotate the backups.
    [ -z "$DRY_RUN" ] &&

      #  Check how full the backup disk is.
      #  Warn if 90%. if 98% or more, we'll probably fail, so give up.
      #  (Note: df can output to more than one line.)
      #  We test this here, rather than before
      #+ so that rsync may possibly have a chance.
      DISK_FULL_PERCENT=`/bin/df $BACKUP_DEST_DIR |
      tr "\n" ' ' | awk '{print $12}' | grep -oE [0-9]+ `
      echo "Disk space check on backup partition \
      $MOUNT_POINT $DISK_FULL_PERCENT% full."
      if [ $DISK_FULL_PERCENT -gt 90 ]; then
        echo "Warning: Disk is greater than 90% full."
      fi
      if [ $DISK_FULL_PERCENT -gt 98 ]; then
        echo "Error: Disk is full! Giving up."
          if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
            # Before we exit, unmount the mount point if necessary.
            cd; sudo umount $MOUNT_POINT &&
            echo "Unmounted $MOUNT_POINT again. Giving up."
          fi
        exit $E_UNMOUNTED
      fi

     # Create an extra backup.
     # If this copy fails, give up.
     if [ -n "$BACKUP_JUSTINCASE" ]; then
       if ! /bin/cp -al $BACKUP_DEST_DIR/backup.0 \
          $BACKUP_DEST_DIR/$BACKUP_JUSTINCASE
       then
         echo "ERROR: Failed to create extra copy \
         $BACKUP_DEST_DIR/$BACKUP_JUSTINCASE"
         if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
           # Before we exit, unmount the mount point if necessary.
           cd ;sudo umount $MOUNT_POINT &&
           echo "Unmounted $MOUNT_POINT again. Giving up."
         fi
         exit $E_UNMOUNTED
       fi
     fi

     # At start of month, rotate the oldest 8.
     if [ "$MONTHSTART" == "true" ]; then
       echo -e "\nStart of month. \
       Removing oldest backup: $BACKUP_DEST_DIR/backup.15"  &&
       /bin/rm -rf  $BACKUP_DEST_DIR/backup.15  &&
       echo "Rotating monthly,weekly backups: \
       $BACKUP_DEST_DIR/backup.[8-14] -> $BACKUP_DEST_DIR/backup.[9-15]"  &&
         /bin/mv $BACKUP_DEST_DIR/backup.14 $BACKUP_DEST_DIR/backup.15  &&
         /bin/mv $BACKUP_DEST_DIR/backup.13 $BACKUP_DEST_DIR/backup.14  &&
         /bin/mv $BACKUP_DEST_DIR/backup.12 $BACKUP_DEST_DIR/backup.13  &&
         /bin/mv $BACKUP_DEST_DIR/backup.11 $BACKUP_DEST_DIR/backup.12  &&
         /bin/mv $BACKUP_DEST_DIR/backup.10 $BACKUP_DEST_DIR/backup.11  &&
         /bin/mv $BACKUP_DEST_DIR/backup.9 $BACKUP_DEST_DIR/backup.10  &&
         /bin/mv $BACKUP_DEST_DIR/backup.8 $BACKUP_DEST_DIR/backup.9

     # At start of week, rotate the second-oldest 4.
     elif [ "$WEEKSTART" == "true" ]; then
       echo -e "\nStart of week. \
       Removing oldest weekly backup: $BACKUP_DEST_DIR/backup.12"  &&
       /bin/rm -rf  $BACKUP_DEST_DIR/backup.12  &&

       echo "Rotating weekly backups: \
       $BACKUP_DEST_DIR/backup.[8-11] -> $BACKUP_DEST_DIR/backup.[9-12]"  &&
         /bin/mv $BACKUP_DEST_DIR/backup.11 $BACKUP_DEST_DIR/backup.12  &&
         /bin/mv $BACKUP_DEST_DIR/backup.10 $BACKUP_DEST_DIR/backup.11  &&
         /bin/mv $BACKUP_DEST_DIR/backup.9 $BACKUP_DEST_DIR/backup.10  &&
         /bin/mv $BACKUP_DEST_DIR/backup.8 $BACKUP_DEST_DIR/backup.9

     else
       echo -e "\nRemoving oldest daily backup: $BACKUP_DEST_DIR/backup.8"  &&
         /bin/rm -rf  $BACKUP_DEST_DIR/backup.8

     fi  &&

     # Every day, rotate the newest 8.
     echo "Rotating daily backups: \
     $BACKUP_DEST_DIR/backup.[1-7] -> $BACKUP_DEST_DIR/backup.[2-8]"  &&
         /bin/mv $BACKUP_DEST_DIR/backup.7 $BACKUP_DEST_DIR/backup.8  &&
         /bin/mv $BACKUP_DEST_DIR/backup.6 $BACKUP_DEST_DIR/backup.7  &&
         /bin/mv $BACKUP_DEST_DIR/backup.5 $BACKUP_DEST_DIR/backup.6  &&
         /bin/mv $BACKUP_DEST_DIR/backup.4 $BACKUP_DEST_DIR/backup.5  &&
         /bin/mv $BACKUP_DEST_DIR/backup.3 $BACKUP_DEST_DIR/backup.4  &&
         /bin/mv $BACKUP_DEST_DIR/backup.2 $BACKUP_DEST_DIR/backup.3  &&
         /bin/mv $BACKUP_DEST_DIR/backup.1 $BACKUP_DEST_DIR/backup.2  &&
         /bin/mv $BACKUP_DEST_DIR/backup.0 $BACKUP_DEST_DIR/backup.1  &&

     SUCCESS=true

    if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
      # Unmount the mount point if it wasn't mounted to begin with.
      cd ; sudo umount $MOUNT_POINT && echo "Unmounted $MOUNT_POINT again."
    fi

    if [ "$SUCCESS" == "true" ]; then
      echo 'SUCCESS!'
      exit 0
    fi

    # Should have already exited if backup worked.
    echo 'BACKUP FAILED! Is this just a dry run? Is the disk full?) '
    exit $E_BACKUP

Example A-33. An expanded cd command

    ###########################################################################
    #
    #       cdll
    #       by Phil Braham
    #
    #       ############################################
    #       Latest version of this script available from
    #       http://freshmeat.net/projects/cd/
    #       ############################################
    #
    #       .cd_new
    #
    #       An enhancement of the Unix cd command
    #
    #       There are unlimited stack entries and special entries. The stack
    #       entries keep the last cd_maxhistory
    #       directories that have been used. The special entries can be
    #       assigned to commonly used directories.
    #
    #       The special entries may be pre-assigned by setting the environment
    #       variables CDSn or by using the -u or -U command.
    #
    #       The following is a suggestion for the .profile file:
    #
    #               . cdll              #  Set up the cd command
    #       alias cd='cd_new'           #  Replace the cd command
    #               cd -U               #  Upload pre-assigned entries for
    #                                   #+ the stack and special entries
    #               cd -D               #  Set non-default mode
    #               alias @="cd_new @"  #  Allow @ to be used to get history
    #
    #       For help type:
    #
    #               cd -h or
    #               cd -H
    #
    #
    ###########################################################################
    #
    #       Version 1.2.1
    #
    #       Written by Phil Braham - Realtime Software Pty Ltd
    #       (realtime@mpx.com.au)
    #       Please send any suggestions or enhancements to the author (also at
    #       phil@braham.net)
    #
    ############################################################################

    cd_hm ()
    {
            ${PRINTF} "%s" "cd [dir] [0-9] [@[s|h] [-g [<dir>]] [-d] \
    [-D] [-r<n>] [dir|0-9] [-R<n>] [<dir>|0-9]
       [-s<n>] [-S<n>] [-u] [-U] [-f] [-F] [-h] [-H] [-v]
        <dir> Go to directory
        0-n         Go to previous directory (0 is previous, 1 is last but 1 etc)
                    n is up to max history (default is 50)
        @           List history and special entries
        @h          List history entries
        @s          List special entries
        -g [<dir>]  Go to literal name (bypass special names)
                    This is to allow access to dirs called '0','1','-h' etc
        -d          Change default action - verbose. (See note)
        -D          Change default action - silent. (See note)
        -s<n> Go to the special entry <n>*
        -S<n> Go to the special entry <n>
                    and replace it with the current dir*
        -r<n> [<dir>] Go to directory <dir>
                                  and then put it on special entry <n>*
        -R<n> [<dir>] Go to directory <dir>
                                  and put current dir on special entry <n>*
        -a<n>       Alternative suggested directory. See note below.
        -f [<file>] File entries to <file>.
        -u [<file>] Update entries from <file>.
                    If no filename supplied then default file
                    (${CDPath}${2:-"$CDFile"}) is used
                    -F and -U are silent versions
        -v          Print version number
        -h          Help
        -H          Detailed help

        *The special entries (0 - 9) are held until log off, replaced by another
         entry or updated with the -u command

        Alternative suggested directories:
        If a directory is not found then CD will suggest any
        possibilities. These are directories starting with the same letters
        and if any are found they are listed prefixed with -a<n>
        where <n> is a number.
        It's possible to go to the directory by entering cd -a<n>
        on the command line.

        The directory for -r<n> or -R<n> may be a number.
        For example:
            $ cd -r3 4  Go to history entry 4 and put it on special entry 3
            $ cd -R3 4  Put current dir on the special entry 3
                        and go to history entry 4
            $ cd -s3    Go to special entry 3

        Note that commands R,r,S and s may be used without a number
        and refer to 0:
            $ cd -s     Go to special entry 0
            $ cd -S     Go to special entry 0 and make special
                        entry 0 current dir
            $ cd -r 1   Go to history entry 1 and put it on special entry 0
            $ cd -r     Go to history entry 0 and put it on special entry 0
        "
            if ${TEST} "$CD_MODE" = "PREV"
            then
                    ${PRINTF} "$cd_mnset"
            else
                    ${PRINTF} "$cd_mset"
            fi
    }

    cd_Hm ()
    {
            cd_hm
            ${PRINTF} "%s" "
            The previous directories (0-$cd_maxhistory) are stored in the
            environment variables CD[0] - CD[$cd_maxhistory]
            Similarly the special directories S0 - $cd_maxspecial are in
            the environment variable CDS[0] - CDS[$cd_maxspecial]
            and may be accessed from the command line

            The default pathname for the -f and -u commands is $CDPath
            The default filename for the -f and -u commands is $CDFile

            Set the following environment variables:
                CDL_PROMPTLEN  - Set to the length of prompt you require.
                    Prompt string is set to the right characters of the
                    current directory.
                    If not set then prompt is left unchanged
                CDL_PROMPT_PRE - Set to the string to prefix the prompt.
                    Default is:
                        non-root:  \"\\[\\e[01;34m\\]\"  (sets colour to blue).
                        root:      \"\\[\\e[01;31m\\]\"  (sets colour to red).
                CDL_PROMPT_POST    - Set to the string to suffix the prompt.
                    Default is:
                        non-root:  \"\\[\\e[00m\\]$\"
                                    (resets colour and displays $).
                        root:      \"\\[\\e[00m\\]#\"
                                    (resets colour and displays #).
                CDPath - Set the default path for the -f & -u options.
                         Default is home directory
                CDFile - Set the default filename for the -f & -u options.
                         Default is cdfile

    "
        cd_version

    }

    cd_version ()
    {
     printf "Version: ${VERSION_MAJOR}.${VERSION_MINOR} Date: ${VERSION_DATE}\n"
    }

    #
    # Truncate right.
    #
    # params:
    #   p1 - string
    #   p2 - length to truncate to
    #
    # returns string in tcd
    #
    cd_right_trunc ()
    {
        local tlen=${2}
        local plen=${#1}
        local str="${1}"
        local diff
        local filler="<--"
        if ${TEST} ${plen} -le ${tlen}
        then
            tcd="${str}"
        else
            let diff=${plen}-${tlen}
            elen=3
            if ${TEST} ${diff} -le 2
            then
                let elen=${diff}
            fi
            tlen=-${tlen}
            let tlen=${tlen}+${elen}
            tcd=${filler:0:elen}${str:tlen}
        fi
    }

    #
    # Three versions of do history:
    #    cd_dohistory  - packs history and specials side by side
    #    cd_dohistoryH - Shows only hstory
    #    cd_dohistoryS - Shows only specials
    #
    cd_dohistory ()
    {
        cd_getrc
            ${PRINTF} "History:\n"
        local -i count=${cd_histcount}
        while ${TEST} ${count} -ge 0
        do
            cd_right_trunc "${CD[count]}" ${cd_lchar}
                ${PRINTF} "%2d %-${cd_lchar}.${cd_lchar}s " ${count} "${tcd}"

            cd_right_trunc "${CDS[count]}" ${cd_rchar}
                ${PRINTF} "S%d %-${cd_rchar}.${cd_rchar}s\n" ${count} "${tcd}"
            count=${count}-1
        done
    }

    cd_dohistoryH ()
    {
        cd_getrc
            ${PRINTF} "History:\n"
            local -i count=${cd_maxhistory}
            while ${TEST} ${count} -ge 0
            do
              ${PRINTF} "${count} %-${cd_flchar}.${cd_flchar}s\n" ${CD[$count]}
              count=${count}-1
            done
    }

    cd_dohistoryS ()
    {
        cd_getrc
            ${PRINTF} "Specials:\n"
            local -i count=${cd_maxspecial}
            while ${TEST} ${count} -ge 0
            do
              ${PRINTF} "S${count} %-${cd_flchar}.${cd_flchar}s\n" ${CDS[$count]}
              count=${count}-1
            done
    }

    cd_getrc ()
    {
        cd_flchar=$(stty -a | awk -F \;
        '/rows/ { print $2 $3 }' | awk -F \  '{ print $4 }')
        if ${TEST} ${cd_flchar} -ne 0
        then
            cd_lchar=${cd_flchar}/2-5
            cd_rchar=${cd_flchar}/2-5
                cd_flchar=${cd_flchar}-5
        else
                cd_flchar=${FLCHAR:=75}
    	    # cd_flchar is used for for the @s & @h history
                cd_lchar=${LCHAR:=35}
                cd_rchar=${RCHAR:=35}
        fi
    }

    cd_doselection ()
    {
            local -i nm=0
            cd_doflag="TRUE"
            if ${TEST} "${CD_MODE}" = "PREV"
            then
                    if ${TEST} -z "$cd_npwd"
                    then
                            cd_npwd=0
                    fi
            fi
            tm=$(echo "${cd_npwd}" | cut -b 1)
        if ${TEST} "${tm}" = "-"
        then
            pm=$(echo "${cd_npwd}" | cut -b 2)
            nm=$(echo "${cd_npwd}" | cut -d $pm -f2)
            case "${pm}" in
                 a) cd_npwd=${cd_sugg[$nm]} ;;
                 s) cd_npwd="${CDS[$nm]}" ;;
                 S) cd_npwd="${CDS[$nm]}" ; CDS[$nm]=`pwd` ;;
                 r) cd_npwd="$2" ; cd_specDir=$nm ; cd_doselection "$1" "$2";;
                 R) cd_npwd="$2" ; CDS[$nm]=`pwd` ; cd_doselection "$1" "$2";;
            esac
        fi

        if ${TEST} "${cd_npwd}" != "." -a "${cd_npwd}" \
    != ".." -a "${cd_npwd}" -le ${cd_maxhistory} >>/dev/null 2>&1
        then
          cd_npwd=${CD[$cd_npwd]}
         else
           case "$cd_npwd" in
                    @)  cd_dohistory ; cd_doflag="FALSE" ;;
                   @h) cd_dohistoryH ; cd_doflag="FALSE" ;;
                   @s) cd_dohistoryS ; cd_doflag="FALSE" ;;
                   -h) cd_hm ; cd_doflag="FALSE" ;;
                   -H) cd_Hm ; cd_doflag="FALSE" ;;
                   -f) cd_fsave "SHOW" $2 ; cd_doflag="FALSE" ;;
                   -u) cd_upload "SHOW" $2 ; cd_doflag="FALSE" ;;
                   -F) cd_fsave "NOSHOW" $2 ; cd_doflag="FALSE" ;;
                   -U) cd_upload "NOSHOW" $2 ; cd_doflag="FALSE" ;;
                   -g) cd_npwd="$2" ;;
                   -d) cd_chdefm 1; cd_doflag="FALSE" ;;
                   -D) cd_chdefm 0; cd_doflag="FALSE" ;;
                   -r) cd_npwd="$2" ; cd_specDir=0 ; cd_doselection "$1" "$2";;
                   -R) cd_npwd="$2" ; CDS[0]=`pwd` ; cd_doselection "$1" "$2";;
                   -s) cd_npwd="${CDS[0]}" ;;
                   -S) cd_npwd="${CDS[0]}"  ; CDS[0]=`pwd` ;;
                   -v) cd_version ; cd_doflag="FALSE";;
           esac
        fi
    }

    cd_chdefm ()
    {
            if ${TEST} "${CD_MODE}" = "PREV"
            then
                    CD_MODE=""
                    if ${TEST} $1 -eq 1
                    then
                            ${PRINTF} "${cd_mset}"
                    fi
            else
                    CD_MODE="PREV"
                    if ${TEST} $1 -eq 1
                    then
                            ${PRINTF} "${cd_mnset}"
                    fi
            fi
    }

    cd_fsave ()
    {
            local sfile=${CDPath}${2:-"$CDFile"}
            if ${TEST} "$1" = "SHOW"
            then
                    ${PRINTF} "Saved to %s\n" $sfile
            fi
            ${RM} -f ${sfile}
            local -i count=0
            while ${TEST} ${count} -le ${cd_maxhistory}
            do
                    echo "CD[$count]=\"${CD[$count]}\"" >> ${sfile}
                    count=${count}+1
            done
            count=0
            while ${TEST} ${count} -le ${cd_maxspecial}
            do
                    echo "CDS[$count]=\"${CDS[$count]}\"" >> ${sfile}
                    count=${count}+1
            done
    }

    cd_upload ()
    {
            local sfile=${CDPath}${2:-"$CDFile"}
            if ${TEST} "${1}" = "SHOW"
            then
                    ${PRINTF} "Loading from %s\n" ${sfile}
            fi
            . ${sfile}
    }

    cd_new ()
    {
        local -i count
        local -i choose=0

            cd_npwd="${1}"
            cd_specDir=-1
            cd_doselection "${1}" "${2}"

            if ${TEST} ${cd_doflag} = "TRUE"
            then
                    if ${TEST} "${CD[0]}" != "`pwd`"
                    then
                            count=$cd_maxhistory
                            while ${TEST} $count -gt 0
                            do
                                    CD[$count]=${CD[$count-1]}
                                    count=${count}-1
                            done
                            CD[0]=`pwd`
                    fi
                    command cd "${cd_npwd}" 2>/dev/null
            if ${TEST} $? -eq 1
            then
                ${PRINTF} "Unknown dir: %s\n" "${cd_npwd}"
                local -i ftflag=0
                for i in "${cd_npwd}"*
                do
                    if ${TEST} -d "${i}"
                    then
                        if ${TEST} ${ftflag} -eq 0
                        then
                            ${PRINTF} "Suggest:\n"
                            ftflag=1
                    fi
                        ${PRINTF} "\t-a${choose} %s\n" "$i"
                                            cd_sugg[$choose]="${i}"
                        choose=${choose}+1
            fi
                done
            fi
            fi

            if ${TEST} ${cd_specDir} -ne -1
            then
                    CDS[${cd_specDir}]=`pwd`
            fi

            if ${TEST} ! -z "${CDL_PROMPTLEN}"
            then
            cd_right_trunc "${PWD}" ${CDL_PROMPTLEN}
                cd_rp=${CDL_PROMPT_PRE}${tcd}${CDL_PROMPT_POST}
                    export PS1="$(echo -ne ${cd_rp})"
            fi
    }
    #########################################################################
    #                                                                       #
    #                        Initialisation here                            #
    #                                                                       #
    #########################################################################
    #
    VERSION_MAJOR="1"
    VERSION_MINOR="2.1"
    VERSION_DATE="24-MAY-2003"
    #
    alias cd=cd_new
    #
    # Set up commands
    RM=/bin/rm
    TEST=test
    PRINTF=printf              # Use builtin printf

    #########################################################################
    #                                                                       #
    # Change this to modify the default pre- and post prompt strings.       #
    # These only come into effect if CDL_PROMPTLEN is set.                  #
    #                                                                       #
    #########################################################################
    if ${TEST} ${EUID} -eq 0
    then
    #   CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="$HOSTNAME@"}
        CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="\\[\\e[01;31m\\]"}  # Root is in red
        CDL_PROMPT_POST=${CDL_PROMPT_POST:="\\[\\e[00m\\]#"}
    else
        CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="\\[\\e[01;34m\\]"}  # Users in blue
        CDL_PROMPT_POST=${CDL_PROMPT_POST:="\\[\\e[00m\\]$"}
    fi
    #########################################################################
    #
    # cd_maxhistory defines the max number of history entries allowed.
    typeset -i cd_maxhistory=50

    #########################################################################
    #
    # cd_maxspecial defines the number of special entries.
    typeset -i cd_maxspecial=9
    #
    #
    #########################################################################
    #
    #  cd_histcount defines the number of entries displayed in
    #+ the history command.
    typeset -i cd_histcount=9
    #
    #########################################################################
    export CDPath=${HOME}/
    #  Change these to use a different                                      #
    #+ default path and filename                                            #
    export CDFile=${CDFILE:=cdfile}           # for the -u and -f commands  #
    #
    #########################################################################
                                                                            #
    typeset -i cd_lchar cd_rchar cd_flchar
                            #  This is the number of chars to allow for the #
    cd_flchar=${FLCHAR:=75} #+ cd_flchar is used for for the @s & @h history#

    typeset -ax CD CDS
    #
    cd_mset="\n\tDefault mode is now set - entering cd with no parameters \
    has the default action\n\tUse cd -d or -D for cd to go to \
    previous directory with no parameters\n"
    cd_mnset="\n\tNon-default mode is now set - entering cd with no \
    parameters is the same as entering cd 0\n\tUse cd -d or \
    -D to change default cd action\n"

    # ==================================================================== #

    : <<DOCUMENTATION

    Written by Phil Braham. Realtime Software Pty Ltd.
    Released under GNU license. Free to use. Please pass any modifications
    or comments to the author Phil Braham:

    realtime@mpx.com.au
    =======================================================================

    cdll is a replacement for cd and incorporates similar functionality to
    the bash pushd and popd commands but is independent of them.

    This version of cdll has been tested on Linux using Bash. It will work
    on most Linux versions but will probably not work on other shells without
    modification.

    Introduction
    ============

    cdll allows easy moving about between directories. When changing to a new
    directory the current one is automatically put onto a stack. By default
    50 entries are kept, but this is configurable. Special directories can be
    kept for easy access - by default up to 10, but this is configurable. The
    most recent stack entries and the special entries can be easily viewed.

    The directory stack and special entries can be saved to, and loaded from,
    a file. This allows them to be set up on login, saved before logging out
    or changed when moving project to project.

    In addition, cdll provides a flexible command prompt facility that allows,
    for example, a directory name in colour that is truncated from the left
    if it gets too long.

    Setting up cdll
    ===============

    Copy cdll to either your local home directory or a central directory
    such as /usr/bin (this will require root access).

    Copy the file cdfile to your home directory. It will require read and
    write access. This a default file that contains a directory stack and
    special entries.

    To replace the cd command you must add commands to your login script.
    The login script is one or more of:

        /etc/profile
        ~/.bash_profile
        ~/.bash_login
        ~/.profile
        ~/.bashrc
        /etc/bash.bashrc.local

    To setup your login, ~/.bashrc is recommended, for global (and root) setup
    add the commands to /etc/bash.bashrc.local

    To set up on login, add the command:
        . <dir>/cdll
    For example if cdll is in your local home directory:
        . ~/cdll
    If in /usr/bin then:
        . /usr/bin/cdll

    If you want to use this instead of the buitin cd command then add:
        alias cd='cd_new'
    We would also recommend the following commands:
        alias @='cd_new @'
        cd -U
        cd -D

    If you want to use cdll's prompt facilty then add the following:
        CDL_PROMPTLEN=nn
    Where nn is a number described below. Initially 99 would be suitable
    number.

    Thus the script looks something like this:

        ######################################################################
        # CD Setup
        ######################################################################
        CDL_PROMPTLEN=21        # Allow a prompt length of up to 21 characters
        . /usr/bin/cdll         # Initialise cdll
        alias cd='cd_new'       # Replace the built in cd command
        alias @='cd_new @'      # Allow @ at the prompt to display history
        cd -U                   # Upload directories
        cd -D                   # Set default action to non-posix
        ######################################################################

    The full meaning of these commands will become clear later.

    There are a couple of caveats. If another program changes the directory
    without calling cdll, then the directory won't be put on the stack and
    also if the prompt facility is used then this will not be updated. Two
    programs that can do this are pushd and popd. To update the prompt and
    stack simply enter:

        cd .

    Note that if the previous entry on the stack is the current directory
    then the stack is not updated.

    Usage
    =====
    cd [dir] [0-9] [@[s|h] [-g <dir>] [-d] [-D] [-r<n>]
       [dir|0-9] [-R<n>] [<dir>|0-9] [-s<n>] [-S<n>]
       [-u] [-U] [-f] [-F] [-h] [-H] [-v]

        <dir>       Go to directory
        0-n         Goto previous directory (0 is previous,
                    1 is last but 1, etc.)
                    n is up to max history (default is 50)
        @           List history and special entries (Usually available as $ @)
        @h          List history entries
        @s          List special entries
        -g [<dir>]  Go to literal name (bypass special names)
                    This is to allow access to dirs called '0','1','-h' etc
        -d          Change default action - verbose. (See note)
        -D          Change default action - silent. (See note)
        -s<n>       Go to the special entry <n>
        -S<n>       Go to the special entry <n>
                          and replace it with the current dir
        -r<n> [<dir>] Go to directory <dir>
                                  and then put it on special entry <n>
        -R<n> [<dir>] Go to directory <dir>
                                  and put current dir on special entry <n>
        -a<n>       Alternative suggested directory. See note below.
        -f [<file>] File entries to <file>.
        -u [<file>] Update entries from <file>.
                    If no filename supplied then default file (~/cdfile) is used
                    -F and -U are silent versions
        -v          Print version number
        -h          Help
        -H          Detailed help

    Examples
    ========

    These examples assume non-default mode is set (that is, cd with no
    parameters will go to the most recent stack directory), that aliases
    have been set up for cd and @ as described above and that cd's prompt
    facility is active and the prompt length is 21 characters.

        /home/phil$ @
        # List the entries with the @
        History:
        # Output of the @ command
        .....
        # Skipped these entries for brevity
        1 /home/phil/ummdev               S1 /home/phil/perl
        # Most recent two history entries
        0 /home/phil/perl/eg              S0 /home/phil/umm/ummdev
        # and two special entries are shown

        /home/phil$ cd /home/phil/utils/Cdll
        # Now change directories
        /home/phil/utils/Cdll$ @
        # Prompt reflects the directory.
        History:
        # New history
        .....
        1 /home/phil/perl/eg              S1 /home/phil/perl
        # History entry 0 has moved to 1
        0 /home/phil                      S0 /home/phil/umm/ummdev
        # and the most recent has entered

    To go to a history entry:

        /home/phil/utils/Cdll$ cd 1
        # Go to history entry 1.
        /home/phil/perl/eg$
        # Current directory is now what was 1

    To go to a special entry:

        /home/phil/perl/eg$ cd -s1
        # Go to special entry 1
        /home/phil/umm/ummdev$
        # Current directory is S1

    To go to a directory called, for example, 1:

        /home/phil$ cd -g 1
        # -g ignores the special meaning of 1
        /home/phil/1$

    To put current directory on the special list as S1:
        cd -r1 .        #  OR
        cd -R1 .        #  These have the same effect if the directory is
                        #+ . (the current directory)

    To go to a directory and add it as a special
      The directory for -r<n> or -R<n> may be a number.
      For example:
            $ cd -r3 4  Go to history entry 4 and put it on special entry 3
            $ cd -R3 4  Put current dir on the special entry 3 and go to
                        history entry 4
            $ cd -s3    Go to special entry 3

        Note that commands R,r,S and s may be used without a number and
        refer to 0:
            $ cd -s     Go to special entry 0
            $ cd -S     Go to special entry 0 and make special entry 0
                        current dir
            $ cd -r 1   Go to history entry 1 and put it on special entry 0
            $ cd -r     Go to history entry 0 and put it on special entry 0

        Alternative suggested directories:

        If a directory is not found, then CD will suggest any
        possibilities. These are directories starting with the same letters
        and if any are found they are listed prefixed with -a<n>
        where <n> is a number. It's possible to go to the directory
        by entering cd -a<n> on the command line.

            Use cd -d or -D to change default cd action. cd -H will show
            current action.

            The history entries (0-n) are stored in the environment variables
            CD[0] - CD[n]
            Similarly the special directories S0 - 9 are in the environment
            variable CDS[0] - CDS[9]
            and may be accessed from the command line, for example:

                ls -l ${CDS[3]}
                cat ${CD[8]}/file.txt

            The default pathname for the -f and -u commands is ~
            The default filename for the -f and -u commands is cdfile

    Configuration
    =============

        The following environment variables can be set:

            CDL_PROMPTLEN  - Set to the length of prompt you require.
                Prompt string is set to the right characters of the current
                directory. If not set, then prompt is left unchanged. Note
                that this is the number of characters that the directory is
                shortened to, not the total characters in the prompt.

                CDL_PROMPT_PRE - Set to the string to prefix the prompt.
                    Default is:
                        non-root:  "\\[\\e[01;34m\\]"  (sets colour to blue).
                        root:      "\\[\\e[01;31m\\]"  (sets colour to red).

                CDL_PROMPT_POST    - Set to the string to suffix the prompt.
                    Default is:
                        non-root:  "\\[\\e[00m\\]$"
                                   (resets colour and displays $).
                        root:      "\\[\\e[00m\\]#"
                                   (resets colour and displays #).

            Note:
                CDL_PROMPT_PRE & _POST only t

            CDPath - Set the default path for the -f & -u options.
                     Default is home directory
            CDFile - Set the default filename for the -f & -u options.
                     Default is cdfile

        There are three variables defined in the file cdll which control the
        number of entries stored or displayed. They are in the section labeled
        'Initialisation here' towards the end of the file.

            cd_maxhistory       - The number of history entries stored.
                                  Default is 50.
            cd_maxspecial       - The number of special entries allowed.
                                  Default is 9.
            cd_histcount        - The number of history and special entries
                                  displayed. Default is 9.

        Note that cd_maxspecial should be >= cd_histcount to avoid displaying
        special entries that can't be set.

    Version: 1.2.1 Date: 24-MAY-2003

    DOCUMENTATION

Example A-34. A soundcard setup script

    #!/bin/bash
    # soundcard-on.sh

    #  Script author: Mkarcher
    #  http://www.thinkwiki.org/wiki  ...
    #  /Script_for_configuring_the_CS4239_sound_chip_in_PnP_mode
    #  ABS Guide author made minor changes and added comments.
    #  Couldn't contact script author to ask for permission to use, but ...
    #+ the script was released under the FDL,
    #+ so its use here should be both legal and ethical.

    #  Sound-via-pnp-script for Thinkpad 600E
    #+ and possibly other computers with onboard CS4239/CS4610
    #+ that do not work with the PCI driver
    #+ and are not recognized by the PnP code of snd-cs4236.
    #  Also for some 770-series Thinkpads, such as the 770x.
    #  Run as root user, of course.
    #
    #  These are old and very obsolete laptop computers,
    #+ but this particular script is very instructive,
    #+ as it shows how to set up and hack device files.

    #  Search for sound card pnp device:

    for dev in /sys/bus/pnp/devices/*
    do
      grep CSC0100 $dev/id > /dev/null && WSSDEV=$dev
      grep CSC0110 $dev/id > /dev/null && CTLDEV=$dev
    done
    # On 770x:
    # WSSDEV = /sys/bus/pnp/devices/00:07
    # CTLDEV = /sys/bus/pnp/devices/00:06
    # These are symbolic links to /sys/devices/pnp0/ ...

    #  Activate devices:
    #  Thinkpad boots with devices disabled unless "fast boot" is turned off
    #+ (in BIOS).

    echo activate > $WSSDEV/resources
    echo activate > $CTLDEV/resources

    # Parse resource settings.

    { read # Discard "state = active" (see below).
      read bla port1
      read bla port2
      read bla port3
      read bla irq
      read bla dma1
      read bla dma2
     # The "bla's" are labels in the first field: "io," "state," etc.
     # These are discarded.

     #  Hack: with PnPBIOS: ports are: port1: WSS, port2:
     #+ OPL, port3: sb (unneeded)
     #       with ACPI-PnP:ports are: port1: OPL, port2: sb, port3: WSS
     #  (ACPI bios seems to be wrong here, the PnP-card-code in snd-cs4236.c
     #+  uses the PnPBIOS port order)
     #  Detect port order using the fixed OPL port as reference.
      if [ ${port2%%-*} = 0x388 ]
     #            ^^^^  Strip out everything following hyphen in port address.
     #                  So, if port1 is 0x530-0x537
     #+                 we're left with 0x530 -- the start address of the port.
     then
       # PnPBIOS: usual order
       port=${port1%%-*}
       oplport=${port2%%-*}
     else
       # ACPI: mixed-up order
       port=${port3%%-*}
       oplport=${port1%%-*}
     fi
     } < $WSSDEV/resources
    # To see what's going on here:
    # ---------------------------
    #   cat /sys/devices/pnp0/00:07/resources
    #
    #   state = active
    #   io 0x530-0x537
    #   io 0x388-0x38b
    #   io 0x220-0x233
    #   irq 5
    #   dma 1
    #   dma 0
    #   ^^^   "bla" labels in first field (discarded).

    { read # Discard first line, as above.
      read bla port1
      cport=${port1%%-*}
      #            ^^^^
      # Just want _start_ address of port.
    } < $CTLDEV/resources

    # Load the module:

    modprobe --ignore-install snd-cs4236 port=$port cport=$cport\
    fm_port=$oplport irq=$irq dma1=$dma1 dma2=$dma2 isapnp=0 index=0
    # See the modprobe manpage.

    exit $?

Example A-35. Locating split paragraphs in a text file

    #!/bin/bash
    # find-splitpara.sh
    #  Finds split paragraphs in a text file,
    #+ and tags the line numbers.

    ARGCOUNT=1       # Expect one arg.
    E_WRONGARGS=65

    file="$1"        # Target filename.
    lineno=1         # Line number. Start at 1.
    Flag=0           # Blank line flag.

    if [ $# -ne "$ARGCOUNT" ]
    then
      echo "Usage: `basename $0` FILENAME"
      exit $E_WRONGARGS
    fi

    file_read ()     # Scan file for pattern, then print line.
    {
    while read line
    do

      if [[ "$line" =~ ^[a-z] && $Flag -eq 1 ]]
         then  # Line begins with lc character, following blank line.
         echo -n "$lineno::   "
         echo "$line"
      fi

      if [[ "$line" =~ "^$" ]]
         then     #  If blank line,
         Flag=1   #+ set flag.
      else
         Flag=0
      fi

      ((lineno++))

    done
    } < $file  # Redirect file into function's stdin.

    file_read

    exit $?

    # ----------------------------------------------------------------
    This is line one of an example paragraph, bla, bla, bla.
    This is line two, and line three should follow on next line, but

    there is a blank line separating the two parts of the paragraph.
    # ----------------------------------------------------------------

    Running this script on a file containing the above paragraph
    yields:

    4::   there is a blank line separating the two parts of the paragraph.

    There will be additional output for all the other split paragraphs
    in the target file.

Example A-36. Insertion sort

    #!/bin/bash
    # insertion-sort.bash: Insertion sort implementation in Bash
    #                      Heavy use of Bash array features:
    #+                     (string) slicing, merging, etc
    # URL: http://www.lugmen.org.ar/~jjo/jjotip/insertion-sort.bash.d
    #+          /insertion-sort.bash.sh
    #
    # Author: JuanJo Ciarlante <jjo@irrigacion.gov.ar>
    # Lightly reformatted by ABS Guide author.
    # License: GPLv2
    # Used in ABS Guide with author's permission (thanks!).
    #
    # Test with:   ./insertion-sort.bash -t
    # Or:          bash insertion-sort.bash -t
    # The following *doesn't* work:
    #              sh insertion-sort.bash -t
    #  Why not? Hint: which Bash-specific features are disabled
    #+ when running a script by 'sh script.sh'?
    #
    : ${DEBUG:=0}  # Debug, override with:  DEBUG=1 ./scriptname . . .
    # Parameter substitution -- set DEBUG to 0 if not previously set.

    # Global array: "list"
    typeset -a list
    # Load whitespace-separated numbers from stdin.
    if [ "$1" = "-t" ]; then
    DEBUG=1
            read -a list < <( od -Ad -w24 -t u2 /dev/urandom ) # Random list.
    #                    ^ ^  process substition
    else
            read -a list
    fi
    numelem=${#list[*]}

    #  Shows the list, marking the element whose index is $1
    #+ by surrounding it with the two chars passed as $2.
    #  Whole line prefixed with $3.
    showlist()
      {
      echo "$3"${list[@]:0:$1} ${2:0:1}${list[$1]}${2:1:1} ${list[@]:$1+1};
      }

    # Loop _pivot_ -- from second element to end of list.
    for(( i=1; i<numelem; i++ )) do
            ((DEBUG))&&showlist i "[]" " "
            # From current _pivot_, back to first element.
            for(( j=i; j; j-- )) do
                    # Search for the 1st elem. less than current "pivot" . . .
                    [[ "${list[j-1]}" -le "${list[i]}" ]] && break
            done
    	(( i==j )) && continue ## No insertion was needed for this element.
    	# . . . Move list[i] (pivot) to the left of list[j]:
            list=(${list[@]:0:j} ${list[i]} ${list[j]}\
    	#         {0,j-1}        {i}       {j}
                  ${list[@]:j+1:i-(j+1)} ${list[@]:i+1})
    	#         {j+1,i-1}              {i+1,last}
    	((DEBUG))&&showlist j "<>" "*"
    done

    echo
    echo  "------"
    echo $'Result:\n'${list[@]}

    exit $?

Example A-37. Standard Deviation

    #!/bin/bash
    # sd.sh: Standard Deviation

    #  The Standard Deviation indicates how consistent a set of data is.
    #  It shows to what extent the individual data points deviate from the
    #+ arithmetic mean, i.e., how much they "bounce around" (or cluster).
    #  It is essentially the average deviation-distance of the
    #+ data points from the mean.

    # =========================================================== #
    #    To calculate the Standard Deviation:
    #
    # 1  Find the arithmetic mean (average) of all the data points.
    # 2  Subtract each data point from the arithmetic mean,
    #    and square that difference.
    # 3  Add all of the individual difference-squares in # 2.
    # 4  Divide the sum in # 3 by the number of data points.
    #    This is known as the "variance."
    # 5  The square root of # 4 gives the Standard Deviation.
    # =========================================================== #

    count=0         # Number of data points; global.
    SC=9            # Scale to be used by bc. Nine decimal places.
    E_DATAFILE=90   # Data file error.

    # ----------------- Set data file ---------------------
    if [ ! -z "$1" ]  # Specify filename as cmd-line arg?
    then
      datafile="$1" #  ASCII text file,
    else            #+ one (numerical) data point per line!
      datafile=sample.dat
    fi              #  See example data file, below.

    if [ ! -e "$datafile" ]
    then
      echo "\""$datafile"\" does not exist!"
      exit $E_DATAFILE
    fi
    # -----------------------------------------------------

    arith_mean ()
    {
      local rt=0         # Running total.
      local am=0         # Arithmetic mean.
      local ct=0         # Number of data points.

      while read value   # Read one data point at a time.
      do
        rt=$(echo "scale=$SC; $rt + $value" | bc)
        (( ct++ ))
      done

      am=$(echo "scale=$SC; $rt / $ct" | bc)

      echo $am; return $ct   # This function "returns" TWO values!
      #  Caution: This little trick will not work if $ct > 255!
      #  To handle a larger number of data points,
      #+ simply comment out the "return $ct" above.
    } <"$datafile"   # Feed in data file.

    sd ()
    {
      mean1=$1  # Arithmetic mean (passed to function).
      n=$2      # How many data points.
      sum2=0    # Sum of squared differences ("variance").
      avg2=0    # Average of $sum2.
      sdev=0    # Standard Deviation.

      while read value   # Read one line at a time.
      do
        diff=$(echo "scale=$SC; $mean1 - $value" | bc)
        # Difference between arith. mean and data point.
        dif2=$(echo "scale=$SC; $diff * $diff" | bc) # Squared.
        sum2=$(echo "scale=$SC; $sum2 + $dif2" | bc) # Sum of squares.
      done

        avg2=$(echo "scale=$SC; $sum2 / $n" | bc)  # Avg. of sum of squares.
        sdev=$(echo "scale=$SC; sqrt($avg2)" | bc) # Square root =
        echo $sdev                                 # Standard Deviation.

    } <"$datafile"   # Rewinds data file.

    # ======================================================= #
    mean=$(arith_mean); count=$?   # Two returns from function!
    std_dev=$(sd $mean $count)

    echo
    echo "Number of data points in \""$datafile"\" = $count"
    echo "Arithmetic mean (average) = $mean"
    echo "Standard Deviation = $std_dev"
    echo
    # ======================================================= #

    exit

    #  This script could stand some drastic streamlining,
    #+ but not at the cost of reduced legibility, please.

    # ++++++++++++++++++++++++++++++++++++++++ #
    # A sample data file (sample1.dat):

    # 18.35
    # 19.0
    # 18.88
    # 18.91
    # 18.64

    # $ sh sd.sh sample1.dat

    # Number of data points in "sample1.dat" = 5
    # Arithmetic mean (average) = 18.756000000
    # Standard Deviation = .235338054
    # ++++++++++++++++++++++++++++++++++++++++ #

Example A-38. A pad file generator for shareware authors

    #!/bin/bash
    # pad.sh

    #######################################################
    #               PAD (xml) file creator
    #+ Written by Mendel Cooper <thegrendel.abs@gmail.com>.
    #+ Released to the Public Domain.
    #
    #  Generates a "PAD" descriptor file for shareware
    #+ packages, according to the specifications
    #+ of the ASP.
    #  http://www.asp-shareware.org/pad
    #######################################################

    # Accepts (optional) save filename as a command-line argument.
    if [ -n "$1" ]
    then
      savefile=$1
    else
      savefile=save_file.xml               # Default save_file name.
    fi

    # ===== PAD file headers =====
    HDR1="<?xml version=\"1.0\" encoding=\"Windows-1252\" ?>"
    HDR2="<XML_DIZ_INFO>"
    HDR3="<MASTER_PAD_VERSION_INFO>"
    HDR4="\t<MASTER_PAD_VERSION>1.15</MASTER_PAD_VERSION>"
    HDR5="\t<MASTER_PAD_INFO>Portable Application Description, or PAD
    for short, is a data set that is used by shareware authors to
    disseminate information to anyone interested in their software products.
    To find out more go to http://www.asp-shareware.org/pad</MASTER_PAD_INFO>"
    HDR6="</MASTER_PAD_VERSION_INFO>"
    # ============================

    fill_in ()
    {
      if [ -z "$2" ]
      then
        echo -n "$1? "     # Get user input.
      else
        echo -n "$1 $2? "  # Additional query?
      fi

      read var             # May paste to fill in field.
                           # This shows how flexible "read" can be.

      if [ -z "$var" ]
      then
        echo -e "\t\t<$1 />" >>$savefile    # Indent with 2 tabs.
        return
      else
        echo -e "\t\t<$1>$var</$1>" >>$savefile
        return ${#var}     # Return length of input string.
      fi
    }

    check_field_length ()  # Check length of program description fields.
    {
      # $1 = maximum field length
      # $2 = actual field length
      if [ "$2" -gt "$1" ]
      then
        echo "Warning: Maximum field length of $1 characters exceeded!"
      fi
    }

    clear                  # Clear screen.
    echo "PAD File Creator"
    echo "--- ---- -------"
    echo

    # Write File Headers to file.
    echo $HDR1 >$savefile
    echo $HDR2 >>$savefile
    echo $HDR3 >>$savefile
    echo -e $HDR4 >>$savefile
    echo -e $HDR5 >>$savefile
    echo $HDR6 >>$savefile

    # Company_Info
    echo "COMPANY INFO"
    CO_HDR="Company_Info"
    echo "<$CO_HDR>" >>$savefile

    fill_in Company_Name
    fill_in Address_1
    fill_in Address_2
    fill_in City_Town
    fill_in State_Province
    fill_in Zip_Postal_Code
    fill_in Country

    # If applicable:
    # fill_in ASP_Member "[Y/N]"
    # fill_in ASP_Member_Number
    # fill_in ESC_Member "[Y/N]"

    fill_in Company_WebSite_URL

    clear   # Clear screen between sections.

       # Contact_Info
    echo "CONTACT INFO"
    CONTACT_HDR="Contact_Info"
    echo "<$CONTACT_HDR>" >>$savefile
    fill_in Author_First_Name
    fill_in Author_Last_Name
    fill_in Author_Email
    fill_in Contact_First_Name
    fill_in Contact_Last_Name
    fill_in Contact_Email
    echo -e "\t</$CONTACT_HDR>" >>$savefile
       # END Contact_Info

    clear

       # Support_Info
    echo "SUPPORT INFO"
    SUPPORT_HDR="Support_Info"
    echo "<$SUPPORT_HDR>" >>$savefile
    fill_in Sales_Email
    fill_in Support_Email
    fill_in General_Email
    fill_in Sales_Phone
    fill_in Support_Phone
    fill_in General_Phone
    fill_in Fax_Phone
    echo -e "\t</$SUPPORT_HDR>" >>$savefile
       # END Support_Info

    echo "</$CO_HDR>" >>$savefile
    # END Company_Info

    clear

    # Program_Info
    echo "PROGRAM INFO"
    PROGRAM_HDR="Program_Info"
    echo "<$PROGRAM_HDR>" >>$savefile
    fill_in Program_Name
    fill_in Program_Version
    fill_in Program_Release_Month
    fill_in Program_Release_Day
    fill_in Program_Release_Year
    fill_in Program_Cost_Dollars
    fill_in Program_Cost_Other
    fill_in Program_Type "[Shareware/Freeware/GPL]"
    fill_in Program_Release_Status "[Beta, Major Upgrade, etc.]"
    fill_in Program_Install_Support
    fill_in Program_OS_Support "[Win9x/Win2k/Linux/etc.]"
    fill_in Program_Language "[English/Spanish/etc.]"

    echo; echo

      # File_Info
    echo "FILE INFO"
    FILEINFO_HDR="File_Info"
    echo "<$FILEINFO_HDR>" >>$savefile
    fill_in Filename_Versioned
    fill_in Filename_Previous
    fill_in Filename_Generic
    fill_in Filename_Long
    fill_in File_Size_Bytes
    fill_in File_Size_K
    fill_in File_Size_MB
    echo -e "\t</$FILEINFO_HDR>" >>$savefile
      # END File_Info

    clear

      # Expire_Info
    echo "EXPIRE INFO"
    EXPIRE_HDR="Expire_Info"
    echo "<$EXPIRE_HDR>" >>$savefile
    fill_in Has_Expire_Info "Y/N"
    fill_in Expire_Count
    fill_in Expire_Based_On
    fill_in Expire_Other_Info
    fill_in Expire_Month
    fill_in Expire_Day
    fill_in Expire_Year
    echo -e "\t</$EXPIRE_HDR>" >>$savefile
      # END Expire_Info

    clear

      # More Program_Info
    echo "ADDITIONAL PROGRAM INFO"
    fill_in Program_Change_Info
    fill_in Program_Specific_Category
    fill_in Program_Categories
    fill_in Includes_JAVA_VM "[Y/N]"
    fill_in Includes_VB_Runtime "[Y/N]"
    fill_in Includes_DirectX "[Y/N]"
      # END More Program_Info

    echo "</$PROGRAM_HDR>" >>$savefile
    # END Program_Info

    clear

    # Program Description
    echo "PROGRAM DESCRIPTIONS"
    PROGDESC_HDR="Program_Descriptions"
    echo "<$PROGDESC_HDR>" >>$savefile

    LANG="English"
    echo "<$LANG>" >>$savefile

    fill_in Keywords "[comma + space separated]"
    echo
    echo "45, 80, 250, 450, 2000 word program descriptions"
    echo "(may cut and paste into field)"
    #  It would be highly appropriate to compose the following
    #+ "Char_Desc" fields with a text editor,
    #+ then cut-and-paste the text into the answer fields.
    echo
    echo "              |---------------45 characters---------------|"
    fill_in Char_Desc_45
    check_field_length 45 "$?"
    echo
    fill_in Char_Desc_80
    check_field_length 80 "$?"

    fill_in Char_Desc_250
    check_field_length 250 "$?"

    fill_in Char_Desc_450
    fill_in Char_Desc_2000

    echo "</$LANG>" >>$savefile
    echo "</$PROGDESC_HDR>" >>$savefile
    # END Program Description

    clear
    echo "Done."; echo; echo
    echo "Save file is:  \""$savefile"\""

    exit 0

Example A-39. A man page editor

    #!/bin/bash
    # maned.sh
    # A rudimentary man page editor

    # Version: 0.1 (Alpha, probably buggy)
    # Author: Mendel Cooper <thegrendel.abs@gmail.com>
    # Reldate: 16 June 2008
    # License: GPL3

    savefile=      # Global, used in multiple functions.
    E_NOINPUT=90   # User input missing (error). May or may not be critical.

    # =========== Markup Tags ============ #
    TopHeader=".TH"
    NameHeader=".SH NAME"
    SyntaxHeader=".SH SYNTAX"
    SynopsisHeader=".SH SYNOPSIS"
    InstallationHeader=".SH INSTALLATION"
    DescHeader=".SH DESCRIPTION"
    OptHeader=".SH OPTIONS"
    FilesHeader=".SH FILES"
    EnvHeader=".SH ENVIRONMENT"
    AuthHeader=".SH AUTHOR"
    BugsHeader=".SH BUGS"
    SeeAlsoHeader=".SH SEE ALSO"
    BOLD=".B"
    # Add more tags, as needed.
    # See groff docs for markup meanings.
    # ==================================== #

    start ()
    {
    clear                  # Clear screen.
    echo "ManEd"
    echo "-----"
    echo
    echo "Simple man page creator"
    echo "Author: Mendel Cooper"
    echo; echo; echo
    }

    progname ()
    {
      echo -n "Program name? "
      read name

      echo -n "Manpage section? [Hit RETURN for default (\"1\") ]  "
      read section
      if [ -z "$section" ]
      then
        section=1   # Most man pages are in section 1.
      fi

      if [ -n "$name" ]
      then
        savefile=""$name"."$section""       #  Filename suffix = section.
        echo -n "$1 " >>$savefile
        name1=$(echo "$name" | tr a-z A-Z)  #  Change to uppercase,
                                            #+ per man page convention.
        echo -n "$name1" >>$savefile
      else
        echo "Error! No input."             # Mandatory input.
        exit $E_NOINPUT                     # Critical!
        #  Exercise: The script-abort if no filename input is a bit clumsy.
        #            Rewrite this section so a default filename is used
        #+           if no input.
      fi

      echo -n "  \"$section\"">>$savefile   # Append, always append.

      echo -n "Version? "
      read ver
      echo -n " \"Version $ver \"">>$savefile
      echo >>$savefile

      echo -n "Short description [0 - 5 words]? "
      read sdesc
      echo "$NameHeader">>$savefile
      echo ""$BOLD" "$name"">>$savefile
      echo "\- "$sdesc"">>$savefile

    }

    fill_in ()
    { # This function more or less copied from "pad.sh" script.
      echo -n "$2? "       # Get user input.
      read var             # May paste (a single line only!) to fill in field.

      if [ -n "$var" ]
      then
        echo "$1 " >>$savefile
        echo -n "$var" >>$savefile
      else                 # Don't append empty field to file.
        return $E_NOINPUT  # Not critical here.
      fi

      echo >>$savefile

    }

    end ()
    {
    clear
    echo -n "Would you like to view the saved man page (y/n)? "
    read ans
    if [ "$ans" = "n" -o "$ans" = "N" ]; then exit; fi
    exec less "$savefile"  #  Exit script and hand off control to "less" ...
                           #+ ... which formats for viewing man page source.
    }

    # ---------------------------------------- #
    start
    progname "$TopHeader"
    fill_in "$SynopsisHeader" "Synopsis"
    fill_in "$DescHeader" "Long description"
    # May paste in *single line* of text.
    fill_in "$OptHeader" "Options"
    fill_in "$FilesHeader" "Files"
    fill_in "$AuthHeader" "Author"
    fill_in "$BugsHeader" "Bugs"
    fill_in "$SeeAlsoHeader" "See also"
    # fill_in "$OtherHeader" ... as necessary.
    end    # ... exit not needed.
    # ---------------------------------------- #

    #  Note that the generated man page will usually
    #+ require manual fine-tuning with a text editor.
    #  However, it's a distinct improvement upon
    #+ writing man source from scratch
    #+ or even editing a blank man page template.

    #  The main deficiency of the script is that it permits
    #+ pasting only a single text line into the input fields.
    #  This may be a long, cobbled-together line, which groff
    #  will automatically wrap and hyphenate.
    #  However, if you want multiple (newline-separated) paragraphs,
    #+ these must be inserted by manual text editing on the
    #+ script-generated man page.
    #  Exercise (difficult): Fix this!

    #  This script is not nearly as elaborate as the
    #+ full-featured "manedit" package
    #+ http://freshmeat.net/projects/manedit/
    #+ but it's much easier to use.

Example A-40. Petals Around the Rose

    #!/bin/bash -i
    # petals.sh

    #########################################################################
    # Petals Around the Rose                                                #
    #                                                                       #
    # Version 0.1 Created by Serghey Rodin                                  #
    # Version 0.2 Modded by ABS Guide Author                                #
    #                                                                       #
    # License: GPL3                                                         #
    # Used in ABS Guide with permission.                                    #
    # ##################################################################### #

    hits=0      # Correct guesses.
    WIN=6       # Mastered the game.
    ALMOST=5    # One short of mastery.
    EXIT=exit   # Give up early?

    RANDOM=$$   # Seeds the random number generator from PID of script.

    # Bones (ASCII graphics for dice)
    bone1[1]="|         |"
    bone1[2]="|       o |"
    bone1[3]="|       o |"
    bone1[4]="| o     o |"
    bone1[5]="| o     o |"
    bone1[6]="| o     o |"
    bone2[1]="|    o    |"
    bone2[2]="|         |"
    bone2[3]="|    o    |"
    bone2[4]="|         |"
    bone2[5]="|    o    |"
    bone2[6]="| o     o |"
    bone3[1]="|         |"
    bone3[2]="| o       |"
    bone3[3]="| o       |"
    bone3[4]="| o     o |"
    bone3[5]="| o     o |"
    bone3[6]="| o     o |"
    bone="+---------+"

    # Functions

    instructions () {

      clear
      echo -n "Do you need instructions? (y/n) "; read ans
      if [ "$ans" = "y" -o "$ans" = "Y" ]; then
        clear
        echo -e '\E[34;47m'  # Blue type.

    #  "cat document"
        cat <<INSTRUCTIONSZZZ
    The name of the game is Petals Around the Rose,
    and that name is significant.
    Five dice will roll and you must guess the "answer" for each roll.
    It will be zero or an even number.
    After your guess, you will be told the answer for the roll, but . . .
    that's ALL the information you will get.

    Six consecutive correct guesses admits you to the
    Fellowship of the Rose.
    INSTRUCTIONSZZZ

        echo -e "\033[0m"    # Turn off blue.
        else clear
      fi

    }

    fortune ()
    {
      RANGE=7
      FLOOR=0
      number=0
      while [ "$number" -le $FLOOR ]
      do
        number=$RANDOM
        let "number %= $RANGE"   # 1 - 6.
      done

      return $number
    }

    throw () { # Calculate each individual die.
      fortune; B1=$?
      fortune; B2=$?
      fortune; B3=$?
      fortune; B4=$?
      fortune; B5=$?

      calc () { # Function embedded within a function!
        case "$1" in
           3   ) rose=2;;
           5   ) rose=4;;
           *   ) rose=0;;
        esac    # Simplified algorithm.
                # Doesn't really get to the heart of the matter.
        return $rose
      }

      answer=0
      calc "$B1"; answer=$(expr $answer + $(echo $?))
      calc "$B2"; answer=$(expr $answer + $(echo $?))
      calc "$B3"; answer=$(expr $answer + $(echo $?))
      calc "$B4"; answer=$(expr $answer + $(echo $?))
      calc "$B5"; answer=$(expr $answer + $(echo $?))
    }

    game ()
    { # Generate graphic display of dice throw.
      throw
        echo -e "\033[1m"    # Bold.
      echo -e "\n"
      echo -e "$bone\t$bone\t$bone\t$bone\t$bone"
      echo -e \
     "${bone1[$B1]}\t${bone1[$B2]}\t${bone1[$B3]}\t${bone1[$B4]}\t${bone1[$B5]}"
      echo -e \
     "${bone2[$B1]}\t${bone2[$B2]}\t${bone2[$B3]}\t${bone2[$B4]}\t${bone2[$B5]}"
      echo -e \
     "${bone3[$B1]}\t${bone3[$B2]}\t${bone3[$B3]}\t${bone3[$B4]}\t${bone3[$B5]}"
      echo -e "$bone\t$bone\t$bone\t$bone\t$bone"
      echo -e "\n\n\t\t"
        echo -e "\033[0m"    # Turn off bold.
      echo -n "There are how many petals around the rose? "
    }

    # ============================================================== #

    instructions

    while [ "$petal" != "$EXIT" ]    # Main loop.
    do
      game
      read petal
      echo "$petal" | grep [0-9] >/dev/null  # Filter response for digit.
                                             # Otherwise just roll dice again.
      if [ "$?" -eq 0 ]   # If-loop #1.
      then
        if [ "$petal" == "$answer" ]; then    # If-loop #2.
        	echo -e "\nCorrect. There are $petal petals around the rose.\n"
            (( hits++ ))

            if [ "$hits" -eq "$WIN" ]; then   # If-loop #3.
              echo -e '\E[31;47m'  # Red type.
              echo -e "\033[1m"    # Bold.
              echo "You have unraveled the mystery of the Rose Petals!"
              echo "Welcome to the Fellowship of the Rose!!!"
              echo "(You are herewith sworn to secrecy.)"; echo
              echo -e "\033[0m"    # Turn off red & bold.
              break                # Exit!
            else echo "You have $hits correct so far."; echo

            if [ "$hits" -eq "$ALMOST" ]; then
              echo "Just one more gets you to the heart of the mystery!"; echo
            fi

          fi                                  # Close if-loop #3.

        else
          echo -e "\nWrong. There are $answer petals around the rose.\n"
          hits=0   # Reset number of correct guesses.
        fi                                    # Close if-loop #2.

        echo -n "Hit ENTER for the next roll, or type \"exit\" to end. "
        read
        if [ "$REPLY" = "$EXIT" ]; then exit
        fi

      fi                  # Close if-loop #1.

      clear
    done                  # End of main (while) loop.

    ###

    exit $?

    # Resources:
    # ---------
    # 1) http://en.wikipedia.org/wiki/Petals_Around_the_Rose
    #    (Wikipedia entry.)
    # 2) http://www.borrett.id.au/computing/petals-bg.htm
    #    (How Bill Gates coped with the Petals Around the Rose challenge.)

Example A-41. Quacky: a Perquackey-type word game

    #!/bin/bash
    # qky.sh

    ##############################################################
    # QUACKEY: a somewhat simplified version of Perquackey [TM]. #
    #                                                            #
    # Author: Mendel Cooper  <thegrendel.abs@gmail.com>          #
    # version 0.1.02      03 May, 2008                           #
    # License: GPL3                                              #
    ##############################################################

    WLIST=/usr/share/dict/word.lst
    #                     ^^^^^^^^  Word list file found here.
    #  ASCII word list, one word per line, UNIX format.
    #  A suggested list is the script author's "yawl" word list package.
    #  http://bash.deta.in/yawl-0.3.2.tar.gz
    #    or
    #  http://ibiblio.org/pub/Linux/libs/yawl-0.3.2.tar.gz

    NONCONS=0     # Word not constructable from letter set.
    CONS=1        # Constructable.
    SUCCESS=0
    NG=1
    FAILURE=''
    NULL=0        # Zero out value of letter (if found).
    MINWLEN=3     # Minimum word length.
    MAXCAT=5      # Maximum number of words in a given category.
    PENALTY=200   # General-purpose penalty for unacceptable words.
    total=
    E_DUP=70      # Duplicate word error.

    TIMEOUT=10    # Time for word input.

    NVLET=10      # 10 letters for non-vulnerable.
    VULET=13      # 13 letters for vulnerable (not yet implemented!).

    declare -a Words
    declare -a Status
    declare -a Score=( 0 0 0 0 0 0 0 0 0 0 0 )

    letters=( a n s r t m l k p r b c i d s i d z e w u e t f
    e y e r e f e g t g h h i t r s c i t i d i j a t a o l a
    m n a n o v n w o s e l n o s p a q e e r a b r s a o d s
    t g t i t l u e u v n e o x y m r k )
    #  Letter distribution table shamelessly borrowed from "Wordy" game,
    #+ ca. 1992, written by a certain fine fellow named Mendel Cooper.

    declare -a LS

    numelements=${#letters[@]}
    randseed="$1"

    instructions ()
    {
      clear
      echo "Welcome to QUACKEY, the anagramming word construction game."; echo
      echo -n "Do you need instructions? (y/n) "; read ans

       if [ "$ans" = "y" -o "$ans" = "Y" ]; then
         clear
         echo -e '\E[31;47m'  # Red foreground. '\E[34;47m' for blue.
         cat <<INSTRUCTION1

    QUACKEY is a variant of Perquackey [TM].
    The rules are the same, but the scoring is simplified
    and plurals of previously played words are allowed.
    "Vulnerable" play is not yet implemented,
    but it is otherwise feature-complete.

    As the game begins, the player gets 10 letters.
    The object is to construct valid dictionary words
    of at least 3-letter length from the letterset.
    Each word-length category
    -- 3-letter, 4-letter, 5-letter, ... --
    fills up with the fifth word entered,
    and no further words in that category are accepted.

    The penalty for too-short (two-letter), duplicate, unconstructable,
    and invalid (not in dictionary) words is -200. The same penalty applies
    to attempts to enter a word in a filled-up category.

    INSTRUCTION1

      echo -n "Hit ENTER for next page of instructions. "; read az1

         cat <<INSTRUCTION2

    The scoring mostly corresponds to classic Perquackey:
    The first 3-letter word scores    60, plus   10 for each additional one.
    The first 4-letter word scores   120, plus   20 for each additional one.
    The first 5-letter word scores   200, plus   50 for each additional one.
    The first 6-letter word scores   300, plus  100 for each additional one.
    The first 7-letter word scores   500, plus  150 for each additional one.
    The first 8-letter word scores   750, plus  250 for each additional one.
    The first 9-letter word scores  1000, plus  500 for each additional one.
    The first 10-letter word scores 2000, plus 2000 for each additional one.

    Category completion bonuses are:
    3-letter words   100
    4-letter words   200
    5-letter words   400
    6-letter words   800
    7-letter words  2000
    8-letter words 10000
    This is a simplification of the absurdly baroque Perquackey bonus
    scoring system.

    INSTRUCTION2

      echo -n "Hit ENTER for final page of instructions. "; read az1

         cat <<INSTRUCTION3

    Hitting just ENTER for a word entry ends the game.

    Individual word entry is timed to a maximum of 10 seconds.
    *** Timing out on an entry ends the game. ***
    Aside from that, the game is untimed.

    --------------------------------------------------
    Game statistics are automatically saved to a file.
    --------------------------------------------------

    For competitive ("duplicate") play, a previous letterset
    may be duplicated by repeating the script's random seed,
    command-line parameter \$1.
    For example, "qky 7633" specifies the letterset
    c a d i f r h u s k ...
    INSTRUCTION3

      echo; echo -n "Hit ENTER to begin game. "; read az1

           echo -e "\033[0m"    # Turn off red.
         else clear
      fi

      clear

    }

    seed_random ()
    {                         #  Seed random number generator.
      if [ -n "$randseed" ]   #  Can specify random seed.
      then                    #+ for play in competitive mode.
    #   RANDOM="$randseed"
        echo "RANDOM seed set to "$randseed""
      else
        randseed="$$"         # Or get random seed from process ID.
        echo "RANDOM seed not specified, set to Process ID of script ($$)."
      fi

      RANDOM="$randseed"

      echo
    }

    get_letset ()
    {
      element=0
      echo -n "Letterset:"

      for lset in $(seq $NVLET)
      do  # Pick random letters to fill out letterset.
        LS[element]="${letters[$((RANDOM%numelements))]}"
        ((element++))
      done

      echo
      echo "${LS[@]}"

    }

    add_word ()
    {
      wrd="$1"
      local idx=0

      Status[0]=""
      Status[3]=""
      Status[4]=""

      while [ "${Words[idx]}" != '' ]
      do
        if [ "${Words[idx]}" = "$wrd" ]
        then
          Status[3]="Duplicate-word-PENALTY"
          let "Score[0]= 0 - $PENALTY"
          let "Score[1]-=$PENALTY"
          return $E_DUP
        fi

        ((idx++))
      done

      Words[idx]="$wrd"
      get_score

    }

    get_score()
    {
      local wlen=0
      local score=0
      local bonus=0
      local first_word=0
      local add_word=0
      local numwords=0

      wlen=${#wrd}
      numwords=${Score[wlen]}
      Score[2]=0
      Status[4]=""   # Initialize "bonus" to 0.

      case "$wlen" in
        3) first_word=60
           add_word=10;;
        4) first_word=120
           add_word=20;;
        5) first_word=200
           add_word=50;;
        6) first_word=300
           add_word=100;;
        7) first_word=500
           add_word=150;;
        8) first_word=750
           add_word=250;;
        9) first_word=1000
           add_word=500;;
       10) first_word=2000
           add_word=2000;;   # This category modified from original rules!
          esac

      ((Score[wlen]++))
      if [ ${Score[wlen]} -eq $MAXCAT ]
      then   # Category completion bonus scoring simplified!
        case $wlen in
          3 ) bonus=100;;
          4 ) bonus=200;;
          5 ) bonus=400;;
          6 ) bonus=800;;
          7 ) bonus=2000;;
          8 ) bonus=10000;;
        esac  # Needn't worry about 9's and 10's.
        Status[4]="Category-$wlen-completion***BONUS***"
        Score[2]=$bonus
      else
        Status[4]=""   # Erase it.
      fi

        let "score =  $first_word +   $add_word * $numwords"
        if [ "$numwords" -eq 0 ]
        then
          Score[0]=$score
        else
          Score[0]=$add_word
        fi   #  All this to distinguish last-word score
             #+ from total running score.
      let "Score[1] += ${Score[0]}"
      let "Score[1] += ${Score[2]}"

    }

    get_word ()
    {
      local wrd=''
      read -t $TIMEOUT wrd   # Timed read.
      echo $wrd
    }

    is_constructable ()
    { # This is the most complex and difficult-to-write function.
      local -a local_LS=( "${LS[@]}" )  # Local copy of letter set.
      local is_found=0
      local idx=0
      local pos
      local strlen
      local local_word=( "$1" )
      strlen=${#local_word}

      while [ "$idx" -lt "$strlen" ]
      do
        is_found=$(expr index "${local_LS[*]}" "${local_word:idx:1}")
        if [ "$is_found" -eq "$NONCONS" ] # Not constructable!
        then
          echo "$FAILURE"; return
        else
          ((pos = ($is_found - 1) / 2))   # Compensate for spaces betw. letters!
          local_LS[pos]=$NULL             # Zero out used letters.
          ((idx++))                       # Bump index.
        fi
      done

      echo "$SUCCESS"
      return
    }

    is_valid ()
    { # Surprisingly easy to check if word in dictionary ...
      fgrep -qw "$1" "$WLIST"   # ... courtesy of 'grep' ...
      echo $?
    }

    check_word ()
    {
      if [ -z "$1" ]
      then
        return
      fi

      Status[1]=""
      Status[2]=""
      Status[3]=""
      Status[4]=""

      iscons=$(is_constructable "$1")
      if [ "$iscons" ]
      then
        Status[1]="constructable"
        v=$(is_valid "$1")
        if [ "$v" -eq "$SUCCESS" ]
        then
          Status[2]="valid"
          strlen=${#1}

          if [ ${Score[strlen]} -eq "$MAXCAT" ]   # Category full!
          then
            Status[3]="Category-$strlen-overflow-PENALTY"
            return $NG
          fi

          case "$strlen" in
            1 | 2 )
            Status[3]="Two-letter-word-PENALTY"
            return $NG;;
            * )
    	Status[3]=""
    	return $SUCCESS;;
          esac
        else
          Status[3]="Not-valid-PENALTY"
          return $NG
        fi
      else
        Status[3]="Not-constructable-PENALTY"
          return $NG
      fi

      ### FIXME: Streamline the above code block.

    }

    display_words ()
    {
      local idx=0
      local wlen0

      clear
      echo "Letterset:   ${LS[@]}"
      echo "Threes:    Fours:    Fives:     Sixes:    Sevens:    Eights:"
      echo "------------------------------------------------------------"

      while [ "${Words[idx]}" != '' ]
      do
       wlen0=${#Words[idx]}
       case "$wlen0" in
         3) ;;
         4) echo -n "           " ;;
         5) echo -n "                     " ;;
         6) echo -n "                                " ;;
         7) echo -n "                                          " ;;
         8) echo -n "                                                     " ;;
       esac
       echo "${Words[idx]}"
       ((idx++))
      done

      ### FIXME: The word display is pretty crude.
    }

    play ()
    {
      word="Start game"   # Dummy word, to start ...

      while [ "$word" ]   #  If player just hits return (null word),
      do                  #+ then game ends.
        echo "$word: "${Status[@]}""
        echo -n "Last score: [${Score[0]}]   TOTAL score: [${Score[1]}]:     Next word: "
        total=${Score[1]}
        word=$(get_word)
        check_word "$word"

        if [ "$?" -eq "$SUCCESS" ]
        then
          add_word "$word"
        else
          let "Score[0]= 0 - $PENALTY"
          let "Score[1]-=$PENALTY"
        fi

      display_words
      done   # Exit game.

      ### FIXME: The play () function calls too many other functions.
      ### This verges on "spaghetti code" !!!
    }

    end_of_game ()
    { # Save and display stats.

      #######################Autosave##########################
      savefile=qky.save.$$
      #                 ^^ PID of script
      echo `date` >> $savefile
      echo "Letterset # $randseed  (random seed) ">> $savefile
      echo -n "Letterset: " >> $savefile
      echo "${LS[@]}" >> $savefile
      echo "---------" >> $savefile
      echo "Words constructed:" >> $savefile
      echo "${Words[@]}" >> $savefile
      echo >> $savefile
      echo "Score: $total" >> $savefile

      echo "Statistics for this round saved in \""$savefile"\""
      #########################################################

      echo "Score for this round: $total"
      echo "Words:  ${Words[@]}"
    }

    # ---------#
    instructions
    seed_random
    get_letset
    play
    end_of_game
    # ---------#

    exit $?

    # TODO:
    #
    # 1) Clean up code!
    # 2) Prettify the display_words () function (maybe with widgets?).
    # 3) Improve the time-out ... maybe change to untimed entry,
    #+   but with a time limit for the overall round.
    # 4) An on-screen countdown timer would be nice.
    # 5) Implement "vulnerable" mode of play for compatibility with classic
    #+   version of the game.
    # 6) Improve save-to-file capability (and maybe make it optional).
    # 7) Fix bugs!!!

    # For more info, reference:
    # http://bash.deta.in/qky.README.html

Example A-42. Nim

    #!/bin/bash
    # nim.sh: Game of Nim

    # Author: Mendel Cooper
    # Reldate: 15 July 2008
    # License: GPL3

    ROWS=5     # Five rows of pegs (or matchsticks).
    WON=91     # Exit codes to keep track of wins/losses.
    LOST=92    # Possibly useful if running in batch mode.
    QUIT=99
    peg_msg=   # Peg/Pegs?
    Rows=( 0 5 4 3 2 1 )   # Array holding play info.
    # ${Rows[0]} holds total number of pegs, updated after each turn.
    # Other array elements hold number of pegs in corresponding row.

    instructions ()
    {
      clear
      tput bold
      echo "Welcome to the game of Nim."; echo
      echo -n "Do you need instructions? (y/n) "; read ans

       if [ "$ans" = "y" -o "$ans" = "Y" ]; then
         clear
         echo -e '\E[33;41m'  # Yellow fg., over red bg.; bold.
         cat <<INSTRUCTIONS

    Nim is a game with roots in the distant past.
    This particular variant starts with five rows of pegs.

    1:    | | | | |
    2:     | | | |
    3:      | | |
    4:       | |
    5:        |

    The number at the left identifies the row.

    The human player moves first, and alternates turns with the bot.
    A turn consists of removing at least one peg from a single row.
    It is permissable to remove ALL the pegs from a row.
    For example, in row 2, above, the player can remove 1, 2, 3, or 4 pegs.
    The player who removes the last peg loses.

    The strategy consists of trying to be the one who removes
    the next-to-last peg(s), leaving the loser with the final peg.

    To exit the game early, hit ENTER during your turn.
    INSTRUCTIONS

    echo; echo -n "Hit ENTER to begin game. "; read azx

          echo -e "\033[0m"    # Restore display.
          else tput sgr0; clear
      fi

    clear

    }

    tally_up ()
    {
      let "Rows[0] = ${Rows[1]} + ${Rows[2]} + ${Rows[3]} + ${Rows[4]} + \
      ${Rows[5]}"    # Add up how many pegs remaining.
    }

    display ()
    {
      index=1   # Start with top row.
      echo

      while [ "$index" -le "$ROWS" ]
      do
        p=${Rows[index]}
        echo -n "$index:   "          # Show row number.

      # ------------------------------------------------
      # Two concurrent inner loops.

          indent=$index
          while [ "$indent" -gt 0 ]
          do
            echo -n " "               # Staggered rows.
            ((indent--))              # Spacing between pegs.
          done

        while [ "$p" -gt 0 ]
        do
          echo -n "| "
          ((p--))
        done
      # -----------------------------------------------

      echo
      ((index++))
      done

      tally_up

      rp=${Rows[0]}

      if [ "$rp" -eq 1 ]
      then
        peg_msg=peg
        final_msg="Game over."
      else             # Game not yet over . . .
        peg_msg=pegs
        final_msg=""   # . . . So "final message" is blank.
      fi

      echo "      $rp $peg_msg remaining."
      echo "      "$final_msg""

      echo
    }

    player_move ()
    {

      echo "Your move:"

      echo -n "Which row? "
      while read idx
      do                   # Validity check, etc.

        if [ -z "$idx" ]   # Hitting return quits.
        then
            echo "Premature exit."; echo
            tput sgr0      # Restore display.
            exit $QUIT
        fi

        if [ "$idx" -gt "$ROWS" -o "$idx" -lt 1 ]   # Bounds check.
        then
          echo "Invalid row number!"
          echo -n "Which row? "
        else
          break
        fi
        # TODO:
        # Add check for non-numeric input.
        # Also, script crashes on input outside of range of long double.
        # Fix this.

      done

      echo -n "Remove how many? "
      while read num
      do                   # Validity check.

      if [ -z "$num" ]
      then
        echo "Premature exit."; echo
        tput sgr0          # Restore display.
        exit $QUIT
      fi

        if [ "$num" -gt ${Rows[idx]} -o "$num" -lt 1 ]
        then
          echo "Cannot remove $num!"
          echo -n "Remove how many? "
        else
          break
        fi
      done
      # TODO:
      # Add check for non-numeric input.
      # Also, script crashes on input outside of range of long double.
      # Fix this.

      let "Rows[idx] -= $num"

      display
      tally_up

      if [ ${Rows[0]} -eq 1 ]
      then
       echo "      Human wins!"
       echo "      Congratulations!"
       tput sgr0   # Restore display.
       echo
       exit $WON
      fi

      if [ ${Rows[0]} -eq 0 ]
      then          # Snatching defeat from the jaws of victory . . .
        echo "      Fool!"
        echo "      You just removed the last peg!"
        echo "      Bot wins!"
        tput sgr0   # Restore display.
        echo
        exit $LOST
      fi
    }

    bot_move ()
    {

      row_b=0
      while [[ $row_b -eq 0 || ${Rows[row_b]} -eq 0 ]]
      do
        row_b=$RANDOM          # Choose random row.
        let "row_b %= $ROWS"
      done

      num_b=0
      r0=${Rows[row_b]}

      if [ "$r0" -eq 1 ]
      then
        num_b=1
      else
        let "num_b = $r0 - 1"
             #  Leave only a single peg in the row.
      fi     #  Not a very strong strategy,
             #+ but probably a bit better than totally random.

      let "Rows[row_b] -= $num_b"
      echo -n "Bot:  "
      echo "Removing from row $row_b ... "

      if [ "$num_b" -eq 1 ]
      then
        peg_msg=peg
      else
        peg_msg=pegs
      fi

      echo "      $num_b $peg_msg."

      display
      tally_up

      if [ ${Rows[0]} -eq 1 ]
      then
       echo "      Bot wins!"
       tput sgr0   # Restore display.
       exit $WON
      fi

    }

    # ================================================== #
    instructions     # If human player needs them . . .
    tput bold        # Bold characters for easier viewing.
    display          # Show game board.

    while [ true ]   # Main loop.
    do               # Alternate human and bot turns.
      player_move
      bot_move
    done
    # ================================================== #

    # Exercise:
    # --------
    # Improve the bot's strategy.
    # There is, in fact, a Nim strategy that can force a win.
    # See the Wikipedia article on Nim:  http://en.wikipedia.org/wiki/Nim
    # Recode the bot to use this strategy (rather difficult).

    #  Curiosities:
    #  -----------
    #  Nim played a prominent role in Alain Resnais' 1961 New Wave film,
    #+ Last Year at Marienbad.
    #
    #  In 1978, Leo Christopherson wrote an animated version of Nim,
    #+ Android Nim, for the TRS-80 Model I.

Example A-43. A command-line stopwatch

    #!/bin/sh
    # sw.sh
    # A command-line Stopwatch

    # Author: Pádraig Brady
    #    http://www.pixelbeat.org/scripts/sw
    #    (Minor reformatting by ABS Guide author.)
    #    Used in ABS Guide with script author's permission.
    # Notes:
    #    This script starts a few processes per lap, in addition to
    #    the shell loop processing, so the assumption is made that
    #    this takes an insignificant amount of time compared to
    #    the response time of humans (~.1s) (or the keyboard
    #    interrupt rate (~.05s)).
    #    '?' for splits must be entered twice if characters
    #    (erroneously) entered before it (on the same line).
    #    '?' since not generating a signal may be slightly delayed
    #    on heavily loaded systems.
    #    Lap timings on ubuntu may be slightly delayed due to:
    #    https://bugs.launchpad.net/bugs/62511
    # Changes:
    #    V1.0, 23 Aug 2005, Initial release
    #    V1.1, 26 Jul 2007, Allow both splits and laps from single invocation.
    #                       Only start timer after a key is pressed.
    #                       Indicate lap number
    #                       Cache programs at startup so there is less error
    #                       due to startup delays.
    #    V1.2, 01 Aug 2007, Work around `date` commands that don't have
    #                       nanoseconds.
    #                       Use stty to change interrupt keys to space for
    #                       laps etc.
    #                       Ignore other input as it causes problems.
    #    V1.3, 01 Aug 2007, Testing release.
    #    V1.4, 02 Aug 2007, Various tweaks to get working under ubuntu
    #                       and Mac OS X.
    #    V1.5, 27 Jun 2008, set LANG=C as got vague bug report about it.

    export LANG=C

    ulimit -c 0   # No coredumps from SIGQUIT.
    trap '' TSTP  # Ignore Ctrl-Z just in case.
    save_tty=`stty -g` && trap "stty $save_tty" EXIT  # Restore tty on exit.
    stty quit ' ' # Space for laps rather than Ctrl-\.
    stty eof  '?' # ? for splits rather than Ctrl-D.
    stty -echo    # Don't echo input.

    cache_progs() {
        stty > /dev/null
        date > /dev/null
        grep . < /dev/null
        (echo "import time" | python) 2> /dev/null
        bc < /dev/null
        sed '' < /dev/null
        printf '1' > /dev/null
        /usr/bin/time false 2> /dev/null
        cat < /dev/null
    }
    cache_progs   # To minimise startup delay.

    date +%s.%N | grep -qF 'N' && use_python=1 # If `date` lacks nanoseconds.
    now() {
        if [ "$use_python" ]; then
            echo "import time; print time.time()" 2>/dev/null | python
        else
            printf "%.2f" `date +%s.%N`
        fi
    }

    fmt_seconds() {
        seconds=$1
        mins=`echo $seconds/60 | bc`
        if [ "$mins" != "0" ]; then
            seconds=`echo "$seconds - ($mins*60)" | bc`
            echo "$mins:$seconds"
        else
            echo "$seconds"
        fi
    }

    total() {
        end=`now`
        total=`echo "$end - $start" | bc`
        fmt_seconds $total
    }

    stop() {
        [ "$lapped" ] && lap "$laptime" "display"
        total
        exit
    }

    lap() {
        laptime=`echo "$1" | sed -n 's/.*real[^0-9.]*\(.*\)/\1/p'`
        [ ! "$laptime" -o "$laptime" = "0.00" ] && return
        # Signals too frequent.
        laptotal=`echo $laptime+0$laptotal | bc`
        if [ "$2" = "display" ]; then
            lapcount=`echo 0$lapcount+1 | bc`
            laptime=`fmt_seconds $laptotal`
            echo $laptime "($lapcount)"
            lapped="true"
            laptotal="0"
        fi
    }

    echo -n "Space for lap | ? for split | Ctrl-C to stop | Space to start...">&2

    while true; do
        trap true INT QUIT  # Set signal handlers.
        laptime=`/usr/bin/time -p 2>&1 cat >/dev/null`
        ret=$?
        trap '' INT QUIT    # Ignore signals within this script.
        if [ $ret -eq 1 -o $ret -eq 2 -o $ret -eq 130 ]; then # SIGINT = stop
            [ ! "$start" ] && { echo >&2; exit; }
            stop
        elif [ $ret -eq 3 -o $ret -eq 131 ]; then             # SIGQUIT = lap
            if [ ! "$start" ]; then
                start=`now` || exit 1
                echo >&2
                continue
            fi
            lap "$laptime" "display"
        else                # eof = split
            [ ! "$start" ] && continue
            total
            lap "$laptime"  # Update laptotal.
        fi
    done

    exit $?

Example A-44. An all-purpose shell scripting homework assignment solution

    #!/bin/bash
    #  homework.sh: All-purpose homework assignment solution.
    #  Author: M. Leo Cooper
    #  If you substitute your own name as author, then it is plagiarism,
    #+ possibly a lesser sin than cheating on your homework!
    #  License: Public Domain

    #  This script may be turned in to your instructor
    #+ in fulfillment of ALL shell scripting homework assignments.
    #  It's sparsely commented, but you, the student, can easily remedy that.
    #  The script author repudiates all responsibility!

    DLA=1
    P1=2
    P2=4
    P3=7
    PP1=0
    PP2=8
    MAXL=9
    E_LZY=99

    declare -a L
    L[0]="3 4 0 17 29 8 13 18 19 17 20 2 19 14 17 28"
    L[1]="8 29 12 14 18 19 29 4 12 15 7 0 19 8 2 0 11 11 24 29 17 4 6 17 4 19"
    L[2]="29 19 7 0 19 29 8 29 7 0 21 4 29 13 4 6 11 4 2 19 4 3"
    L[3]="19 14 29 2 14 12 15 11 4 19 4 29 19 7 8 18 29"
    L[4]="18 2 7 14 14 11 22 14 17 10 29 0 18 18 8 6 13 12 4 13 19 26"
    L[5]="15 11 4 0 18 4 29 0 2 2 4 15 19 29 12 24 29 7 20 12 1 11 4 29"
    L[6]="4 23 2 20 18 4 29 14 5 29 4 6 17 4 6 8 14 20 18 29"
    L[7]="11 0 25 8 13 4 18 18 27"
    L[8]="0 13 3 29 6 17 0 3 4 29 12 4 29 0 2 2 14 17 3 8 13 6 11 24 26"
    L[9]="19 7 0 13 10 29 24 14 20 26"

    declare -a \
    alph=( A B C D E F G H I J K L M N O P Q R S T U V W X Y Z . , : ' ' )

    pt_lt ()
    {
      echo -n "${alph[$1]}"
      echo -n -e "\a"
      sleep $DLA
    }

    b_r ()
    {
     echo -e '\E[31;48m\033[1m'
    }

    cr ()
    {
     echo -e "\a"
     sleep $DLA
    }

    restore ()
    {
      echo -e '\033[0m'            # Bold off.
      tput sgr0                    # Normal.
    }

    p_l ()
    {
      for ltr in $1
      do
        pt_lt "$ltr"
      done
    }

    # ----------------------
    b_r

    for i in $(seq 0 $MAXL)
    do
      p_l "${L[i]}"
      if [[ "$i" -eq "$P1" || "$i" -eq "$P2" || "$i" -eq "$P3" ]]
      then
        cr
      elif [[ "$i" -eq "$PP1" || "$i" -eq "$PP2" ]]
      then
        cr; cr
      fi
    done

    restore
    # ----------------------

    echo

    exit $E_LZY

    #  A typical example of an obfuscated script that is difficult
    #+ to understand, and frustrating to maintain.
    #  In your career as a sysadmin, you'll run into these critters
    #+ all too often.

Example A-45. The Knight's Tour

    #!/bin/bash
    # ktour.sh

    # author: mendel cooper
    # reldate: 12 Jan 2009
    # license: public domain
    # (Not much sense GPLing something that's pretty much in the common
    #+ domain anyhow.)

    ###################################################################
    #             The Knight's Tour, a classic problem.               #
    #             =====================================               #
    #  The knight must move onto every square of the chess board,     #
    #  but cannot revisit any square he has already visited.          #
    #                                                                 #
    #  And just why is Sir Knight unwelcome for a return visit?       #
    #  Could it be that he has a habit of partying into the wee hours #
    #+ of the morning?                                                #
    #  Possibly he leaves pizza crusts in the bed, empty beer bottles #
    #+ all over the floor, and clogs the plumbing. . . .              #
    #                                                                 #
    #  -------------------------------------------------------------  #
    #                                                                 #
    #  Usage: ktour.sh [start-square] [stupid]                        #
    #                                                                 #
    #  Note that start-square can be a square number                  #
    #+ in the range 0 - 63 ... or                                     #
    #  a square designator in conventional chess notation,            #
    #  such as a1, f5, h3, etc.                                       #
    #                                                                 #
    #  If start-square-number not supplied,                           #
    #+ then starts on a random square somewhere on the board.         #
    #                                                                 #
    # "stupid" as second parameter sets the stupid strategy.          #
    #                                                                 #
    #  Examples:                                                      #
    #  ktour.sh 23          starts on square #23 (h3)                 #
    #  ktour.sh g6 stupid   starts on square #46,                     #
    #                       using "stupid" (non-Warnsdorff) strategy. #
    ###################################################################

    DEBUG=      # Set this to echo debugging info to stdout.
    SUCCESS=0
    FAIL=99
    BADMOVE=-999
    FAILURE=1
    LINELEN=21  # How many moves to display per line.
    # ---------------------------------------- #
    # Board array params
    ROWS=8   # 8 x 8 board.
    COLS=8
    let "SQUARES = $ROWS * $COLS"
    let "MAX = $SQUARES - 1"
    MIN=0
    # 64 squares on board, indexed from 0 to 63.

    VISITED=1
    UNVISITED=-1
    UNVSYM="##"
    # ---------------------------------------- #
    # Global variables.
    startpos=    # Starting position (square #, 0 - 63).
    currpos=     # Current position.
    movenum=     # Move number.
    CRITPOS=37   # Have to patch for f5 starting position!

    declare -i board
    # Use a one-dimensional array to simulate a two-dimensional one.
    # This can make life difficult and result in ugly kludges; see below.
    declare -i moves  # Offsets from current knight position.

    initialize_board ()
    {
      local idx

      for idx in {0..63}
      do
        board[$idx]=$UNVISITED
      done
    }

    print_board ()
    {
      local idx

      echo "    _____________________________________"
      for row in {7..0}               #  Reverse order of rows ...
      do                              #+ so it prints in chessboard order.
        let "rownum = $row + 1"       #  Start numbering rows at 1.
        echo -n "$rownum  |"          #  Mark board edge with border and
        for column in {0..7}          #+ "algebraic notation."
        do
          let "idx = $ROWS*$row + $column"
          if [ ${board[idx]} -eq $UNVISITED ]
          then
            echo -n "$UNVSYM   "      ##
          else                        # Mark square with move number.
            printf "%02d " "${board[idx]}"; echo -n "  "
          fi
        done
        echo -e -n "\b\b\b|"  # \b is a backspace.
        echo                  # -e enables echoing escaped chars.
      done

      echo "    -------------------------------------"
      echo "     a    b    c    d    e    f    g    h"
    }

    failure()
    { # Whine, then bail out.
      echo
      print_board
      echo
      echo    "   Waah!!! Ran out of squares to move to!"
      echo -n "   Knight's Tour attempt ended"
      echo    " on $(to_algebraic $currpos) [square #$currpos]"
      echo    "   after just $movenum moves!"
      echo
      exit $FAIL
    }

    xlat_coords ()   #  Translate x/y coordinates to board position
    {                #+ (board-array element #).
      #  For user input of starting board position as x/y coords.
      #  This function not used in initial release of ktour.sh.
      #  May be used in an updated version, for compatibility with
      #+ standard implementation of the Knight's Tour in C, Python, etc.
      if [ -z "$1" -o -z "$2" ]
      then
        return $FAIL
      fi

      local xc=$1
      local yc=$2

      let "board_index = $xc * $ROWS + yc"

      if [ $board_index -lt $MIN -o $board_index -gt $MAX ]
      then
        return $FAIL    # Strayed off the board!
      else
        return $board_index
      fi
    }

    to_algebraic ()   #  Translate board position (board-array element #)
    {                 #+ to standard algebraic notation used by chess players.
      if [ -z "$1" ]
      then
        return $FAIL
      fi

      local element_no=$1   # Numerical board position.
      local col_arr=( a b c d e f g h )
      local row_arr=( 1 2 3 4 5 6 7 8 )

      let "row_no = $element_no / $ROWS"
      let "col_no = $element_no % $ROWS"
      t1=${col_arr[col_no]}; t2=${row_arr[row_no]}
      local apos=$t1$t2   # Concatenate.
      echo $apos
    }

    from_algebraic ()   #  Translate standard algebraic chess notation
    {                   #+ to numerical board position (board-array element #).
                        #  Or recognize numerical input & return it unchanged.
      if [ -z "$1" ]
      then
        return $FAIL
      fi   # If no command-line arg, then will default to random start pos.

      local ix
      local ix_count=0
      local b_index     # Board index [0-63]
      local alpos="$1"

      arow=${alpos:0:1} # position = 0, length = 1
      acol=${alpos:1:1}

      if [[ $arow =~ [[:digit:]] ]]   #  Numerical input?
      then       #  POSIX char class
        if [[ $acol =~ [[:alpha:]] ]] # Number followed by a letter? Illegal!
          then return $FAIL
        else if [ $alpos -gt $MAX ]   # Off board?
          then return $FAIL
        else return $alpos            #  Return digit(s) unchanged . . .
          fi                          #+ if within range.
        fi
      fi

      if [[ $acol -eq $MIN || $acol -gt $ROWS ]]
      then        # Outside of range 1 - 8?
        return $FAIL
      fi

      for ix in a b c d e f g h
      do  # Convert column letter to column number.
       if [ "$arow" = "$ix" ]
       then
         break
       fi
      ((ix_count++))    # Find index count.
      done

      ((acol--))        # Decrementing converts to zero-based array.
      let "b_index = $ix_count + $acol * $ROWS"

      if [ $b_index -gt $MAX ]   # Off board?
      then
        return $FAIL
      fi

      return $b_index

    }

    generate_moves ()   #  Calculate all valid knight moves,
    {                   #+ relative to current position ($1),
                        #+ and store in ${moves} array.
      local kt_hop=1    #  One square  :: short leg of knight move.
      local kt_skip=2   #  Two squares :: long leg  of knight move.
      local valmov=0    #  Valid moves.
      local row_pos; let "row_pos = $1 % $COLS"

      let "move1 = -$kt_skip + $ROWS"           # 2 sideways to-the-left,  1 up
        if [[ `expr $row_pos - $kt_skip` -lt $MIN ]]   # An ugly, ugly kludge!
        then                                           # Can't move off board.
          move1=$BADMOVE                               # Not even temporarily.
        else
          ((valmov++))
        fi
      let "move2 = -$kt_hop + $kt_skip * $ROWS" # 1 sideways to-the-left,  2 up
        if [[ `expr $row_pos - $kt_hop` -lt $MIN ]]    # Kludge continued ...
        then
          move2=$BADMOVE
        else
          ((valmov++))
        fi
      let "move3 =  $kt_hop + $kt_skip * $ROWS" # 1 sideways to-the-right, 2 up
        if [[ `expr $row_pos + $kt_hop` -ge $COLS ]]
        then
          move3=$BADMOVE
        else
          ((valmov++))
        fi
      let "move4 =  $kt_skip + $ROWS"           # 2 sideways to-the-right, 1 up
        if [[ `expr $row_pos + $kt_skip` -ge $COLS ]]
        then
          move4=$BADMOVE
        else
          ((valmov++))
        fi
      let "move5 =  $kt_skip - $ROWS"           # 2 sideways to-the-right, 1 dn
        if [[ `expr $row_pos + $kt_skip` -ge $COLS ]]
        then
          move5=$BADMOVE
        else
          ((valmov++))
        fi
      let "move6 =  $kt_hop - $kt_skip * $ROWS" # 1 sideways to-the-right, 2 dn
        if [[ `expr $row_pos + $kt_hop` -ge $COLS ]]
        then
          move6=$BADMOVE
        else
          ((valmov++))
        fi
      let "move7 = -$kt_hop - $kt_skip * $ROWS" # 1 sideways to-the-left,  2 dn
        if [[ `expr $row_pos - $kt_hop` -lt $MIN ]]
        then
          move7=$BADMOVE
        else
          ((valmov++))
        fi
      let "move8 = -$kt_skip - $ROWS"           # 2 sideways to-the-left,  1 dn
        if [[ `expr $row_pos - $kt_skip` -lt $MIN ]]
        then
          move8=$BADMOVE
        else
          ((valmov++))
        fi   # There must be a better way to do this.

      local m=( $valmov $move1 $move2 $move3 $move4 $move5 $move6 $move7 $move8 )
      # ${moves[0]} = number of valid moves.
      # ${moves[1]} ... ${moves[8]} = possible moves.
      echo "${m[*]}"    # Elements of array to stdout for capture in a var.

    }

    is_on_board ()  # Is position actually on the board?
    {
      if [[ "$1" -lt "$MIN" || "$1" -gt "$MAX" ]]
      then
        return $FAILURE
      else
        return $SUCCESS
      fi
    }

    do_move ()      # Move the knight!
    {
      local valid_moves=0
      local aapos
      currposl="$1"
      lmin=$ROWS
      iex=0
      squarel=
      mpm=
      mov=
      declare -a p_moves

      ########################## DECIDE-MOVE #############################
      if [ $startpos -ne $CRITPOS ]
      then   # CRITPOS = square #37
        decide_move
      else                     # Needs a special patch for startpos=37 !!!
        decide_move_patched    # Why this particular move and no other ???
      fi
      ####################################################################

      (( ++movenum ))          # Increment move count.
      let "square = $currposl + ${moves[iex]}"

      ##################    DEBUG    ###############
      if [ "$DEBUG" ]
        then debug   # Echo debugging information.
      fi
      ##############################################

      if [[ "$square" -gt $MAX || "$square" -lt $MIN ||
            ${board[square]} -ne $UNVISITED ]]
      then
        (( --movenum ))              #  Decrement move count,
        echo "RAN OUT OF SQUARES!!!" #+ since previous one was invalid.
        return $FAIL
      fi

      board[square]=$movenum
      currpos=$square       # Update current position.
      ((valid_moves++));    # moves[0]=$valid_moves
      aapos=$(to_algebraic $square)
      echo -n "$aapos "
      test $(( $Moves % $LINELEN )) -eq 0 && echo
      # Print LINELEN=21 moves per line. A valid tour shows 3 complete lines.
      return $valid_moves   # Found a square to move to!
    }

    do_move_stupid()   #  Dingbat algorithm,
    {                  #+ courtesy of script author, *not* Warnsdorff.
      local valid_moves=0
      local movloc
      local squareloc
      local aapos
      local cposloc="$1"

      for movloc in {1..8}
      do       # Move to first-found unvisited square.
        let "squareloc = $cposloc + ${moves[movloc]}"
        is_on_board $squareloc
        if [ $? -eq $SUCCESS ] && [ ${board[squareloc]} -eq $UNVISITED ]
        then   # Add conditions to above if-test to improve algorithm.
          (( ++movenum ))
          board[squareloc]=$movenum
          currpos=$squareloc     # Update current position.
          ((valid_moves++));     # moves[0]=$valid_moves
          aapos=$(to_algebraic $squareloc)
          echo -n "$aapos "
          test $(( $Moves % $LINELEN )) -eq 0 && echo   # Print 21 moves/line.
          return $valid_moves    # Found a square to move to!
        fi
      done

      return $FAIL
      #  If no square found in all 8 loop iterations,
      #+ then Knight's Tour attempt ends in failure.

      #  Dingbat algorithm will typically fail after about 30 - 40 moves,
      #+ but executes _much_ faster than Warnsdorff's in do_move() function.
    }

    decide_move ()         #  Which move will we make?
    {                      #  But, fails on startpos=37 !!!
      for mov in {1..8}
      do
        let "squarel = $currposl + ${moves[mov]}"
        is_on_board $squarel
        if [[ $? -eq $SUCCESS && ${board[squarel]} -eq $UNVISITED ]]
        then   #  Find accessible square with least possible future moves.
               #  This is Warnsdorff's algorithm.
               #  What happens is that the knight wanders toward the outer edge
               #+ of the board, then pretty much spirals inward.
               #  Given two or more possible moves with same value of
               #+ least-possible-future-moves, this implementation chooses
               #+ the _first_ of those moves.
               #  This means that there is not necessarily a unique solution
               #+ for any given starting position.

          possible_moves $squarel
          mpm=$?
          p_moves[mov]=$mpm

          if [ $mpm -lt $lmin ]  # If less than previous minimum ...
          then #     ^^
            lmin=$mpm            # Update minimum.
            iex=$mov             # Save index.
          fi

        fi
      done
    }

    decide_move_patched ()         #  Decide which move to make,
    {  #        ^^^^^^^            #+ but only if startpos=37 !!!
      for mov in {1..8}
      do
        let "squarel = $currposl + ${moves[mov]}"
        is_on_board $squarel
        if [[ $? -eq $SUCCESS && ${board[squarel]} -eq $UNVISITED ]]
        then
          possible_moves $squarel
          mpm=$?
          p_moves[mov]=$mpm

          if [ $mpm -le $lmin ]  # If less-than-or equal to prev. minimum!
          then #     ^^
            lmin=$mpm
            iex=$mov
          fi

        fi
      done                       # There has to be a better way to do this.
    }

    possible_moves ()            #  Calculate number of possible moves,
    {                            #+ given the current position.

      if [ -z "$1" ]
      then
        return $FAIL
      fi

      local curr_pos=$1
      local valid_movl=0
      local icx=0
      local movl
      local sq
      declare -a movesloc

      movesloc=( $(generate_moves $curr_pos) )

      for movl in {1..8}
      do
        let "sq = $curr_pos + ${movesloc[movl]}"
        is_on_board $sq
        if [ $? -eq $SUCCESS ] && [ ${board[sq]} -eq $UNVISITED ]
        then
          ((valid_movl++));
        fi
      done

      return $valid_movl         # Found a square to move to!
    }

    strategy ()
    {
      echo

      if [ -n "$STUPID" ]
      then
        for Moves in {1..63}
        do
          cposl=$1
          moves=( $(generate_moves $currpos) )
          do_move_stupid "$currpos"
          if [ $? -eq $FAIL ]
          then
            failure
          fi
          done
      fi

      #  Don't need an "else" clause here,
      #+ because Stupid Strategy will always fail and exit!
      for Moves in {1..63}
      do
        cposl=$1
        moves=( $(generate_moves $currpos) )
        do_move "$currpos"
        if [ $? -eq $FAIL ]
        then
          failure
        fi

      done
            #  Could have condensed above two do-loops into a single one,
      echo  #+ but this would have slowed execution.

      print_board
      echo
      echo "Knight's Tour ends on $(to_algebraic $currpos) [square #$currpos]."
      return $SUCCESS
    }

    debug ()
    {       # Enable this by setting DEBUG=1 near beginning of script.
      local n

      echo "================================="
      echo "  At move number  $movenum:"
      echo " *** possible moves = $mpm ***"
    # echo "### square = $square ###"
      echo "lmin = $lmin"
      echo "${moves[@]}"

      for n in {1..8}
      do
        echo -n "($n):${p_moves[n]} "
      done

      echo
      echo "iex = $iex :: moves[iex] = ${moves[iex]}"
      echo "square = $square"
      echo "================================="
      echo
    } # Gives pretty complete status after ea. move.

    # =============================================================== #
    # int main () {
    from_algebraic "$1"
    startpos=$?
    if [ "$startpos" -eq "$FAIL" ]          # Okay even if no $1.
    then   #         ^^^^^^^^^^^              Okay even if input -lt 0.
      echo "No starting square specified (or illegal input)."
      let "startpos = $RANDOM % $SQUARES"   # 0 - 63 permissable range.
    fi

    if [ "$2" = "stupid" ]
    then
      STUPID=1
      echo -n "     ### Stupid Strategy ###"
    else
      STUPID=''
      echo -n "  *** Warnsdorff's Algorithm ***"
    fi

    initialize_board

    movenum=0
    board[startpos]=$movenum   # Mark each board square with move number.
    currpos=$startpos
    algpos=$(to_algebraic $startpos)

    echo; echo "Starting from $algpos [square #$startpos] ..."; echo
    echo -n "Moves:"

    strategy "$currpos"

    echo

    exit 0   # return 0;

    # }      # End of main() pseudo-function.
    # =============================================================== #

    # Exercises:
    # ---------
    #
    # 1) Extend this example to a 10 x 10 board or larger.
    # 2) Improve the "stupid strategy" by modifying the
    #    do_move_stupid function.
    #    Hint: Prevent straying into corner squares in early moves
    #          (the exact opposite of Warnsdorff's algorithm!).
    # 3) This script could stand considerable improvement and
    #    streamlining, especially in the poorly-written
    #    generate_moves() function
    #    and in the DECIDE-MOVE patch in the do_move() function.
    #    Must figure out why standard algorithm fails for startpos=37 ...
    #+   but _not_ on any other, including symmetrical startpos=26.
    #    Possibly, when calculating possible moves, counts the move back
    #+   to the originating square. If so, it might be a relatively easy fix.

Example A-46. Magic Squares

    #!/bin/bash
    # msquare.sh
    # Magic Square generator (odd-order squares only!)

    # Author: mendel cooper
    # reldate: 19 Jan. 2009
    # License: Public Domain
    # A C-program by Kwon Young Shin inspired this script.
    # See http://user.chollian.net/~brainstm/MagicSquare.htm ...

    # Definition: A "magic square" is a two-dimensional array
    #             of integers in which all the rows, columns,
    #             and *long* diagonals add up to the same number.
    #             Being "square," the array has the same number
    #             of rows and columns.
    # An example of a magic square of order 3 is:
    #   8  1  6
    #   3  5  7
    #   4  9  2
    # All the rows, columns, and long diagonals add up to 15.

    # Globals
    EVEN=2
    MAXSIZE=31   # 31 rows x 31 cols.
    E_usage=90   # Invocation error.
    dimension=
    declare -i square

    usage_message ()
    {
      echo "Usage: $0 square-size"
      echo "   ... where \"square-size\" is an ODD integer"
      echo "       in the range 3 - 31."
      #  Actually works for squares up to order 159,
      #+ but large squares will not display pretty-printed in a term window.
      #  Try increasing MAXSIZE, above.
      exit $E_usage
    }

    calculate ()       # Here's where the actual work gets done.
    {
      local row col index dimadj j k cell_val=1
      dimension=$1

      let "dimadj = $dimension * 3"; let "dimadj /= 2"   # x 1.5, then truncate.

      for ((j=0; j < dimension; j++))
      do
        for ((k=0; k < dimension; k++))
        do  # Calculate indices, then convert to 1-dim. array index.
            # Bash doesn't support multidimensional arrays. Pity.
          let "col = $k - $j + $dimadj"; let "col %= $dimension"
          let "row = $j * 2 - $k + $dimension"; let "row %= $dimension"
          let "index = $row*($dimension) + $col"
          square[$index]=cell_val; ((cell_val++))
        done
      done
    }     # Plain math, no visualization required.

    print_square ()               # Output square, one row at a time.
    {
      local row col idx d1
      let "d1 = $dimension - 1"   # Adjust for zero-indexed array.

      for row in $(seq 0 $d1)
      do

        for col in $(seq 0 $d1)
        do
          let "idx = $row * $dimension + $col"
          printf "%3d " "${square[idx]}"; echo -n "  "
        done   # Displays up to 13-order neatly in 80-column term window.

        echo   # Newline after each row.
      done
    }

    #################################################
    if [[ -z "$1" ]] || [[ "$1" -gt $MAXSIZE ]]
    then
      usage_message
    fi

    let "test_even = $1 % $EVEN"
    if [ $test_even -eq 0 ]
    then           # Can't handle even-order squares.
      usage_message
    fi

    calculate $1
    print_square   # echo "${square[@]}"   # DEBUG

    exit $?
    #################################################

    # Exercises:
    # ---------
    # 1) Add a function to calculate the sum of each row, column,
    #    and *long* diagonal. The sums must match.
    #    This is the "magic constant" of that particular order square.
    # 2) Have the print_square function auto-calculate how much space
    #    to allot between square elements for optimized display.
    #    This might require parameterizing the "printf" line.
    # 3) Add appropriate functions for generating magic squares
    #    with an *even* number of rows/columns.
    #    This is non-trivial(!).
    #    See the URL for Kwon Young Shin, above, for help.

Example A-47. Fifteen Puzzle

    #!/bin/bash
    # fifteen.sh

    # Classic "Fifteen Puzzle"
    # Author: Antonio Macchi
    # Lightly edited and commented by ABS Guide author.
    # Used in ABS Guide with permission. (Thanks!)

    #  The invention of the Fifteen Puzzle is attributed to either
    #+ Sam Loyd or Noyes Palmer Chapman.
    #  The puzzle was wildly popular in the late 19th-century.

    #  Object: Rearrange the numbers so they read in order,
    #+ from 1 - 15:   ________________
    #                |  1   2   3   4 |
    #                |  5   6   7   8 |
    #                |  9  10  11  12 |
    #                | 13  14  15     |
    #                 ----------------

    #######################
    # Constants           #
      SQUARES=16          #
      FAIL=70             #
      E_PREMATURE_EXIT=80 #
    #######################

    ########
    # Data #
    ########

    Puzzle=( 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 " " )

    #############
    # Functions #
    #############

    function swap
    {
      local tmp

      tmp=${Puzzle[$1]}
      Puzzle[$1]=${Puzzle[$2]}
      Puzzle[$2]=$tmp
    }

    function Jumble
    { # Scramble the pieces at beginning of round.
      local i pos1 pos2

      for i in {1..100}
      do
        pos1=$(( $RANDOM % $SQUARES))
        pos2=$(( $RANDOM % $SQUARES ))
        swap $pos1 $pos2
      done
    }

    function PrintPuzzle
    {
      local i1 i2 puzpos
      puzpos=0

      clear
      echo "Enter  quit  to exit."; echo   # Better that than Ctl-C.

      echo ",----.----.----.----."   # Top border.
      for i1 in {1..4}
      do
        for i2 in {1..4}
        do
          printf "| %2s " "${Puzzle[$puzpos]}"
          (( puzpos++ ))
        done
        echo "|"                     # Right-side border.
        test $i1 = 4 || echo "+----+----+----+----+"
      done
      echo "'----'----'----'----'"   # Bottom border.
    }

    function GetNum
    { # Test for valid input.
      local puznum garbage

      while true
      do
    	  echo "Moves: $moves" # Also counts invalid moves.
        read -p "Number to move: " puznum garbage
          if [ "$puznum" = "quit" ]; then echo; exit $E_PREMATURE_EXIT; fi
        test -z "$puznum" -o -n "${puznum//[0-9]/}" && continue
        test $puznum -gt 0 -a $puznum -lt $SQUARES && break
      done
      return $puznum
    }

    function GetPosFromNum
    { # $1 = puzzle-number
      local puzpos

      for puzpos in {0..15}
      do
        test "${Puzzle[$puzpos]}" = "$1" && break
      done
      return $puzpos
    }

    function Move
    { # $1=Puzzle-pos
      test $1 -gt 3 && test "${Puzzle[$(( $1 - 4 ))]}" = " "\
           && swap $1 $(( $1 - 4 )) && return 0
      test $(( $1%4 )) -ne 3 && test "${Puzzle[$(( $1 + 1 ))]}" = " "\
           && swap $1 $(( $1 + 1 )) && return 0
      test $1 -lt 12 && test "${Puzzle[$(( $1 + 4 ))]}" = " "\
           && swap $1 $(( $1 + 4 )) && return 0
      test $(( $1%4 )) -ne 0 && test "${Puzzle[$(( $1 - 1 ))]}" = " " &&\
           swap $1 $(( $1 - 1 )) && return 0
      return 1
    }

    function Solved
    {
      local pos

      for pos in {0..14}
      do
        test "${Puzzle[$pos]}" = $(( $pos + 1 )) || return $FAIL
        # Check whether number in each square = square number.
      done
      return 0   # Successful solution.
    }

    ################### MAIN () #######################{
    moves=0
    Jumble

    while true   # Loop continuously until puzzle solved.
    do
      echo; echo
      PrintPuzzle
      echo
      while true
      do
        GetNum
        puznum=$?
        GetPosFromNum $puznum
        puzpos=$?
        ((moves++))
        Move $puzpos && break
      done
      Solved && break
    done

    echo;echo
    PrintPuzzle
    echo; echo "BRAVO!"; echo

    exit 0
    ###################################################}

    #  Exercise:
    #  --------
    #  Rewrite the script to display the letters A - O,
    #+ rather than the numbers 1 - 15.

Example A-48. The Towers of Hanoi, graphic version

    #! /bin/bash
    # The Towers Of Hanoi
    # Original script (hanoi.bash) copyright (C) 2000 Amit Singh.
    # All Rights Reserved.
    # http://hanoi.kernelthread.com

    #  hanoi2.bash
    #  Version 2.00: modded for ASCII-graphic display.
    #  Version 2.01: fixed no command-line param bug.
    #  Uses code contributed by Antonio Macchi,
    #+ with heavy editing by ABS Guide author.
    #  This variant falls under the original copyright, see above.
    #  Used in ABS Guide with Amit Singh's permission (thanks!).

    ###   Variables && sanity check   ###

    E_NOPARAM=86
    E_BADPARAM=87            # Illegal no. of disks passed to script.
    E_NOEXIT=88

    DISKS=${1:-$E_NOPARAM}   # Must specify how many disks.
    Moves=0

    MWIDTH=7
    MARGIN=2
    # Arbitrary "magic" constants; work okay for relatively small # of disks.
    # BASEWIDTH=51   # Original code.
    let "basewidth = $MWIDTH * $DISKS + $MARGIN"       # "Base" beneath rods.
    # Above "algorithm" could likely stand improvement.

    ###   Display variables   ###
    let "disks1 = $DISKS - 1"
    let "spaces1 = $DISKS"
    let "spaces2 = 2 * $DISKS"

    let "lastmove_t = $DISKS - 1"                      # Final move?

    declare -a Rod1 Rod2 Rod3

    ###   #########################   ###

    function repeat  {  # $1=char $2=number of repetitions
      local n           # Repeat-print a character.

      for (( n=0; n<$2; n++ )); do
        echo -n "$1"
      done
    }

    function FromRod  {
      local rod summit weight sequence

      while true; do
        rod=$1
        test ${rod/[^123]/} || continue

        sequence=$(echo $(seq 0 $disks1 | tac))
        for summit in $sequence; do
          eval weight=\${Rod${rod}[$summit]}
          test $weight -ne 0 &&
               { echo "$rod $summit $weight"; return; }
        done
      done
    }

    function ToRod  { # $1=previous (FromRod) weight
      local rod firstfree weight sequence

      while true; do
        rod=$2
        test ${rod/[^123]} || continue

        sequence=$(echo $(seq 0 $disks1 | tac))
        for firstfree in $sequence; do
          eval weight=\${Rod${rod}[$firstfree]}
          test $weight -gt 0 && { (( firstfree++ )); break; }
        done
        test $weight -gt $1 -o $firstfree = 0 &&
             { echo "$rod $firstfree"; return; }
      done
    }

    function PrintRods  {
      local disk rod empty fill sp sequence

      repeat " " $spaces1
      echo -n "|"
      repeat " " $spaces2
      echo -n "|"
      repeat " " $spaces2
      echo "|"

      sequence=$(echo $(seq 0 $disks1 | tac))
      for disk in $sequence; do
        for rod in {1..3}; do
          eval empty=$(( $DISKS - (Rod${rod}[$disk] / 2) ))
          eval fill=\${Rod${rod}[$disk]}
          repeat " " $empty
          test $fill -gt 0 && repeat "*" $fill || echo -n "|"
          repeat " " $empty
        done
        echo
      done
      repeat "=" $basewidth   # Print "base" beneath rods.
      echo
    }

    display ()
    {
      echo
      PrintRods

      # Get rod-number, summit and weight
      first=( `FromRod $1` )
      eval Rod${first[0]}[${first[1]}]=0

      # Get rod-number and first-free position
      second=( `ToRod ${first[2]} $2` )
      eval Rod${second[0]}[${second[1]}]=${first[2]}

    echo; echo; echo
    if [ "${Rod3[lastmove_t]}" = 1 ]
    then   # Last move? If yes, then display final position.
        echo "+  Final Position: $Moves moves"; echo
        PrintRods
      fi
    }

    # From here down, almost the same as original (hanoi.bash) script.

    dohanoi() {   # Recursive function.
        case $1 in
        0)
            ;;
        *)
            dohanoi "$(($1-1))" $2 $4 $3
    	if [ "$Moves" -ne 0 ]
            then
    	  echo "+  Position after move $Moves"
            fi
            ((Moves++))
            echo -n "   Next move will be:  "
            echo $2 "-->" $3
              display $2 $3
            dohanoi "$(($1-1))" $4 $3 $2
            ;;
        esac
    }

    setup_arrays ()
    {
      local dim n elem

      let "dim1 = $1 - 1"
      elem=$dim1

      for n in $(seq 0 $dim1)
      do
       let "Rod1[$elem] = 2 * $n + 1"
       Rod2[$n]=0
       Rod3[$n]=0
       ((elem--))
      done
    }

    ###   Main   ###

    setup_arrays $DISKS
    echo; echo "+  Start Position"

    case $# in
        1) case $(($1>0)) in     # Must have at least one disk.
           1)
               disks=$1
               dohanoi $1 1 3 2
    #          Total moves = 2^n - 1, where n = number of disks.
    	   echo
               exit 0;
               ;;
           *)
               echo "$0: Illegal value for number of disks";
               exit $E_BADPARAM;
               ;;
           esac
        ;;
        *)
           clear
           echo "usage: $0 N"
           echo "       Where \"N\" is the number of disks."
           exit $E_NOPARAM;
           ;;
    esac

    exit $E_NOEXIT   # Shouldn't exit here.

    # Note:
    # Redirect script output to a file, otherwise it scrolls off display.

Example A-49. The Towers of Hanoi, alternate graphic version

    #! /bin/bash
    # The Towers Of Hanoi
    # Original script (hanoi.bash) copyright (C) 2000 Amit Singh.
    # All Rights Reserved.
    # http://hanoi.kernelthread.com

    #  hanoi2.bash
    #  Version 2: modded for ASCII-graphic display.
    #  Uses code contributed by Antonio Macchi,
    #+ with heavy editing by ABS Guide author.
    #  This variant also falls under the original copyright, see above.
    #  Used in ABS Guide with Amit Singh's permission (thanks!).

    #   Variables   #
    E_NOPARAM=86
    E_BADPARAM=87   # Illegal no. of disks passed to script.
    E_NOEXIT=88
    DELAY=2         # Interval, in seconds, between moves. Change, if desired.
    DISKS=$1
    Moves=0

    MWIDTH=7
    MARGIN=2
    # Arbitrary "magic" constants, work okay for relatively small # of disks.
    # BASEWIDTH=51   # Original code.
    let "basewidth = $MWIDTH * $DISKS + $MARGIN" # "Base" beneath rods.
    # Above "algorithm" could likely stand improvement.

    # Display variables.
    let "disks1 = $DISKS - 1"
    let "spaces1 = $DISKS"
    let "spaces2 = 2 * $DISKS"

    let "lastmove_t = $DISKS - 1"                # Final move?

    declare -a Rod1 Rod2 Rod3

    #################

    function repeat  {  # $1=char $2=number of repetitions
      local n           # Repeat-print a character.

      for (( n=0; n<$2; n++ )); do
        echo -n "$1"
      done
    }

    function FromRod  {
      local rod summit weight sequence

      while true; do
        rod=$1
        test ${rod/[^123]/} || continue

        sequence=$(echo $(seq 0 $disks1 | tac))
        for summit in $sequence; do
          eval weight=\${Rod${rod}[$summit]}
          test $weight -ne 0 &&
               { echo "$rod $summit $weight"; return; }
        done
      done
    }

    function ToRod  { # $1=previous (FromRod) weight
      local rod firstfree weight sequence

      while true; do
        rod=$2
        test ${rod/[^123]} || continue

        sequence=$(echo $(seq 0 $disks1 | tac))
        for firstfree in $sequence; do
          eval weight=\${Rod${rod}[$firstfree]}
          test $weight -gt 0 && { (( firstfree++ )); break; }
        done
        test $weight -gt $1 -o $firstfree = 0 &&
             { echo "$rod $firstfree"; return; }
      done
    }

    function PrintRods  {
      local disk rod empty fill sp sequence

      tput cup 5 0

      repeat " " $spaces1
      echo -n "|"
      repeat " " $spaces2
      echo -n "|"
      repeat " " $spaces2
      echo "|"

      sequence=$(echo $(seq 0 $disks1 | tac))
      for disk in $sequence; do
        for rod in {1..3}; do
          eval empty=$(( $DISKS - (Rod${rod}[$disk] / 2) ))
          eval fill=\${Rod${rod}[$disk]}
          repeat " " $empty
          test $fill -gt 0 && repeat "*" $fill || echo -n "|"
          repeat " " $empty
        done
        echo
      done
      repeat "=" $basewidth   # Print "base" beneath rods.
      echo
    }

    display ()
    {
      echo
      PrintRods

      # Get rod-number, summit and weight
      first=( `FromRod $1` )
      eval Rod${first[0]}[${first[1]}]=0

      # Get rod-number and first-free position
      second=( `ToRod ${first[2]} $2` )
      eval Rod${second[0]}[${second[1]}]=${first[2]}

      if [ "${Rod3[lastmove_t]}" = 1 ]
      then   # Last move? If yes, then display final position.
        tput cup 0 0
        echo; echo "+  Final Position: $Moves moves"
        PrintRods
      fi

      sleep $DELAY
    }

    # From here down, almost the same as original (hanoi.bash) script.

    dohanoi() {   # Recursive function.
        case $1 in
        0)
            ;;
        *)
            dohanoi "$(($1-1))" $2 $4 $3
    	if [ "$Moves" -ne 0 ]
            then
    	  tput cup 0 0
    	  echo; echo "+  Position after move $Moves"
            fi
            ((Moves++))
            echo -n "   Next move will be:  "
            echo $2 "-->" $3
            display $2 $3
            dohanoi "$(($1-1))" $4 $3 $2
            ;;
        esac
    }

    setup_arrays ()
    {
      local dim n elem

      let "dim1 = $1 - 1"
      elem=$dim1

      for n in $(seq 0 $dim1)
      do
       let "Rod1[$elem] = 2 * $n + 1"
       Rod2[$n]=0
       Rod3[$n]=0
       ((elem--))
      done
    }

    ###   Main   ###

    trap "tput cnorm" 0
    tput civis
    clear

    setup_arrays $DISKS

    tput cup 0 0
    echo; echo "+  Start Position"

    case $# in
        1) case $(($1>0)) in     # Must have at least one disk.
           1)
               disks=$1
               dohanoi $1 1 3 2
    #          Total moves = 2^n - 1, where n = # of disks.
    	   echo
               exit 0;
               ;;
           *)
               echo "$0: Illegal value for number of disks";
               exit $E_BADPARAM;
               ;;
           esac
        ;;
        *)
           echo "usage: $0 N"
           echo "       Where \"N\" is the number of disks."
           exit $E_NOPARAM;
           ;;
    esac

    exit $E_NOEXIT   # Shouldn't exit here.

    #  Exercise:
    #  --------
    #  There is a minor bug in the script that causes the display of
    #+ the next-to-last move to be skipped.
    #+ Fix this.

Example A-50. An alternate version of the getopt-simple.sh script

    #!/bin/bash
    # UseGetOpt.sh

    # Author: Peggy Russell <prusselltechgroup@gmail.com>

    UseGetOpt () {
      declare inputOptions
      declare -r E_OPTERR=85
      declare -r ScriptName=${0##*/}
      declare -r ShortOpts="adf:hlt"
      declare -r LongOpts="aoption,debug,file:,help,log,test"

    DoSomething () {
        echo "The function name is '${FUNCNAME}'"
        #  Recall that $FUNCNAME is an internal variable
        #+ holding the name of the function it is in.
      }

      inputOptions=$(getopt -o "${ShortOpts}" --long \
                  "${LongOpts}" --name "${ScriptName}" -- "${@}")

      if [[ ($? -ne 0) || ($# -eq 0) ]]; then
        echo "Usage: ${ScriptName} [-dhlt] {OPTION...}"
        exit $E_OPTERR
      fi

      eval set -- "${inputOptions}"

      # Only for educational purposes. Can be removed.
      #-----------------------------------------------
      echo "++ Test: Number of arguments: [$#]"
      echo '++ Test: Looping through "$@"'
      for a in "$@"; do
        echo "  ++ [$a]"
      done
      #-----------------------------------------------

      while true; do
        case "${1}" in
          --aoption | -a)  # Argument found.
            echo "Option [$1]"
            ;;

          --debug | -d)    # Enable informational messages.
            echo "Option [$1] Debugging enabled"
            ;;

          --file | -f)     #  Check for optional argument.
            case "$2" in   #+ Double colon is optional argument.
              "")          #  Not there.
                  echo "Option [$1] Use default"
                  shift
                  ;;

              *) # Got it
                 echo "Option [$1] Using input [$2]"
                 shift
                 ;;

            esac
            DoSomething
            ;;

          --log | -l) # Enable Logging.
            echo "Option [$1] Logging enabled"
            ;;

          --test | -t) # Enable testing.
            echo "Option [$1] Testing enabled"
            ;;

          --help | -h)
            echo "Option [$1] Display help"
            break
            ;;

          --)   # Done! $# is argument number for "--", $@ is "--"
            echo "Option [$1] Dash Dash"
            break
            ;;

           *)
            echo "Major internal error!"
            exit 8
            ;;

        esac
        echo "Number of arguments: [$#]"
        shift
      done

      shift
      # Only for educational purposes. Can be removed.
      #----------------------------------------------------------------------
      echo "++ Test: Number of arguments after \"--\" is [$#] They are: [$@]"
      echo '++ Test: Looping through "$@"'
      for a in "$@"; do
        echo "  ++ [$a]"
      done
      #----------------------------------------------------------------------

    }

    ################################### M A I N ########################
    #  If you remove "function UseGetOpt () {" and corresponding "}",
    #+ you can uncomment the "exit 0" line below, and invoke this script
    #+ with the various options from the command-line.
    #-------------------------------------------------------------------
    # exit 0

    echo "Test 1"
    UseGetOpt -f myfile one "two three" four

    echo;echo "Test 2"
    UseGetOpt -h

    echo;echo "Test 3 - Short Options"
    UseGetOpt -adltf myfile  anotherfile

    echo;echo "Test 4 - Long Options"
    UseGetOpt --aoption --debug --log --test --file myfile anotherfile

    exit

Example A-51. The version of the UseGetOpt.sh example used in the Tab Expansion appendix

    #!/bin/bash

    #  UseGetOpt-2.sh
    #  Modified version of the script for illustrating tab-expansion
    #+ of command-line options.
    #  See the "Introduction to Tab Expansion" appendix.

    #  Possible options: -a -d -f -l -t -h
    #+                   --aoption, --debug --file --log --test -- help --

    #  Author of original script: Peggy Russell <prusselltechgroup@gmail.com>

    # UseGetOpt () {
      declare inputOptions
      declare -r E_OPTERR=85
      declare -r ScriptName=${0##*/}
      declare -r ShortOpts="adf:hlt"
      declare -r LongOpts="aoption,debug,file:,help,log,test"

    DoSomething () {
        echo "The function name is '${FUNCNAME}'"
      }

      inputOptions=$(getopt -o "${ShortOpts}" --long \
                  "${LongOpts}" --name "${ScriptName}" -- "${@}")

      if [[ ($? -ne 0) || ($# -eq 0) ]]; then
        echo "Usage: ${ScriptName} [-dhlt] {OPTION...}"
        exit $E_OPTERR
      fi

      eval set -- "${inputOptions}"

      while true; do
        case "${1}" in
          --aoption | -a)  # Argument found.
            echo "Option [$1]"
            ;;

          --debug | -d)    # Enable informational messages.
            echo "Option [$1] Debugging enabled"
            ;;

          --file | -f)     #  Check for optional argument.
            case "$2" in   #+ Double colon is optional argument.
              "")          #  Not there.
                  echo "Option [$1] Use default"
                  shift
                  ;;

              *) # Got it
                 echo "Option [$1] Using input [$2]"
                 shift
                 ;;

            esac
            DoSomething
            ;;

          --log | -l) # Enable Logging.
            echo "Option [$1] Logging enabled"
            ;;

          --test | -t) # Enable testing.
            echo "Option [$1] Testing enabled"
            ;;

          --help | -h)
            echo "Option [$1] Display help"
            break
            ;;

          --)   # Done! $# is argument number for "--", $@ is "--"
            echo "Option [$1] Dash Dash"
            break
            ;;

           *)
            echo "Major internal error!"
            exit 8
            ;;

        esac
        echo "Number of arguments: [$#]"
        shift
      done

      shift

    #  }

    exit

Example A-52. Cycling through all the possible color backgrounds

    #!/bin/bash

    # show-all-colors.sh
    # Displays all 256 possible background colors, using ANSI escape sequences.
    # Author: Chetankumar Phulpagare
    # Used in ABS Guide with permission.

    T1=8
    T2=6
    T3=36
    offset=0

    for num1 in {0..7}
    do {
       for num2 in {0,1}
           do {
              shownum=`echo "$offset + $T1 * ${num2} + $num1" | bc`
              echo -en "\E[0;48;5;${shownum}m color ${shownum} \E[0m"
              }
           done
       echo
       }
    done

    offset=16
    for num1 in {0..5}
    do {
       for num2 in {0..5}
           do {
              for num3 in {0..5}
                  do {
                     shownum=`echo "$offset + $T2 * ${num3} \
                     + $num2 + $T3 * ${num1}" | bc`
                     echo -en "\E[0;48;5;${shownum}m color ${shownum} \E[0m"
                     }
                   done
              echo
              }
           done
    }
    done

    offset=232
    for num1 in {0..23}
    do {
       shownum=`expr $offset + $num1`
       echo -en "\E[0;48;5;${shownum}m ${shownum}\E[0m"
    }
    done

    echo

Example A-53. Morse Code Practice

    #!/bin/bash
    # sam.sh, v. .01a
    # Still Another Morse (code training script)
    # With profuse apologies to Sam (F.B.) Morse.
    # Author: Mendel Cooper
    # License: GPL3
    # Reldate: 05/25/11

    # Morse code training script.
    # Converts arguments to audible dots and dashes.
    # Note: lowercase input only at this time.

    # Get the wav files from the source tarball:
    # http://bash.deta.in/abs-guide-latest.tar.bz2
    DOT='soundfiles/dot.wav'
    DASH='soundfiles/dash.wav'
    # Maybe move soundfiles to /usr/local/sounds?

    LETTERSPACE=300000  # Microseconds.
    WORDSPACE=980000
    # Nice and slow, for beginners. Maybe 5 wpm?

    EXIT_MSG="May the Morse be with you!"
    E_NOARGS=75         # No command-line args?

    declare -A morse    # Associative array!
    # ======================================= #
    morse[a]="dot; dash"
    morse[b]="dash; dot; dot; dot"
    morse[c]="dash; dot; dash; dot"
    morse[d]="dash; dot; dot"
    morse[e]="dot"
    morse[f]="dot; dot; dash; dot"
    morse[g]="dash; dash; dot"
    morse[h]="dot; dot; dot; dot"
    morse[i]="dot; dot;"
    morse[j]="dot; dash; dash; dash"
    morse[k]="dash; dot; dash"
    morse[l]="dot; dash; dot; dot"
    morse[m]="dash; dash"
    morse[n]="dash; dot"
    morse[o]="dash; dash; dash"
    morse[p]="dot; dash; dash; dot"
    morse[q]="dash; dash; dot; dash"
    morse[r]="dot; dash; dot"
    morse[s]="dot; dot; dot"
    morse[t]="dash"
    morse[u]="dot; dot; dash"
    morse[v]="dot; dot; dot; dash"
    morse[w]="dot; dash; dash"
    morse[x]="dash; dot; dot; dash"
    morse[y]="dash; dot; dash; dash"
    morse[z]="dash; dash; dot; dot"
    morse[0]="dash; dash; dash; dash; dash"
    morse[1]="dot; dash; dash; dash; dash"
    morse[2]="dot; dot; dash; dash; dash"
    morse[3]="dot; dot; dot; dash; dash"
    morse[4]="dot; dot; dot; dot; dash"
    morse[5]="dot; dot; dot; dot; dot"
    morse[6]="dash; dot; dot; dot; dot"
    morse[7]="dash; dash; dot; dot; dot"
    morse[8]="dash; dash; dash; dot; dot"
    morse[9]="dash; dash; dash; dash; dot"
    # The following must be escaped or quoted.
    morse[?]="dot; dot; dash; dash; dot; dot"
    morse[.]="dot; dash; dot; dash; dot; dash"
    morse[,]="dash; dash; dot; dot; dash; dash"
    morse[/]="dash; dot; dot; dash; dot"
    morse[\@]="dot; dash; dash; dot; dash; dot"
    # ======================================= #

    play_letter ()
    {
      eval ${morse[$1]}   # Play dots, dashes from appropriate sound files.
      # Why is 'eval' necessary here?
      usleep $LETTERSPACE # Pause in between letters.
    }

    extract_letters ()
    {                     # Slice string apart, letter by letter.
      local pos=0         # Starting at left end of string.
      local len=1         # One letter at a time.
      strlen=${#1}

      while [ $pos -lt $strlen ]
      do
        letter=${1:pos:len}
        #      ^^^^^^^^^^^^    See Chapter 10.1.
        play_letter $letter
        echo -n "*"       #    Mark letter just played.
        ((pos++))
      done
    }

    ######### Play the sounds ############
    dot()  { aplay "$DOT" 2&>/dev/null;  }
    dash() { aplay "$DASH" 2&>/dev/null; }
    ######################################

    no_args ()
    {
        declare -a usage
        usage=( $0 word1 word2 ... )

        echo "Usage:"; echo
        echo ${usage[*]}
        for index in 0 1 2 3
        do
          extract_letters ${usage[index]}
          usleep $WORDSPACE
          echo -n " "     # Print space between words.
        done
    #   echo "Usage: $0 word1 word2 ... "
        echo; echo
    }

    # int main()
    # {

    clear                 # Clear the terminal screen.
    echo "            SAM"
    echo "Still Another Morse code trainer"
    echo "    Author: Mendel Cooper"
    echo; echo;

    if [ -z "$1" ]
    then
      no_args
      echo; echo; echo "$EXIT_MSG"; echo
      exit $E_NOARGS
    fi

    echo; echo "$*"       # Print text that will be played.

    until [ -z "$1" ]
    do
      extract_letters $1
      shift           # On to next word.
      usleep $WORDSPACE
      echo -n " "     # Print space between words.
    done

    echo; echo; echo "$EXIT_MSG"; echo

    exit 0
    # }

    #  Exercises:
    #  ---------
    #  1) Have the script accept either lowercase or uppercase words
    #+    as arguments. Hint: Use 'tr' . . .
    #  2) Have the script optionally accept input from a text file.

Example A-54. Base64 encoding/decoding

    #!/bin/bash
    # base64.sh: Bash implementation of Base64 encoding and decoding.
    #
    # Copyright (c) 2011 vladz <vladz@devzero.fr>
    # Used in ABSG with permission (thanks!).
    #
    #  Encode or decode original Base64 (and also Base64url)
    #+ from STDIN to STDOUT.
    #
    #    Usage:
    #
    #    Encode
    #    $ ./base64.sh < binary-file > binary-file.base64
    #    Decode
    #    $ ./base64.sh -d < binary-file.base64 > binary-file
    #
    # Reference:
    #
    #    [1]  RFC4648 - "The Base16, Base32, and Base64 Data Encodings"
    #         http://tools.ietf.org/html/rfc4648#section-5

    # The base64_charset[] array contains entire base64 charset,
    # and additionally the character "=" ...
    base64_charset=( {A..Z} {a..z} {0..9} + / = )
                    # Nice illustration of brace expansion.

    #  Uncomment the ### line below to use base64url encoding instead of
    #+ original base64.
    ### base64_charset=( {A..Z} {a..z} {0..9} - _ = )

    #  Output text width when encoding
    #+ (64 characters, just like openssl output).
    text_width=64

    function display_base64_char {
    #  Convert a 6-bit number (between 0 and 63) into its corresponding values
    #+ in Base64, then display the result with the specified text width.
      printf "${base64_charset[$1]}"; (( width++ ))
      (( width % text_width == 0 )) && printf "\n"
    }

    function encode_base64 {
    # Encode three 8-bit hexadecimal codes into four 6-bit numbers.
      #    We need two local int array variables:
      #    c8[]: to store the codes of the 8-bit characters to encode
      #    c6[]: to store the corresponding encoded values on 6-bit
      declare -a -i c8 c6

      #  Convert hexadecimal to decimal.
      c8=( $(printf "ibase=16; ${1:0:2}\n${1:2:2}\n${1:4:2}\n" | bc) )

      #  Let's play with bitwise operators
      #+ (3x8-bit into 4x6-bits conversion).
      (( c6[0] = c8[0] >> 2 ))
      (( c6[1] = ((c8[0] &  3) << 4) | (c8[1] >> 4) ))

      # The following operations depend on the c8 element number.
      case ${#c8[*]} in
        3) (( c6[2] = ((c8[1] & 15) << 2) | (c8[2] >> 6) ))
           (( c6[3] = c8[2] & 63 )) ;;
        2) (( c6[2] = (c8[1] & 15) << 2 ))
           (( c6[3] = 64 )) ;;
        1) (( c6[2] = c6[3] = 64 )) ;;
      esac

      for char in ${c6[@]}; do
        display_base64_char ${char}
      done
    }

    function decode_base64 {
    # Decode four base64 characters into three hexadecimal ASCII characters.
      #  c8[]: to store the codes of the 8-bit characters
      #  c6[]: to store the corresponding Base64 values on 6-bit
      declare -a -i c8 c6

      # Find decimal value corresponding to the current base64 character.
      for current_char in ${1:0:1} ${1:1:1} ${1:2:1} ${1:3:1}; do
         [ "${current_char}" = "=" ] && break

         position=0
         while [ "${current_char}" != "${base64_charset[${position}]}" ]; do
            (( position++ ))
         done

         c6=( ${c6[*]} ${position} )
      done

      #  Let's play with bitwise operators
      #+ (4x8-bit into 3x6-bits conversion).
      (( c8[0] = (c6[0] << 2) | (c6[1] >> 4) ))

      # The next operations depends on the c6 elements number.
      case ${#c6[*]} in
        3) (( c8[1] = ( (c6[1] & 15) << 4) | (c6[2] >> 2) ))
           (( c8[2] = (c6[2] & 3) << 6 )); unset c8[2] ;;
        4) (( c8[1] = ( (c6[1] & 15) << 4) | (c6[2] >> 2) ))
           (( c8[2] = ( (c6[2] &  3) << 6) |  c6[3] )) ;;
      esac

      for char in ${c8[*]}; do
         printf "\x$(printf "%x" ${char})"
      done
    }

    # main ()

    if [ "$1" = "-d" ]; then   # decode

      # Reformat STDIN in pseudo 4x6-bit groups.
      content=$(cat - | tr -d "\n" | sed -r "s/(.{4})/\1 /g")

      for chars in ${content}; do decode_base64 ${chars}; done

    else
      # Make a hexdump of stdin and reformat in 3-byte groups.
      content=$(cat - | xxd -ps -u | sed -r "s/(\w{6})/\1 /g" |
                tr -d "\n")

      for chars in ${content}; do encode_base64 ${chars}; done

      echo

    fi

Example A-55. The Gronsfeld Cipher

    #!/bin/bash
    # gronsfeld.bash

    # License: GPL3
    # Reldate 06/23/11

    #  This is an implementation of the Gronsfeld Cipher.
    #  It's essentially a stripped-down variant of the
    #+ polyalphabetic Vigenère Tableau, but with only 10 alphabets.
    #  The classic Gronsfeld has a numeric sequence as the key word,
    #+ but here we substitute a letter string, for ease of use.
    #  Allegedly, this cipher was invented by the eponymous Count Gronsfeld
    #+ in the 17th Century. It was at one time considered to be unbreakable.
    #  Note that this is ###not### a secure cipher by modern standards.

    #  Global Variables  #
    Enc_suffix="29379"   #  Encrypted text output with this 5-digit suffix.
                         #  This functions as a decryption flag,
                         #+ and when used to generate passwords adds security.
    Default_key="gronsfeldk"
                         #  The script uses this if key not entered below
                         #  (at "Keychain").
                         #  Change the above two values frequently
                         #+ for added security.

    GROUPLEN=5           #  Output in groups of 5 letters, per tradition.
    alpha1=( abcdefghijklmnopqrstuvwxyz )
    alpha2=( {A..Z} )    #  Output in all caps, per tradition.
                         #  Use   alpha2=( {a..z} )   for password generator.
    wraplen=26           #  Wrap around if past end of alphabet.
    dflag=               #  Decrypt flag (set if $Enc_suffix present).
    E_NOARGS=76          #  Missing command-line args?
    DEBUG=77             #  Debugging flag.
    declare -a offsets   #  This array holds the numeric shift values for
                         #+ encryption/decryption.

    ########Keychain#########
    key=  ### Put key here!!!
          # 10 characters!
    #########################

    # Function
    : ()
    { # Encrypt or decrypt, depending on whether $dflag is set.
      # Why ": ()" as a function name? Just to prove that it can be done.

      local idx keydx mlen off1 shft
      local plaintext="$1"
      local mlen=${#plaintext}

    for (( idx=0; idx<$mlen; idx++ ))
    do
      let "keydx = $idx % $keylen"
      shft=${offsets[keydx]}

      if [ -n "$dflag" ]
      then                  # Decrypt!
        let "off1 = $(expr index "${alpha1[*]}" ${plaintext:idx:1}) - $shft"
        # Shift backward to decrypt.
      else                  # Encrypt!
        let "off1 = $(expr index "${alpha1[*]}" ${plaintext:idx:1}) + $shft"
        # Shift forward to encrypt.
        test $(( $idx % $GROUPLEN)) = 0 && echo -n " "  # Groups of 5 letters.
        #  Comment out above line for output as a string without whitespace,
        #+ for example, if using the script as a password generator.
      fi

      ((off1--))   # Normalize. Why is this necessary?

          if [ $off1 -lt 0 ]
          then     # Catch negative indices.
            let "off1 += $wraplen"
          fi

      ((off1 %= $wraplen))   # Wrap around if past end of alphabet.

      echo -n "${alpha2[off1]}"

    done

      if [ -z "$dflag" ]
      then
        echo " $Enc_suffix"
    #   echo "$Enc_suffix"  # For password generator.
      else
        echo
      fi
    } # End encrypt/decrypt function.

    # int main () {

    # Check for command-line args.
    if [ -z "$1" ]
    then
       echo "Usage: $0 TEXT TO ENCODE/DECODE"
       exit $E_NOARGS
    fi

    if [ ${!#} == "$Enc_suffix" ]
    #    ^^^^^ Final command-line arg.
    then
      dflag=ON
      echo -n "+"           # Flag decrypted text with a "+" for easy ID.
    fi

    if [ -z "$key" ]
    then
      key="$Default_key"    # "gronsfeldk" per above.
    fi

    keylen=${#key}

    for (( idx=0; idx<$keylen; idx++ ))
    do  # Calculate shift values for encryption/decryption.
      offsets[idx]=$(expr index "${alpha1[*]}" ${key:idx:1})   # Normalize.
      ((offsets[idx]--))  #  Necessary because "expr index" starts at 1,
                          #+ whereas array count starts at 0.
      # Generate array of numerical offsets corresponding to the key.
      # There are simpler ways to accomplish this.
    done

    args=$(echo "$*" | sed -e 's/ //g' | tr A-Z a-z | sed -e 's/[0-9]//g')
    # Remove whitespace and digits from command-line args.
    # Can modify to also remove punctuation characters, if desired.

             # Debug:
             # echo "$args"; exit $DEBUG

    : "$args"               # Call the function named ":".
    # : is a null operator, except . . . when it's a function name!

    exit $?    # } End-of-script

    #   **************************************************************   #
    #   This script can function as a  password generator,
    #+  with several minor mods, see above.
    #   That would allow an easy-to-remember password, even the word
    #+ "password" itself, which encrypts to vrgfotvo29379
    #+  a fairly secure password not susceptible to a dictionary attack.
    #   Or, you could use your own name (surely that's easy to remember!).
    #   For example, Bozo Bozeman encrypts to hfnbttdppkt29379.
    #   **************************************************************   #

To end this section, a review of the basics . . . and more.

Example A-56. Basics Reviewed

    #!/bin/bash
    # basics-reviewed.bash

    # File extension == *.bash == specific to Bash

    #   Copyright (c) Michael S. Zick, 2003; All rights reserved.
    #   License: Use in any form, for any purpose.
    #   Revision: $ID$
    #
    #              Edited for layout by M.C.
    #   (author of the "Advanced Bash Scripting Guide")
    #   Fixes and updates (04/08) by Cliff Bamford.

    #  This script tested under Bash versions 2.04, 2.05a and 2.05b.
    #  It may not work with earlier versions.
    #  This demonstration script generates one --intentional--
    #+ "command not found" error message. See line 436.

    #  The current Bash maintainer, Chet Ramey, has fixed the items noted
    #+ for later versions of Bash.

            ###-------------------------------------------###
            ###  Pipe the output of this script to 'more' ###
            ###+ else it will scroll off the page.        ###
            ###                                           ###
            ###  You may also redirect its output         ###
            ###+ to a file for examination.               ###
            ###-------------------------------------------###

    #  Most of the following points are described at length in
    #+ the text of the foregoing "Advanced Bash Scripting Guide."
    #  This demonstration script is mostly just a reorganized presentation.
    #      -- msz

    # Variables are not typed unless otherwise specified.

    #  Variables are named. Names must contain a non-digit.
    #  File descriptor names (as in, for example: 2>&1)
    #+ contain ONLY digits.

    # Parameters and Bash array elements are numbered.
    # (Parameters are very similar to Bash arrays.)

    # A variable name may be undefined (null reference).
    unset VarNull

    # A variable name may be defined but empty (null contents).
    VarEmpty=''                         # Two, adjacent, single quotes.

    # A variable name may be defined and non-empty.
    VarSomething='Literal'

    # A variable may contain:
    #   * A whole number as a signed 32-bit (or larger) integer
    #   * A string
    # A variable may also be an array.

    #  A string may contain embedded blanks and may be treated
    #+ as if it where a function name with optional arguments.

    #  The names of variables and the names of functions
    #+ are in different namespaces.

    #  A variable may be defined as a Bash array either explicitly or
    #+ implicitly by the syntax of the assignment statement.
    #  Explicit:
    declare -a ArrayVar

    # The echo command is a builtin.
    echo $VarSomething

    # The printf command is a builtin.
    # Translate %s as: String-Format
    printf %s $VarSomething         # No linebreak specified, none output.
    echo                            # Default, only linebreak output.

    # The Bash parser word breaks on whitespace.
    # Whitespace, or the lack of it is significant.
    # (This holds true in general; there are, of course, exceptions.)

    # Translate the DOLLAR_SIGN character as: Content-Of.

    # Extended-Syntax way of writing Content-Of:
    echo ${VarSomething}

    #  The ${ ... } Extended-Syntax allows more than just the variable
    #+ name to be specified.
    #  In general, $VarSomething can always be written as: ${VarSomething}.

    # Call this script with arguments to see the following in action.

    #  Outside of double-quotes, the special characters @ and *
    #+ specify identical behavior.
    #  May be pronounced as: All-Elements-Of.

    #  Without specification of a name, they refer to the
    #+ pre-defined parameter Bash-Array.

    # Glob-Pattern references
    echo $*                         # All parameters to script or function
    echo ${*}                       # Same

    # Bash disables filename expansion for Glob-Patterns.
    # Only character matching is active.

    # All-Elements-Of references
    echo $@                         # Same as above
    echo ${@}                       # Same as above

    #  Within double-quotes, the behavior of Glob-Pattern references
    #+ depends on the setting of IFS (Input Field Separator).
    #  Within double-quotes, All-Elements-Of references behave the same.

    #  Specifying only the name of a variable holding a string refers
    #+ to all elements (characters) of a string.

    #  To specify an element (character) of a string,
    #+ the Extended-Syntax reference notation (see below) MAY be used.

    #  Specifying only the name of a Bash array references
    #+ the subscript zero element,
    #+ NOT the FIRST DEFINED nor the FIRST WITH CONTENTS element.

    #  Additional qualification is needed to reference other elements,
    #+ which means that the reference MUST be written in Extended-Syntax.
    #  The general form is: ${name[subscript]}.

    #  The string forms may also be used: ${name:subscript}
    #+ for Bash-Arrays when referencing the subscript zero element.

    # Bash-Arrays are implemented internally as linked lists,
    #+ not as a fixed area of storage as in some programming languages.

    #   Characteristics of Bash arrays (Bash-Arrays):
    #   --------------------------------------------

    #   If not otherwise specified, Bash-Array subscripts begin with
    #+  subscript number zero. Literally: [0]
    #   This is called zero-based indexing.
    ###
    #   If not otherwise specified, Bash-Arrays are subscript packed
    #+  (sequential subscripts without subscript gaps).
    ###
    #   Negative subscripts are not allowed.
    ###
    #   Elements of a Bash-Array need not all be of the same type.
    ###
    #   Elements of a Bash-Array may be undefined (null reference).
    #       That is, a Bash-Array may be "subscript sparse."
    ###
    #   Elements of a Bash-Array may be defined and empty (null contents).
    ###
    #   Elements of a Bash-Array may contain:
    #     * A whole number as a signed 32-bit (or larger) integer
    #     * A string
    #     * A string formated so that it appears to be a function name
    #     + with optional arguments
    ###
    #   Defined elements of a Bash-Array may be undefined (unset).
    #       That is, a subscript packed Bash-Array may be changed
    #   +   into a subscript sparse Bash-Array.
    ###
    #   Elements may be added to a Bash-Array by defining an element
    #+  not previously defined.
    ###
    # For these reasons, I have been calling them "Bash-Arrays".
    # I'll return to the generic term "array" from now on.
    #     -- msz

    echo "========================================================="

    #  Lines 202 - 334 supplied by Cliff Bamford. (Thanks!)
    #  Demo --- Interaction with Arrays, quoting, IFS, echo, * and @   ---
    #+ all affect how things work

    ArrayVar[0]='zero'                    # 0 normal
    ArrayVar[1]=one                       # 1 unquoted literal
    ArrayVar[2]='two'                     # 2 normal
    ArrayVar[3]='three'                   # 3 normal
    ArrayVar[4]='I am four'               # 4 normal with spaces
    ArrayVar[5]='five'                    # 5 normal
    unset ArrayVar[6]                     # 6 undefined
    ArrayValue[7]='seven'                 # 7 normal
    ArrayValue[8]=''                      # 8 defined but empty
    ArrayValue[9]='nine'                  # 9 normal

    echo '--- Here is the array we are using for this test'
    echo
    echo "ArrayVar[0]='zero'             # 0 normal"
    echo "ArrayVar[1]=one                # 1 unquoted literal"
    echo "ArrayVar[2]='two'              # 2 normal"
    echo "ArrayVar[3]='three'            # 3 normal"
    echo "ArrayVar[4]='I am four'        # 4 normal with spaces"
    echo "ArrayVar[5]='five'             # 5 normal"
    echo "unset ArrayVar[6]              # 6 undefined"
    echo "ArrayValue[7]='seven'          # 7 normal"
    echo "ArrayValue[8]=''               # 8 defined but empty"
    echo "ArrayValue[9]='nine'           # 9 normal"
    echo

    echo
    echo '---Case0: No double-quotes, Default IFS of space,tab,newline ---'
    IFS=$'\x20'$'\x09'$'\x0A'            # In exactly this order.
    echo 'Here is: printf %q {${ArrayVar[*]}'
    printf %q ${ArrayVar[*]}
    echo
    echo 'Here is: printf %q {${ArrayVar[@]}'
    printf %q ${ArrayVar[@]}
    echo
    echo 'Here is: echo ${ArrayVar[*]}'
    echo  ${ArrayVar[@]}
    echo 'Here is: echo {${ArrayVar[@]}'
    echo ${ArrayVar[@]}

    echo
    echo '---Case1: Within double-quotes - Default IFS of space-tab-
    newline ---'
    IFS=$'\x20'$'\x09'$'\x0A'	    #  These three bytes,
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---Case2: Within double-quotes - IFS is q'
    IFS='q'
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---Case3: Within double-quotes - IFS is ^'
    IFS='^'
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---Case4: Within double-quotes - IFS is ^ followed by
    space,tab,newline'
    IFS=$'^'$'\x20'$'\x09'$'\x0A'       # ^ + space tab newline
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---Case6: Within double-quotes - IFS set and empty '
    IFS=''
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---Case7: Within double-quotes - IFS is unset'
    unset IFS
    echo 'Here is: printf %q "{${ArrayVar[*]}"'
    printf %q "${ArrayVar[*]}"
    echo
    echo 'Here is: printf %q "{${ArrayVar[@]}"'
    printf %q "${ArrayVar[@]}"
    echo
    echo 'Here is: echo "${ArrayVar[*]}"'
    echo  "${ArrayVar[@]}"
    echo 'Here is: echo "{${ArrayVar[@]}"'
    echo "${ArrayVar[@]}"

    echo
    echo '---End of Cases---'
    echo "========================================================="; echo

    # Put IFS back to the default.
    # Default is exactly these three bytes.
    IFS=$'\x20'$'\x09'$'\x0A'           # In exactly this order.

    # Interpretation of the above outputs:
    #   A Glob-Pattern is I/O; the setting of IFS matters.
    ###
    #   An All-Elements-Of does not consider IFS settings.
    ###
    #   Note the different output using the echo command and the
    #+  quoted format operator of the printf command.

    #  Recall:
    #   Parameters are similar to arrays and have the similar behaviors.
    ###
    #  The above examples demonstrate the possible variations.
    #  To retain the shape of a sparse array, additional script
    #+ programming is required.
    ###
    #  The source code of Bash has a routine to output the
    #+ [subscript]=value   array assignment format.
    #  As of version 2.05b, that routine is not used,
    #+ but that might change in future releases.

    # The length of a string, measured in non-null elements (characters):
    echo
    echo '- - Non-quoted references - -'
    echo 'Non-Null character count: '${#VarSomething}' characters.'

    # test='Lit'$'\x00''eral'           # $'\x00' is a null character.
    # echo ${#test}                     # See that?

    #  The length of an array, measured in defined elements,
    #+ including null content elements.
    echo
    echo 'Defined content count: '${#ArrayVar[@]}' elements.'
    # That is NOT the maximum subscript (4).
    # That is NOT the range of the subscripts (1 . . 4 inclusive).
    # It IS the length of the linked list.
    ###
    #  Both the maximum subscript and the range of the subscripts may
    #+ be found with additional script programming.

    # The length of a string, measured in non-null elements (characters):
    echo
    echo '- - Quoted, Glob-Pattern references - -'
    echo 'Non-Null character count: '"${#VarSomething}"' characters.'

    #  The length of an array, measured in defined elements,
    #+ including null-content elements.
    echo
    echo 'Defined element count: '"${#ArrayVar[*]}"' elements.'

    #  Interpretation: Substitution does not effect the ${# ... } operation.
    #  Suggestion:
    #  Always use the All-Elements-Of character
    #+ if that is what is intended (independence from IFS).

    #  Define a simple function.
    #  I include an underscore in the name
    #+ to make it distinctive in the examples below.
    ###
    #  Bash separates variable names and function names
    #+ in different namespaces.
    #  The Mark-One eyeball isn't that advanced.
    ###
    _simple() {
        echo -n 'SimpleFunc'$@          #  Newlines are swallowed in
    }                                   #+ result returned in any case.

    # The ( ... ) notation invokes a command or function.
    # The $( ... ) notation is pronounced: Result-Of.

    # Invoke the function _simple
    echo
    echo '- - Output of function _simple - -'
    _simple                             # Try passing arguments.
    echo
    # or
    (_simple)                           # Try passing arguments.
    echo

    echo '- Is there a variable of that name? -'
    echo $_simple not defined           # No variable by that name.

    # Invoke the result of function _simple (Error msg intended)

    ###
    $(_simple)                          # Gives an error message:
    #                          line 436: SimpleFunc: command not found
    #                          ---------------------------------------

    echo
    ###

    #  The first word of the result of function _simple
    #+ is neither a valid Bash command nor the name of a defined function.
    ###
    # This demonstrates that the output of _simple is subject to evaluation.
    ###
    # Interpretation:
    #   A function can be used to generate in-line Bash commands.

    # A simple function where the first word of result IS a bash command:
    ###
    _print() {
        echo -n 'printf %q '$@
    }

    echo '- - Outputs of function _print - -'
    _print parm1 parm2                  # An Output NOT A Command.
    echo

    $(_print parm1 parm2)               #  Executes: printf %q parm1 parm2
                                        #  See above IFS examples for the
                                        #+ various possibilities.
    echo

    $(_print $VarSomething)             # The predictable result.
    echo

    # Function variables
    # ------------------

    echo
    echo '- - Function variables - -'
    # A variable may represent a signed integer, a string or an array.
    # A string may be used like a function name with optional arguments.

    # set -vx                           #  Enable if desired
    declare -f funcVar                  #+ in namespace of functions

    funcVar=_print                      # Contains name of function.
    $funcVar parm1                      # Same as _print at this point.
    echo

    funcVar=$(_print )                  # Contains result of function.
    $funcVar                            # No input, No output.
    $funcVar $VarSomething              # The predictable result.
    echo

    funcVar=$(_print $VarSomething)     #  $VarSomething replaced HERE.
    $funcVar                            #  The expansion is part of the
    echo                                #+ variable contents.

    funcVar="$(_print $VarSomething)"   #  $VarSomething replaced HERE.
    $funcVar                            #  The expansion is part of the
    echo                                #+ variable contents.

    #  The difference between the unquoted and the double-quoted versions
    #+ above can be seen in the "protect_literal.sh" example.
    #  The first case above is processed as two, unquoted, Bash-Words.
    #  The second case above is processed as one, quoted, Bash-Word.

    # Delayed replacement
    # -------------------

    echo
    echo '- - Delayed replacement - -'
    funcVar="$(_print '$VarSomething')" # No replacement, single Bash-Word.
    eval $funcVar                       # $VarSomething replaced HERE.
    echo

    VarSomething='NewThing'
    eval $funcVar                       # $VarSomething replaced HERE.
    echo

    # Restore the original setting trashed above.
    VarSomething=Literal

    #  There are a pair of functions demonstrated in the
    #+ "protect_literal.sh" and "unprotect_literal.sh" examples.
    #  These are general purpose functions for delayed replacement literals
    #+ containing variables.

    # REVIEW:
    # ------

    #  A string can be considered a Classic-Array of elements (characters).
    #  A string operation applies to all elements (characters) of the string
    #+ (in concept, anyway).
    ###
    #  The notation: ${array_name[@]} represents all elements of the
    #+ Bash-Array: array_name.
    ###
    #  The Extended-Syntax string operations can be applied to all
    #+ elements of an array.
    ###
    #  This may be thought of as a For-Each operation on a vector of strings.
    ###
    #  Parameters are similar to an array.
    #  The initialization of a parameter array for a script
    #+ and a parameter array for a function only differ
    #+ in the initialization of ${0}, which never changes its setting.
    ###
    #  Subscript zero of the script's parameter array contains
    #+ the name of the script.
    ###
    #  Subscript zero of a function's parameter array DOES NOT contain
    #+ the name of the function.
    #  The name of the current function is accessed by the $FUNCNAME variable.
    ###
    #  A quick, review list follows (quick, not short).

    echo
    echo '- - Test (but not change) - -'
    echo '- null reference -'
    echo -n ${VarNull-'NotSet'}' '          # NotSet
    echo ${VarNull}                         # NewLine only
    echo -n ${VarNull:-'NotSet'}' '         # NotSet
    echo ${VarNull}                         # Newline only

    echo '- null contents -'
    echo -n ${VarEmpty-'Empty'}' '          # Only the space
    echo ${VarEmpty}                        # Newline only
    echo -n ${VarEmpty:-'Empty'}' '         # Empty
    echo ${VarEmpty}                        # Newline only

    echo '- contents -'
    echo ${VarSomething-'Content'}          # Literal
    echo ${VarSomething:-'Content'}         # Literal

    echo '- Sparse Array -'
    echo ${ArrayVar[@]-'not set'}

    # ASCII-Art time
    # State     Y==yes, N==no
    #           -       :-
    # Unset     Y       Y       ${# ... } == 0
    # Empty     N       Y       ${# ... } == 0
    # Contents  N       N       ${# ... } > 0

    #  Either the first and/or the second part of the tests
    #+ may be a command or a function invocation string.
    echo
    echo '- - Test 1 for undefined - -'
    declare -i t
    _decT() {
        t=$t-1
    }

    # Null reference, set: t == -1
    t=${#VarNull}                           # Results in zero.
    ${VarNull- _decT }                      # Function executes, t now -1.
    echo $t

    # Null contents, set: t == 0
    t=${#VarEmpty}                          # Results in zero.
    ${VarEmpty- _decT }                     # _decT function NOT executed.
    echo $t

    # Contents, set: t == number of non-null characters
    VarSomething='_simple'                  # Set to valid function name.
    t=${#VarSomething}                      # non-zero length
    ${VarSomething- _decT }                 # Function _simple executed.
    echo $t                                 # Note the Append-To action.

    # Exercise: clean up that example.
    unset t
    unset _decT
    VarSomething=Literal

    echo
    echo '- - Test and Change - -'
    echo '- Assignment if null reference -'
    echo -n ${VarNull='NotSet'}' '          # NotSet NotSet
    echo ${VarNull}
    unset VarNull

    echo '- Assignment if null reference -'
    echo -n ${VarNull:='NotSet'}' '         # NotSet NotSet
    echo ${VarNull}
    unset VarNull

    echo '- No assignment if null contents -'
    echo -n ${VarEmpty='Empty'}' '          # Space only
    echo ${VarEmpty}
    VarEmpty=''

    echo '- Assignment if null contents -'
    echo -n ${VarEmpty:='Empty'}' '         # Empty Empty
    echo ${VarEmpty}
    VarEmpty=''

    echo '- No change if already has contents -'
    echo ${VarSomething='Content'}          # Literal
    echo ${VarSomething:='Content'}         # Literal

    # "Subscript sparse" Bash-Arrays
    ###
    #  Bash-Arrays are subscript packed, beginning with
    #+ subscript zero unless otherwise specified.
    ###
    #  The initialization of ArrayVar was one way
    #+ to "otherwise specify".  Here is the other way:
    ###
    echo
    declare -a ArraySparse
    ArraySparse=( [1]=one [2]='' [4]='four' )
    # [0]=null reference, [2]=null content, [3]=null reference

    echo '- - Array-Sparse List - -'
    # Within double-quotes, default IFS, Glob-Pattern

    IFS=$'\x20'$'\x09'$'\x0A'
    printf %q "${ArraySparse[*]}"
    echo

    #  Note that the output does not distinguish between "null content"
    #+ and "null reference".
    #  Both print as escaped whitespace.
    ###
    #  Note also that the output does NOT contain escaped whitespace
    #+ for the "null reference(s)" prior to the first defined element.
    ###
    # This behavior of 2.04, 2.05a and 2.05b has been reported
    #+ and may change in a future version of Bash.

    #  To output a sparse array and maintain the [subscript]=value
    #+ relationship without change requires a bit of programming.
    #  One possible code fragment:
    ###
    # local l=${#ArraySparse[@]}        # Count of defined elements
    # local f=0                         # Count of found subscripts
    # local i=0                         # Subscript to test
    (                                   # Anonymous in-line function
        for (( l=${#ArraySparse[@]}, f = 0, i = 0 ; f < l ; i++ ))
        do
            # 'if defined then...'
            ${ArraySparse[$i]+ eval echo '\ ['$i']='${ArraySparse[$i]} ; (( f++ )) }
        done
    )

    # The reader coming upon the above code fragment cold
    #+ might want to review "command lists" and "multiple commands on a line"
    #+ in the text of the foregoing "Advanced Bash Scripting Guide."
    ###
    #  Note:
    #  The "read -a array_name" version of the "read" command
    #+ begins filling array_name at subscript zero.
    #  ArraySparse does not define a value at subscript zero.
    ###
    #  The user needing to read/write a sparse array to either
    #+ external storage or a communications socket must invent
    #+ a read/write code pair suitable for their purpose.
    ###
    # Exercise: clean it up.

    unset ArraySparse

    echo
    echo '- - Conditional alternate (But not change)- -'
    echo '- No alternate if null reference -'
    echo -n ${VarNull+'NotSet'}' '
    echo ${VarNull}
    unset VarNull

    echo '- No alternate if null reference -'
    echo -n ${VarNull:+'NotSet'}' '
    echo ${VarNull}
    unset VarNull

    echo '- Alternate if null contents -'
    echo -n ${VarEmpty+'Empty'}' '              # Empty
    echo ${VarEmpty}
    VarEmpty=''

    echo '- No alternate if null contents -'
    echo -n ${VarEmpty:+'Empty'}' '             # Space only
    echo ${VarEmpty}
    VarEmpty=''

    echo '- Alternate if already has contents -'

    # Alternate literal
    echo -n ${VarSomething+'Content'}' '        # Content Literal
    echo ${VarSomething}

    # Invoke function
    echo -n ${VarSomething:+ $(_simple) }' '    # SimpleFunc Literal
    echo ${VarSomething}
    echo

    echo '- - Sparse Array - -'
    echo ${ArrayVar[@]+'Empty'}                 # An array of 'Empty'(ies)
    echo

    echo '- - Test 2 for undefined - -'

    declare -i t
    _incT() {
        t=$t+1
    }

    #  Note:
    #  This is the same test used in the sparse array
    #+ listing code fragment.

    # Null reference, set: t == -1
    t=${#VarNull}-1                     # Results in minus-one.
    ${VarNull+ _incT }                  # Does not execute.
    echo $t' Null reference'

    # Null contents, set: t == 0
    t=${#VarEmpty}-1                    # Results in minus-one.
    ${VarEmpty+ _incT }                 # Executes.
    echo $t'  Null content'

    # Contents, set: t == (number of non-null characters)
    t=${#VarSomething}-1                # non-null length minus-one
    ${VarSomething+ _incT }             # Executes.
    echo $t'  Contents'

    # Exercise: clean up that example.
    unset t
    unset _incT

    # ${name?err_msg} ${name:?err_msg}
    #  These follow the same rules but always exit afterwards
    #+ if an action is specified following the question mark.
    #  The action following the question mark may be a literal
    #+ or a function result.
    ###
    #  ${name?} ${name:?} are test-only, the return can be tested.

    # Element operations
    # ------------------

    echo
    echo '- - Trailing sub-element selection - -'

    #  Strings, Arrays and Positional parameters

    #  Call this script with multiple arguments
    #+ to see the parameter selections.

    echo '- All -'
    echo ${VarSomething:0}              # all non-null characters
    echo ${ArrayVar[@]:0}               # all elements with content
    echo ${@:0}                         # all parameters with content;
                                        # ignoring parameter[0]

    echo
    echo '- All after -'
    echo ${VarSomething:1}              # all non-null after character[0]
    echo ${ArrayVar[@]:1}               # all after element[0] with content
    echo ${@:2}                         # all after param[1] with content

    echo
    echo '- Range after -'
    echo ${VarSomething:4:3}            # ral
                                        # Three characters after
                                        # character[3]

    echo '- Sparse array gotch -'
    echo ${ArrayVar[@]:1:2}     #  four - The only element with content.
                                #  Two elements after (if that many exist).
                                #  the FIRST WITH CONTENTS
                                #+ (the FIRST WITH  CONTENTS is being
                                #+ considered as if it
                                #+ were subscript zero).
    #  Executed as if Bash considers ONLY array elements with CONTENT
    #  printf %q "${ArrayVar[@]:0:3}"    # Try this one

    #  In versions 2.04, 2.05a and 2.05b,
    #+ Bash does not handle sparse arrays as expected using this notation.
    #
    #  The current Bash maintainer, Chet Ramey, has corrected this.

    echo '- Non-sparse array -'
    echo ${@:2:2}               # Two parameters following parameter[1]

    # New victims for string vector examples:
    stringZ=abcABC123ABCabc
    arrayZ=( abcabc ABCABC 123123 ABCABC abcabc )
    sparseZ=( [1]='abcabc' [3]='ABCABC' [4]='' [5]='123123' )

    echo
    echo ' - - Victim string - -'$stringZ'- - '
    echo ' - - Victim array - -'${arrayZ[@]}'- - '
    echo ' - - Sparse array - -'${sparseZ[@]}'- - '
    echo ' - [0]==null ref, [2]==null ref, [4]==null content - '
    echo ' - [1]=abcabc [3]=ABCABC [5]=123123 - '
    echo ' - non-null-reference count: '${#sparseZ[@]}' elements'

    echo
    echo '- - Prefix sub-element removal - -'
    echo '- - Glob-Pattern match must include the first character. - -'
    echo '- - Glob-Pattern may be a literal or a function result. - -'
    echo

    # Function returning a simple, Literal, Glob-Pattern
    _abc() {
        echo -n 'abc'
    }

    echo '- Shortest prefix -'
    echo ${stringZ#123}                 # Unchanged (not a prefix).
    echo ${stringZ#$(_abc)}             # ABC123ABCabc
    echo ${arrayZ[@]#abc}               # Applied to each element.

    # echo ${sparseZ[@]#abc}            # Version-2.05b core dumps.
    # Has since been fixed by Chet Ramey.

    # The -it would be nice- First-Subscript-Of
    # echo ${#sparseZ[@]#*}             # This is NOT valid Bash.

    echo
    echo '- Longest prefix -'
    echo ${stringZ##1*3}                # Unchanged (not a prefix)
    echo ${stringZ##a*C}                # abc
    echo ${arrayZ[@]##a*c}              # ABCABC 123123 ABCABC

    # echo ${sparseZ[@]##a*c}           # Version-2.05b core dumps.
    # Has since been fixed by Chet Ramey.

    echo
    echo '- - Suffix sub-element removal - -'
    echo '- - Glob-Pattern match must include the last character. - -'
    echo '- - Glob-Pattern may be a literal or a function result. - -'
    echo
    echo '- Shortest suffix -'
    echo ${stringZ%1*3}                 # Unchanged (not a suffix).
    echo ${stringZ%$(_abc)}             # abcABC123ABC
    echo ${arrayZ[@]%abc}               # Applied to each element.

    # echo ${sparseZ[@]%abc}            # Version-2.05b core dumps.
    # Has since been fixed by Chet Ramey.

    # The -it would be nice- Last-Subscript-Of
    # echo ${#sparseZ[@]%*}             # This is NOT valid Bash.

    echo
    echo '- Longest suffix -'
    echo ${stringZ%%1*3}                # Unchanged (not a suffix)
    echo ${stringZ%%b*c}                # a
    echo ${arrayZ[@]%%b*c}              # a ABCABC 123123 ABCABC a

    # echo ${sparseZ[@]%%b*c}           # Version-2.05b core dumps.
    # Has since been fixed by Chet Ramey.

    echo
    echo '- - Sub-element replacement - -'
    echo '- - Sub-element at any location in string. - -'
    echo '- - First specification is a Glob-Pattern - -'
    echo '- - Glob-Pattern may be a literal or Glob-Pattern function result. - -'
    echo '- - Second specification may be a literal or function result. - -'
    echo '- - Second specification may be unspecified. Pronounce that'
    echo '    as: Replace-With-Nothing (Delete) - -'
    echo

    # Function returning a simple, Literal, Glob-Pattern
    _123() {
        echo -n '123'
    }

    echo '- Replace first occurrence -'
    echo ${stringZ/$(_123)/999}         # Changed (123 is a component).
    echo ${stringZ/ABC/xyz}             # xyzABC123ABCabc
    echo ${arrayZ[@]/ABC/xyz}           # Applied to each element.
    echo ${sparseZ[@]/ABC/xyz}          # Works as expected.

    echo
    echo '- Delete first occurrence -'
    echo ${stringZ/$(_123)/}
    echo ${stringZ/ABC/}
    echo ${arrayZ[@]/ABC/}
    echo ${sparseZ[@]/ABC/}

    #  The replacement need not be a literal,
    #+ since the result of a function invocation is allowed.
    #  This is general to all forms of replacement.
    echo
    echo '- Replace first occurrence with Result-Of -'
    echo ${stringZ/$(_123)/$(_simple)}  # Works as expected.
    echo ${arrayZ[@]/ca/$(_simple)}     # Applied to each element.
    echo ${sparseZ[@]/ca/$(_simple)}    # Works as expected.

    echo
    echo '- Replace all occurrences -'
    echo ${stringZ//[b2]/X}             # X-out b's and 2's
    echo ${stringZ//abc/xyz}            # xyzABC123ABCxyz
    echo ${arrayZ[@]//abc/xyz}          # Applied to each element.
    echo ${sparseZ[@]//abc/xyz}         # Works as expected.

    echo
    echo '- Delete all occurrences -'
    echo ${stringZ//[b2]/}
    echo ${stringZ//abc/}
    echo ${arrayZ[@]//abc/}
    echo ${sparseZ[@]//abc/}

    echo
    echo '- - Prefix sub-element replacement - -'
    echo '- - Match must include the first character. - -'
    echo

    echo '- Replace prefix occurrences -'
    echo ${stringZ/#[b2]/X}             # Unchanged (neither is a prefix).
    echo ${stringZ/#$(_abc)/XYZ}        # XYZABC123ABCabc
    echo ${arrayZ[@]/#abc/XYZ}          # Applied to each element.
    echo ${sparseZ[@]/#abc/XYZ}         # Works as expected.

    echo
    echo '- Delete prefix occurrences -'
    echo ${stringZ/#[b2]/}
    echo ${stringZ/#$(_abc)/}
    echo ${arrayZ[@]/#abc/}
    echo ${sparseZ[@]/#abc/}

    echo
    echo '- - Suffix sub-element replacement - -'
    echo '- - Match must include the last character. - -'
    echo

    echo '- Replace suffix occurrences -'
    echo ${stringZ/%[b2]/X}             # Unchanged (neither is a suffix).
    echo ${stringZ/%$(_abc)/XYZ}        # abcABC123ABCXYZ
    echo ${arrayZ[@]/%abc/XYZ}          # Applied to each element.
    echo ${sparseZ[@]/%abc/XYZ}         # Works as expected.

    echo
    echo '- Delete suffix occurrences -'
    echo ${stringZ/%[b2]/}
    echo ${stringZ/%$(_abc)/}
    echo ${arrayZ[@]/%abc/}
    echo ${sparseZ[@]/%abc/}

    echo
    echo '- - Special cases of null Glob-Pattern - -'
    echo

    echo '- Prefix all -'
    # null substring pattern means 'prefix'
    echo ${stringZ/#/NEW}               # NEWabcABC123ABCabc
    echo ${arrayZ[@]/#/NEW}             # Applied to each element.
    echo ${sparseZ[@]/#/NEW}            # Applied to null-content also.
                                        # That seems reasonable.

    echo
    echo '- Suffix all -'
    # null substring pattern means 'suffix'
    echo ${stringZ/%/NEW}               # abcABC123ABCabcNEW
    echo ${arrayZ[@]/%/NEW}             # Applied to each element.
    echo ${sparseZ[@]/%/NEW}            # Applied to null-content also.
                                        # That seems reasonable.

    echo
    echo '- - Special case For-Each Glob-Pattern - -'
    echo '- - - - This is a nice-to-have dream - - - -'
    echo

    _GenFunc() {
        echo -n ${0}                    # Illustration only.
        # Actually, that would be an arbitrary computation.
    }

    # All occurrences, matching the AnyThing pattern.
    # Currently //*/ does not match null-content nor null-reference.
    # /#/ and /%/ does match null-content but not null-reference.
    echo ${sparseZ[@]//*/$(_GenFunc)}

    #  A possible syntax would be to make
    #+ the parameter notation used within this construct mean:
    #   ${1} - The full element
    #   ${2} - The prefix, if any, to the matched sub-element
    #   ${3} - The matched sub-element
    #   ${4} - The suffix, if any, to the matched sub-element
    #
    # echo ${sparseZ[@]//*/$(_GenFunc ${3})}   # Same as ${1} here.
    # Perhaps it will be implemented in a future version of Bash.

    exit 0

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