# Tar

From GNU's Tar Page:

  "The `Tar` program provides the ability to create tar archives, as well as various other kinds of manipulation. For example, you can use Tar on previously created archives to extract files, to store additional files, or to update or list files which were already stored."

As an early Unix compression format, `tar` files (known as tarballs) are widely used for packaging in Unix-like operating systems. Both pacman and AUR packages are tarballs, and Arch uses GNU's `Tar` program by default.

## Usage

For `tar` archives, `Tar` by default will extract the file according to its extension:

    $ tar xvf file.EXTENSION

Forcing a given format:

File Type | Extraction Command
--- | ---
`file.tar` | `tar xvf file.tar`
`file.tgz` | `tar xvzf file.tgz`
`file.tar.gz` | `tar xvzf file.tar.gz`
`file.tar.bz` | `bzip -cd file.bz | tar xvf -`
`file.tar.bz2` | `tar xvjf file.tar.bz2` `bzip2 -cd file.bz2 | tar xvf -`
`file.tar.xz` | `tar xvJf file.tar.xz` `xz -cd file.xz | tar xvf -`

The construction of some of these `Tar` arguments may be considered legacy, but they are still useful when performing specific operations. The Compatibility section of `Tar`'s man page shows how they work in detail.

### As a cp alternative

Copying a directory tree and its contents to another filesystem using

    $ cp -pR directory /target

is not always sufficient.

Using `Tar` instead will preserve ownership, permissions, and timestamps.

This neat trick allows using `Tar` to perform a recursive copy without creating an intermediate `tar` file and overcoming all `cp` shortcomings.

To copy all of the files and subdirectories in the current working directory to the directory `/target`, use:

    $ tar cf - * | ( cd /target; tar xfp -)

The first part of the command before the pipe instructs `Tar` to create an archive of everything in the current directory and write it to standard output (the `-` in place of a filename frequently indicates stdout). The commands within parentheses cause the shell to change directory to the target directory and untar data from standard input. Since the `cd` and `Tar` commands are contained within parentheses, their actions are performed together.

The `-p` option in the tar extraction command directs `Tar` to preserve permission and ownership information, if possible given the user executing the command. If you are running the command as root, this option is turned on by default and can be omitted.

Note that the `*` will not copy any of the files prefixed with a `.` in the root directory. It is tricky to wildcard these files because one does not want to include the `.` and `..` directories, so usually one adds `.??*` to pick up everything else except for one- and two-character filenames prefixed with the `.` (e.g. `.a`, `.bc`). To copy these as well, you will want to list them by doing:

    $ ls -a

in the root directory first and typing those explicitly.

In summary, I would recommend this instead:

    $ tar cf - * .??* | ( cd /target; tar xfp -)

but first do:

    $ ls -a

and if you see anything starting with a `.` (besides `..`) that is not followed by more then two characters, add those as well; e.g.:

    $ tar cf - * .??* .a .z .bc | ( cd /target; tar xfp -)

## See Also

- GNU tar manual (Also available via `info tar`)

Category:

- Data compression and archiving