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## 4. Pipes

This section explains in a very simple and practical way how to use pipes, nd why you may want it.

## 4.1 What they are and why you'll want to use them

Pipes let you use (very simple, I insist) the output of a program as the input of another one

## 4.2 Sample: simple pipe with sed

This is very simple way to use pipes.

> `

>             ls -l | sed -e "s/[aeio]/u/g"

> `

Here, the following happens: first the command ls -l is executed, and it's output, instead of being printed, is sent (piped) to the sed program, which in turn, prints what it has to.

## 4.3 Sample: an alternative to ls -l *.txt

Probably, this is a more difficult way to do ls -l *.txt, but it is here for illustrating pipes, not for solving such listing dilema.

> `

>             ls -l | grep "\.txt$"

> `

Here, the output of the program ls -l is sent to the grep program, which, in turn, will print lines which match the regex "\.txt$".

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