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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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