.. include:: ../header.txt

.. _use_pipe:

Use a Pipe For That
===========================

.. centered:: The Pipe (`|`)

.. index:: pipe, |

A fundamental concept that will be used in filtering data and for the rest
of the semester is that of the **pipe**.  A pipe is a facility of the shell
that makes it very easy to chain together multiple commands.  A pipe is
called upon with the vertical bar character (**\ |**).  When used between
two Unix commands, it means that output from the first command should become
the input to the second command.  For example, to count how many files
underneath a directory have been modified in the last day, the
:command:`find` and :command:`wc` commands may be used along with a pipe
(:ref:`find`, :ref:`wc`).  The :command:`find` command will list the
modified files and :command:`wc` can count them::

    find . -type f -mtime -1 | wc -l


.. seealso:: :ref:`pipe`