.. include:: ../header.txt

.. _pipe_shell:
.. _pipe:

The Pipe (`|`)
===========================

.. index:: pipe, stdout, stdin, stderr, |

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

To send out from stderr to the same pipe that stdout was sent to, put ``|&``,
which is short for ``2>&1 |`` at the end of the command.

::

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