.. include:: ../header.txt

.. seealso:: :ref:`io`

.. _redirect:

File Redirection
===========================

.. index:: redirection, stdin, stdout, stderr, > , <, 2>&1

As was discussed in :ref:`io`, standard input, output and error (stdin, stdout,
stderr) are open file descriptors in every process.

stdin Redirection
-------------------

Redirect standard input from a file (instead of the keyboard) using the
``<`` metacharacter.

::

    $ command < file    

stdout Redirection
-------------------

Redirect standard output to a file (instead of the terminal) using the
``>`` metacharacter.  The ``>>`` metacharacter redirects stdout appending 
the file.

::

    $ command > file    

    $ command >> file    


stderr Redirection
-------------------

Redirect standard error (error messages) to a file (instead of the terminal)
using the ``2>`` metacharacter.  The ``2>&1`` metacharacter redirects stderr
to the same file that stdout was redirected to.

::

    # stdout to terminal and stderr to file:
    $ command 2> file 

    # stdout and stderr to different files:
    $ command > out_file  2> error_file   

    # stdout and stderr to the same file:
    $ command > file 2>&1