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Output Redirection and Pipes
============================
As in POSIX shells, output of a command can be redirected and/or piped. This
feature is fully cross-platform and works identically on Windows, macOS, and
Linux.
Output Redirection
------------------
Redirect to a file
~~~~~~~~~~~~~~~~~~
Redirecting the output of a ``cmd2`` command to a file works just like in
POSIX shells:
- send to a file with ``>``, as in ``mycommand args > filename.txt``
- append to a file with ``>>``, as in ``mycommand args >> filename.txt``
If you need to include any of these redirection characters in your command, you
can enclose them in quotation marks, ``mycommand 'with > in the argument'``.
Redirect to the clipboard
~~~~~~~~~~~~~~~~~~~~~~~~~
``cmd2`` output redirection supports an additional feature not found in most
shells - if the file name following the ``>`` or ``>>`` is left blank, then
the output is redirected to the operating system clipboard so that it can
then be pasted into another program.
- overwrite the clipboard with ``mycommand args >``
- append to the clipboard with ``mycommand args >>``
Pipes
-----
Piping the output of a ``cmd2`` command to a shell command works just like in
POSIX shells:
- pipe as input to a shell command with ``|``, as in ``mycommand args | wc``
Multiple Pipes and Redirection
------------------------------
Multiple pipes, optionally followed by a redirect, are supported. Thus, it is
possible to do something like the following::
(Cmd) help | grep py | wc > output.txt
The above runs the **help** command, pipes its output to **grep** searching for
any lines containing *py*, then pipes the output of grep to the **wc**
"word count" command, and finally writes redirects the output of that to a file
called *output.txt*.
Disabling Redirection
---------------------
.. note::
If you wish to disable cmd2's output redirection and pipes features, you can
do so by setting the ``allow_redirection`` attribute of your ``cmd2.Cmd``
class instance to ``False``. This would be useful, for example, if you want
to restrict the ability for an end user to write to disk or interact with
shell commands for security reasons::
from cmd2 import Cmd
class App(Cmd):
def __init__(self):
super().__init__(allow_redirection=False)
cmd2's parser will still treat the ``>``, ``>>``, and `|` symbols as output
redirection and pipe symbols and will strip arguments after them from the
command line arguments accordingly. But output from a command will not be
redirected to a file or piped to a shell command.
Limitations of Redirection
--------------------------
Some limitations apply to redirection and piping within ``cmd2`` applications:
- Can only pipe to shell commands, not other ``cmd2`` application commands
- **stdout** gets redirected/piped, **stderr** does not
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