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:mod:`pipes` --- Interface to shell pipelines
=============================================
.. module:: pipes
:platform: Unix
:synopsis: A Python interface to Unix shell pipelines.
.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
**Source code:** :source:`Lib/pipes.py`
--------------
The :mod:`pipes` module defines a class to abstract the concept of a *pipeline*
--- a sequence of converters from one file to another.
Because the module uses :program:`/bin/sh` command lines, a POSIX or compatible
shell for :func:`os.system` and :func:`os.popen` is required.
The :mod:`pipes` module defines the following class:
.. class:: Template()
An abstraction of a pipeline.
Example::
>>> import pipes
>>> t = pipes.Template()
>>> t.append('tr a-z A-Z', '--')
>>> f = t.open('pipefile', 'w')
>>> f.write('hello world')
>>> f.close()
>>> open('pipefile').read()
'HELLO WORLD'
.. _template-objects:
Template Objects
----------------
Template objects following methods:
.. method:: Template.reset()
Restore a pipeline template to its initial state.
.. method:: Template.clone()
Return a new, equivalent, pipeline template.
.. method:: Template.debug(flag)
If *flag* is true, turn debugging on. Otherwise, turn debugging off. When
debugging is on, commands to be executed are printed, and the shell is given
``set -x`` command to be more verbose.
.. method:: Template.append(cmd, kind)
Append a new action at the end. The *cmd* variable must be a valid bourne shell
command. The *kind* variable consists of two letters.
The first letter can be either of ``'-'`` (which means the command reads its
standard input), ``'f'`` (which means the commands reads a given file on the
command line) or ``'.'`` (which means the commands reads no input, and hence
must be first.)
Similarly, the second letter can be either of ``'-'`` (which means the command
writes to standard output), ``'f'`` (which means the command writes a file on
the command line) or ``'.'`` (which means the command does not write anything,
and hence must be last.)
.. method:: Template.prepend(cmd, kind)
Add a new action at the beginning. See :meth:`append` for explanations of the
arguments.
.. method:: Template.open(file, mode)
Return a file-like object, open to *file*, but read from or written to by the
pipeline. Note that only one of ``'r'``, ``'w'`` may be given.
.. method:: Template.copy(infile, outfile)
Copy *infile* to *outfile* through the pipe.
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