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