.. 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:
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 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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