33.10. pipes — Interface to shell pipelines

Platforms: Unix

Source code: Lib/pipes.py

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The 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 /bin/sh command lines, a POSIX or compatible shell for os.system() and os.popen() is required.

The pipes module defines the following class:

class pipes.Template

An abstraction of a pipeline.

Example:

>>> import pipes
>>> t=pipes.Template()
>>> t.append('tr a-z A-Z', '--')
>>> f=t.open('/tmp/1', 'w')
>>> f.write('hello world')
>>> f.close()
>>> open('/tmp/1').read()
'HELLO WORLD'

33.10.1. Template Objects

Template objects following methods:

Template.reset()

Restore a pipeline template to its initial state.

Template.clone()

Return a new, equivalent, pipeline template.

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.

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.)

Template.prepend(cmd, kind)

Add a new action at the beginning. See append() for explanations of the arguments.

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.

Template.copy(infile, outfile)

Copy infile to outfile through the pipe.