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34.10. pipes — Interface to shell pipelines
Platforms: Unix
Source code: Lib/pipes.py
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('pipefile', 'w')
>>> f.write('hello world')
>>> f.close()
>>> open('pipefile').read()
'HELLO WORLD'
34.10.1. 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.