# `pipes` --- Interface to shell pipelines

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.

示例:

    >>> 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 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.