36.11. 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.
-
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'
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pipes.quote(s)
Deprecated since version 2.7: Prior to Python 2.7, this function was not publicly documented. It is
finally exposed publicly in Python 3.3 as the
quote function in the shlex module.
Return a shell-escaped version of the string s. The returned value is a
string that can safely be used as one token in a shell command line, for
cases where you cannot use a list.
This idiom would be unsafe:
>>> filename = 'somefile; rm -rf ~'
>>> command = 'ls -l {}'.format(filename)
>>> print command # executed by a shell: boom!
ls -l somefile; rm -rf ~
quote() lets you plug the security hole:
>>> command = 'ls -l {}'.format(quote(filename))
>>> print command
ls -l 'somefile; rm -rf ~'
>>> remote_command = 'ssh home {}'.format(quote(command))
>>> print remote_command
ssh home 'ls -l '"'"'somefile; rm -rf ~'"'"''
The quoting is compatible with UNIX shells and with shlex.split():
>>> remote_command = shlex.split(remote_command)
>>> remote_command
['ssh', 'home', "ls -l 'somefile; rm -rf ~'"]
>>> command = shlex.split(remote_command[-1])
>>> command
['ls', '-l', 'somefile; rm -rf ~']
36.11.1. Template Objects
Template objects following methods:
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Template.reset()
Restore a pipeline template to its initial state.
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Template.clone()
Return a new, equivalent, pipeline template.
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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.
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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.)
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Template.prepend(cmd, kind)
Add a new action at the beginning. See append() for explanations of the
arguments.
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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.
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Template.copy(infile, outfile)
Copy infile to outfile through the pipe.