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.
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'
-
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
quotefunction in theshlexmodule.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:
-
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 -xcommand 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.