output the command line called by subprocess?

Question

I’m using the subprocess.Popen call, and in another question I found out that I had been misunderstanding how Python was generating arguments for the command line.

My Question
Is there a way to find out what the actual command line was?

Example Code :-

proc = subprocess.popen(....)
print "the commandline is %s" % proc.getCommandLine()

How would you write getCommandLine ?

Asked By: Brian Postow

||

Source

Answer 1

It depends on the version of Python you are using. In Python3.3, the arg is saved in proc.args:

proc = subprocess.Popen(....)
print("the commandline is {}".format(proc.args))

In Python2.7, the args not saved, it is just passed on to other functions like _execute_child. So, in that case, the best way to get the command line is to save it when you have it:

proc = subprocess.Popen(shlex.split(cmd))
print "the commandline is %s" % cmd

Note that if you have the list of arguments (such as the type of thing returned by shlex.split(cmd), then you can recover the command-line string, cmd using the undocumented function subprocess.list2cmdline:

In [14]: import subprocess

In [15]: import shlex

In [16]: cmd = 'foo -a -b --bar baz'

In [17]: shlex.split(cmd)
Out[17]: ['foo', '-a', '-b', '--bar', 'baz']

In [18]: subprocess.list2cmdline(['foo', '-a', '-b', '--bar', 'baz'])
Out[19]: 'foo -a -b --bar baz'

Answered By: unutbu

Answer 2

The correct answer to my question is actually that there IS no command line. The point of subprocess is that it does everything through IPC. The list2cmdline does as close as can be expected, but in reality the best thing to do is look at the “args” list, and just know that that will be argv in the called program.

Answered By: Brian Postow

Answer 3

Beautiful and scalable method

I have been using something like this:

#!/usr/bin/env python3

import os
import shlex
import subprocess
import sys

def run_cmd(cmd, cwd=None, extra_env=None, extra_paths=None, dry_run=False):
    if extra_env is None:
        extra_env = {}
    newline_separator = ' \n'
    out = []
    kwargs = {}
    env = os.environ.copy()

    # cwd
    if 'cwd' is not None:
        kwargs['cwd'] = cwd

    # extra_env
    env.update(extra_env)
    for key in extra_env:
        out.append('{}={}'.format(shlex.quote(key), shlex.quote(extra_env[key])) + newline_separator)

    # extra_paths
    if extra_paths is not None:
        path = ':'.join(extra_paths)
        if 'PATH' in env:
            path += ':' + env['PATH']
        env['PATH'] = path
        out.append('PATH="{}:${{PATH}}"'.format(':'.join(extra_paths)) + newline_separator)

    # Command itself.
    for arg in cmd:
        out.append(shlex.quote(arg) + newline_separator)

    # Print and run.
    kwargs['env'] = env
    print('+ ' + '  '.join(out) + ';')
    if not dry_run:
        subprocess.check_call(cmd, **kwargs)

run_cmd(
    sys.argv[1:],
    cwd='/bin',
    extra_env={'ASDF': 'QW ER'},
    extra_paths=['/some/path1', '/some/path2']
)

Sample run:

./a.py echo 'a b' 'c d'

Output:

+ ASDF='QW ER' 
  PATH="/some/path1:/some/path2:${PATH}" 
  echo 
  'a b' 
  'c d' 
;
a b c d

Feature summary:

makes huge command lines readable with one option per line
add a + to commands like sh -x so users can differentiate commands from their output easily
show cd, and extra environment variables if they are given to the command. These only printed if given, generating a minimal shell command.

All of this allows users to easily copy the commands manually to run them if something fails, or to see what is going on.

Tested on Python 3.5.2, Ubuntu 16.04. GitHub upstream.

Answered By: Ciro Santilli OurBigBook.com

Answer 4

You can see it by passing the process id to ps command, if you are on POSIX OS:

import subprocess

proc = subprocess.Popen(["ls", "-la"])
subprocess.Popen(["ps", "-p", str(proc.pid)])

Output (see the CMD column):

  PID TTY           TIME CMD
 7778 ttys004    0:00.01 ls -la

Answered By: catwith

Answer 5

On windows, I used @catwith ‘s trick (thanks, btw):

wmic process where "name like '%mycmd%'" get processid,commandline

where "mycmd" is a part of the cmd unique to your command (used to filter irrelevant system commands)

That’s how I revealed another bug in the suprocess vs windows saga. One of the arguments I had had its double-quotes escaped a-la unix! "asdasd"

Answered By: Berry Tsakala

output the command line called by subprocess?

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