Output The Command Line Called By Subprocess?

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

Solution 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'

Solution 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.

Solution 3:

Beautiful and scalable method

I have been using something like this:

#!/usr/bin/env python3import os
import shlex
import subprocess
import sys

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

    # cwdif'cwd'isnotNone:
        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_pathsif extra_paths isnotNone:
        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) + ';')
    ifnot 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.