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 ?

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'

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.