Passing command line argument to subprocess module

Question

I have a Python script which calls Perl script using subprocess module. In terminal I run the Perl script like this:

perl email.pl [email protected]

I am passing in "[email protected]" as command line argument to that script. This is my Python script:

import subprocess

pipe = subprocess.Popen(["perl","./email.pl"])
print pipe

This works fine. But if I pass arguments it throws file not found:

import subprocess

pipe = subprocess.Popen(["perl","./email.pl moun"])
print pipe

Error:

<subprocess.Popen object at 0x7ff7854d6550>
Can't open perl script "./email.pl moun": No such file or directory

How can I pass command line arguments in this case?

eph · Accepted Answer · 2015-12-04 03:10:26Z

4

The command can be a string:

pipe = subprocess.Popen("perl ./email.pl moun")

or a list:

pipe = subprocess.Popen(["perl", "./email.pl", "moun"])

When it is a list, Python will escape special chars. So when you say

pipe = subprocess.Popen(["perl","./email.pl moun"])

It calls

perl "./email.pl moun"

But the file "email.pl moun" doesn't exist.

Above is a rough explanation and only works in Windows. For more detail, see @ShadowRanger 's comment.

edited Dec 4, 2015 at 3:10

answered Dec 4, 2015 at 2:38

eph

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1 Comment

ShadowRanger Over a year ago

The solution (second block of code) is correct, but the explanation is only loosely applicable to Windows systems, and wrong everywhere else. On non-Windows systems, Python isn't escaping a thing in the list based invocation (it's converting to a C level array of C-style strings and passing it directly to an execvp system call after fork). The first block of code isn't legal without passing shell=True on non-Windows systems. Even on Windows systems, the list based invocation is usually safer, because Python is better at handling the necessary escaping to produce the command string.

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