Passing double quote shell commands in python to subprocess.Popen()?

Question

I've been trying to pass a command that works only with literal double quotes in the commandline around the "concat:file1|file2" argument for ffmpeg.

I cant however make this work from python with subprocess.Popen(). Anyone have an idea how one passes quotes into subprocess.Popen?

Here is the code:

command = "ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4"  output,error = subprocess.Popen(command, universal_newlines=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate() 

When I do this, ffmpeg won't take it any other way other than quotes around the concat segement. Is there a way to successfully pass this line to subprocess.Popen command?

Answer 1

I'd suggest using the list form of invocation rather than the quoted string version:

command = ["ffmpeg", "-i", "concat:1.ts|2.ts", "-vcodec", "copy",            "-acodec", "copy", "temp.mp4"] output,error  = subprocess.Popen(                     command, universal_newlines=True,                     stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate() 

This more accurately represents the exact set of parameters that are going to be passed to the end process and eliminates the need to mess around with shell quoting.

That said, if you absolutely want to use the plain string version, just use different quotes (and shell=True):

command = 'ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4' output,error  = subprocess.Popen(                     command, universal_newlines=True, shell=True,                     stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate() 

Answer 2

Either use single quotes 'around the "whole pattern"' to automatically escape the doubles or explicitly "escape the \"double quotes\"". Your problem has nothing to do with Popen as such.

Just for the record, I had a problem particularly with a list-based command passed to Popen that would not preserve proper double quotes around a glob pattern (i.e. what was suggested in the accepted answer) under Windows. Joining the list into a string with ' '.join(cmd) before passing it to Popen solved the problem.