使用用户在 Python 中插入的文件运行 Linux shell 脚本

Question

I am trying to run a ffprobe command using a pre-defined by the user input file in Python. And then I will use the generated file by this command to report some parameters in a more organized view. My code is:

import subprocess
import json

cmd = "ffprobe -v quiet -print_format -show_format -show_streams /path/to/input/file.mp4 > output.json" 
subprocess.call(cmd.split())

with open('output.json') as json_data:
        data = json.load(json_data)
        json_data.close()
        d = float((data["streams"][0]["duration"]))
        t = (data["streams"][0]["time_base"])
        fps = [float(x) for x in t.split('/')]
        print "==========================General=========================="
        print "Name of the File: %s" %(data["format"]["filename"])
        print "Duration: %.2f minutes" %(d/60)
        print "Frame Rate: %d fps" %fps[1]
        print "Bitrate: %.2f Mbps" %(float(data["format"]["bit_rate"])/1000000)

I was thinking to use: input_file = ("Please enter the path to your input file: ") and then use the input_file in the ffprobe command on the second line of my code. But I am not sure how I can do it within the quotes. Please also note that the file name should also include an extension like input.mp4.

Answer 1

Shell redirection ( > ) will only work when shell=True is passed to subprocess.call() . Generally you should avoid doing that, specially if you take user input as part of the executed command, in which a case you need to make sure that the user input is properly escaped, eg by using shlex.qutoe() .

Instead of using redirection in the shell you can open the file to write in python and pass it as stdout , or if you don't need the file you can use subprocess.check_output() instead of subprocess.call() :

input_filename = raw_input("Please enter the path to your input file: ")
cmd = ['ffprobe', '-v', 'quiet', '-print_format', 'json', '-show_format', '-show_streams',
       input_filename]

returned_data = subprocess.check_output(cmd)
data = json.loads(returned_data.decode('utf-8'))    # assuming the returned data is utf-8 encoded

...

Or the same with using a file to write to:

input_filename = raw_input("Please enter the path to your input file: ")
cmd = ['ffprobe', '-v', 'quiet', '-print_format', 'json', '-show_format', '-show_streams',
       input_filename]

with open('output.json', 'wb') as outfile:
    subprocess.call(cmd, stdout=outfile)

with open('output.json', 'r') as infile:
    data = json.load(infile)

...

In this case the input filename doesn't need to be quoted because it is not interpreted by a shell.

Answer 2

This should work:

#!/usr/bin/env python
import subprocess
import json

input_file = raw_input("Please enter the input file path: ")

returned_data = subprocess.check_output(['ffprobe', '-v', 'quiet', '-print_format', 'json', '-show_format', '-show_streams', input_file])
data = json.loads(returned_data.decode('utf-8'))