Checking if subprocess call executed successfully

Question

So I am still teaching myself Python and I wanted to created a small script for my server that will tell me if my HDD is mounted and if not to mount it for me when I sign in. (I have it in ~/.bashrc).

The problem I am facing is this:

try:
    with open('/media/Hitachi/mountfile.txt', 'r') as f:
        print(f.readline())
except:
        print('HDD is not mounted')
        if not os.path.exists('/media/Hitachi/media'):
                print('Attempting to mount HDD')
                script = subprocess.call('mountscript.sh', shell=True)

How can I find out if mountscript.sh succeeded or not?

iirc subprocess.call returns the exit code.. so you could just check if script==0 ? — Gryphius
– Gryphius, Commented Nov 14, 2013 at 7:20

Taylan Aydinli · Accepted Answer · 2013-11-14 07:49:39Z

4

subprocess.call method returns the returncode of the process so you can check that to see whether the call succeeded.

>>> subprocess.call(["ls", "-l"])
0
>>> subprocess.call("exit 1", shell=True)
1

answered Nov 14, 2013 at 7:49

Taylan Aydinli

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Back2Basics · Accepted Answer · 2013-11-14 08:16:35Z

0

why not a simple if/else statement and use check_call

if os.path.exists('/media/Hitachi/mountfile.txt'):
    print("it's mounted")
else:
    print('HDD is not mounted')
    if not os.path.exists('/media/Hitachi/media'):
        print('Attempting to mount HDD')
        script = subprocess.check_call(['mountscript.sh','2>file.txt'], shell=True)

Regardless of that, the moral of the story is don't forget the brackets around the command arguments to subprocess.call() or check_call()

edited Nov 14, 2013 at 8:16

answered Nov 14, 2013 at 7:22

Back2Basics

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4 Comments

Joseph Over a year ago

Because I am trying to teach myself other methods, so even if this is less simplistic, its a learning exercise for myself.

Back2Basics Over a year ago

"The try-expect construct is only used for handling exceptions that modules can throw. It should never be used as an alternative to if-else." learnpythonthehardway.org/book/ex48.html

Joseph Over a year ago

Thank you :), by the way, is there a way to pipe unix errors that moutnscript my encounter to a text file?

glglgl Over a year ago

... which probably doesn't work as intended or ist at least bad style: if you use shell=True, you should use a string, not a list of strings. Better do with open("file.txt", "w") as f: script = subprocess.check_call(['mountscript.sh'], stderr=f)

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