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For some reason, no matter how many variations I've tried, I can't seem to execute a bash script I've written. The command words 100% fine in Terminal, but when I try calling it with a subprocess, it returns nothing.

from os import listdir
import subprocess

computer_name = 'homedirectoryname'

moviefolder = '/Users/{}/Documents/Programming/Voicer/Movies'.format(computer_name)

string = 'The lion king'

for i in listdir(moviefolder):
    title = i.split('.')
    formatted_title = title[0].replace(' ', '\ ')

    if string.lower() == title[0].lower():
        command = 'vlc {}/{}.{}'.format(moviefolder, formatted_title, title[1])

        subprocess.call(["/usr/local/bin",'-i','-c', command], stdout=subprocess.PIPE,
                                                        stderr=subprocess.PIPE, shell=True)
    else:
        continue

The bash executable file looks like this:

#/bin/bash

func() {
    open -a /Applications/VLC.app/Contents/MacOS/VLC $1
}

Where have I gone wrong?

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7
  • Not sure of the issue, but subprocess.call document says not to use PIPE with stdout and stderr Commented Jan 7, 2018 at 19:54
  • @MoinuddinQuadri If I take those out, it returns -i: /usr/local/bin: is a directory in Terminal Commented Jan 7, 2018 at 19:58
  • Why do you even try to invoke a shell? A shell is a utility that sits on top of the OS and gives you a UI to start programs. You don't need that, just start VLC. Commented Jan 7, 2018 at 20:01
  • use check_call, so you can see if your call succeeds. call doesn't check anything. Commented Jan 7, 2018 at 20:05
  • The error message is correct: /usr/local/bin is a directory. You're not expected to be able to run it as a command. Commented Jan 7, 2018 at 20:09

5 Answers 5

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2

You should call open directly:

import os
import subprocess

computer_name = 'homedirectoryname'

moviefolder = '/Users/{}/Documents/Programming/Voicer/Movies'.format(computer_name)

string = 'The lion king'

for filename in os.listdir(moviefolder):
    title = filename.split('.')

    if string.lower() == title[0].lower():
        subprocess.call(['open', '-a', '/Applications/VLC.app/Contents/MacOS/VLC', os.path.join(moviefolder, filename)])
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1 Comment

Wow. I don't know why I didn't think of this. Duh. I've used this as my solution. Thanks!
1

Since you are using shell=True, the command must be a string:

On Unix with shell=True, the shell defaults to /bin/sh. If args is a string, the string specifies the command to execute through the shell. This means that the string must be formatted exactly as it would be when typed at the shell prompt. This includes, for example, quoting or backslash escaping filenames with spaces in them. If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional arguments to the shell itself. (docs)

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6 Comments

One absolutely can pass an array with shell=True -- the first element of that array should be a script, and subsequent elements arguments to that script. It's much better practice security-wise to call subprocess.Popen(['script involving "$1", '_', python_variable]) than to do something like subprocess.Popen(['script involving %s' % (python_variable,)]).
@CharlesDuffy that's strange, because the cited docs say specifically that additional items are interpreted as args to the shell and not to the "script"
You can read the implementation if you have any question here -- shell=True literally just prepends ['sh', '-c'] to the argument list (being a single-item list with a string if a string is passed, or the literal list given by the user otherwise).
...and when sh -c '...script here...' 'argument 0' 'argument 1' 'argument 2' is run, your subsequent arguments are $0, $1, $2, etc. in the context of the script passed immediately after the -c. (Meaning if that script doesn't refer to its subsequent arguments, they're utterly ignored).
...so, yes, subsequent items are passed as arguments to the shell, but the shell passes them as arguments to the script.
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1

Like you even mentioned in a comment, you get /usr/local/bin: is a directory when you properly capture the error from the shell (and take out the erroneous shell=True; or correspondingly refactor the command line to be suitable for this usage, i.e. pass a string instead of a list).

Just to spell this out, you are attempting to run the command /usr/local/bin with some options; but of course, it's not a valid command; so this fails.

The actual script you seem to want to run will declare a function and then exit, which results in the function's definition being lost again, because the subprocess which ran the shell in which this function declaration was executed has now terminated and released all its resources back to the system.

Perhaps you should take more than just a few steps back and explain what you actually want to accomplish; but really, that should be a new, separate question.

Assuming you are actually trying to run vlc, and guessing some other things, too, perhaps you actually want

subprocess.call(['vlc','{}/{}.{}'.format(moviefolder, formatted_title, title[1]),
    stdout=subprocess.PIPE, stderr=subprocess.PIPE)

If your PATH is correct, you should not need to specify /usr/local/bin/ explicitly (and if your PATH is wrong, correct it in the code before, instead of hardcoding a directory for the executable you want to call).

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Comments

0

/usr/local/bin is a directory. You can't run a directory as if it were a command.

Anyhow, there's no point to having /usr/local/bin anywhere in your command at all. Leave out the shell=True, and explicitly call vlc:

subprocess.call([
  'vlc',
  '{}/{}.{}'.format(moviefolder, formatted_title, title[1])
])
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Comments

0

When shell=True is used in subprocess.call, if the command arguments is a sequence, then the first element of the sequence needs to be the command, and the rest are treated as argument(s) to the shell itself.

So, this should do:

subprocess.call(["/usr/local/bin/{}".format(command), '-i','-c'], shell=True, ...)

Otherwise, you can make the command a string.

Example:

In [20]: subprocess.call(["cat spamegg", "-i", "-c"], shell=True)
foobar
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4 Comments

Tried this, but it didn't work. Returned nothing. command = 'vlc {}/{}.{}'.format(moviefolder, formatted_title, title[1]) subprocess.call(["/usr/local/bin/{}".format(command), '-i','-c'], shell=True)
@AntonioNogueras What did you expect? Why are you running vlc like this? Try cvlc then. Also, try with other command.
This is still wrong because the argument to vlc should be a separate string in the command list, or the code should be refactored to use shell=True and a single command string intead.
Thanks; this rhymes well with Charles' comments to another answer on this page, though it must be regarded as undocumented behavior which could well change in a future version.

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