"Syntax error: Unterminated quoted string" error when calling a bash script from Python

Question

I have a situation where, I need to call a bash script inside a python script which is in turn called inside another python script.

download-output-files.py:

#!/usr/bin/env python
import os
import sys

for i in node_path:
    cmd="python watcher.py "+i
    os.system(cmd) ##calling another python script

watcher.py:

#!/usr/bin/env python
import os
import time

        if 'finish' in child:
            print "finish found"
        cmd="./copy_output_file.sh "+node   
        os.system(cmd) ##Calling shell script here

copy_output_file.sh:

#!/bin/bash

filepath=$1
cp ff /home/likewise-open/TALENTICA-ALL/mayankp/kazoo/$filepath

When I run download-output-files.py , it calls watcher.py , which in turn calls copy_output_file.sh and below is the error I face:

mayankp@mayankp:~/kazoo$ python download-output-files.py 

finish found
sh: 1: Syntax error: Unterminated quoted string

When I run the same commands in Python shell, it runs bash script successfully. What am I missing?

I wouldn't be surprised if it's caused by the unquoted variables in the shell script. But why are you using a shell script for something that could easily be done with Python?! — Biffen
– Biffen, Commented Apr 11, 2016 at 7:46
This seems like way too much code for this question. Will retract my close vote if you can trim it down to a minimal example. — Chris Martin
– Chris Martin, Commented Apr 11, 2016 at 7:51
@ChrisMartin, I've edited my code keeping minimal code. Could you please help now? — Mayank Porwal
– Mayank Porwal, Commented Apr 11, 2016 at 8:51
@Biffen, What do you mean when you say unquoted variables in shell script? I want to copy a file to another server, hence I wanted to use scp. In the code above, it's just a sample bash script. I have no clue how to copy a file to another server in Python. — Mayank Porwal
– Mayank Porwal, Commented Apr 11, 2016 at 8:53
@MayankPorwal filepath=$1 should be filepath="$1", etc. shellcheck.net is a great tool for checking such things. — Biffen
– Biffen, Commented Apr 11, 2016 at 9:16

Chris Martin · Accepted Answer · 2016-04-11 08:56:58Z

4

It's generally unwise to concatenate strings into shell commands. Try inserting print(cmd) before your os.system(cmd) calls to find out exactly what commands you're trying to run, and I supect you'll notice what the problem is (likely a file name with an apostrophe in it).

Try using subprocess.call(['python', 'watcher.py', i]) instead of os.system("python watcher.py "+i), and subprocess.call(['/copy_output_file.sh', node]) instead of os.system(cmd="./copy_output_file.sh "+node).

answered Apr 11, 2016 at 8:56

Chris Martin

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1 Comment

Mayank Porwal Over a year ago

I inserted a print(cmd) before os.system(cmd) and it worked. Thanks

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