How to pass a value to shell script from subprocess.Popen in Python

Question

I have the following:

myscript.py

#!/usr/bin/python
from threading import Thread
import time
import subprocess

subprocess.Popen("./hello.sh 1", shell=True)
subprocess.Popen("./hello.sh 2", shell=True)
subprocess.Popen("./hello.sh 3", shell=True)

hello.sh

echo "Hello From Shell Script $1"

The output is:

Hello From Shell Script 1
Hello From Shell Script 2
Hello From Shell Script 3

I want to do this in a for loop like so:

for num in range(1,3):
    subprocess.Popen(['./hello.sh', str(num)], shell=True)

But the output is:

Hello From Shell Script
Hello From Shell Script
Hello From Shell Script

If I drop the shell=True so its now:

subprocess.Popen(['./hello.sh', str(num)])

I get the following:

Traceback (most recent call last):
  File "./myscript.py", line 12, in <module>
    subprocess.Popen(['./hello.sh', str(num)])
  File "/usr/lib64/python2.6/subprocess.py", line 623, in __init__
    errread, errwrite)
  File "/usr/lib64/python2.6/subprocess.py", line 1141, in _execute_child
    raise child_exception
OSError: [Errno 8] Exec format error

How can I get this to pass in the correct value to the script?

Since you are passing list of arguments, simply drop shell=True keyword argument. — Łukasz Rogalski
– Łukasz Rogalski, Commented Feb 9, 2016 at 15:20

Rolf of Saxony · Accepted Answer · 2016-02-09 15:29:52Z

1

Change it to read as follows:

>>> for num in range(1,3):
...     subprocess.Popen(['./hello.sh '+str(num)], shell=True)

answered Feb 9, 2016 at 15:29

Rolf of Saxony

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2 Comments

chepner Over a year ago

There's no reason to pass a list to Popen if it only contains one string.

Rolf of Saxony Over a year ago

@chepner Is it a list?

chepner · Accepted Answer · 2016-02-09 15:34:04Z

1

Don't use shell=True if you are passing a list instead of a string as the first argument.

subprocess.Popen(['./hello.sh', str(num)])

answered Feb 9, 2016 at 15:34

chepner

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3 Comments

Rolf of Saxony Over a year ago

Isn't shell=True required for "./hello.sh"?

chepner Over a year ago

Not necessarily. If the script is executable, execve will execute the script with /bin/sh (or whatever its shebang specifies). Specifying shell=True is just a shortcut for ["/bin/sh", "-c"] + arglist. (Where arglist is either the list you pass, or a single-element list containing the string you passed.)

rici Over a year ago

I'd say just "Don't use shell=True". Period.

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