Passing variable from python script to bash script

Question

Currently trying to pass a parameter from my python script to a bash script I created. How can I can get user input from my python script to my bash script?

This is the code for my python script 'passingParameters.py' which I used to try and send a variable (loop) to my bash script. I have tested this python script (after I adjusted the code) by sending the output to another python script which I used to read the input.

loop = str(sys.argv[1])
subprocess.check_call( ["./test.sh", loop], shell=True)

This is the code for my bash script 'test.sh'. I have tested this script by itself to confirm that it does receive user input when I just call the bash script from the command line.

echo "This number was sent from the passParameters.py script: " $1

The code should work. Do you get an error? Or why do you think the parameter isn't passed? — Aaron Digulla
– Aaron Digulla, Commented Aug 5, 2014 at 13:57
@AaronDigulla no error, just the value I input into the command line doesn't show up — Mark O'Sullivan
– Mark O'Sullivan, Commented Aug 5, 2014 at 14:27
Possible duplicate of How to pass variables from python script to bash script — jww
– jww, Commented Sep 23, 2018 at 0:34

cronos · Accepted Answer · 2014-08-05 14:10:39Z

4

If you use shell=True then the executable is /bin/sh, which then calls test.sh but never sees the loop variable. You can either set shell=False and add the #!/bin/sh to the shell script,

#! /bin/sh
echo "This number was sent from the passParameters.py script: " $1

and

subprocess.check_call( ["./test.sh", loop], shell=False)

or pass the variable as a string:

subprocess.check_call( ["./test.sh %s" % loop], shell=True)

shell=True is not recommended anyway.

answered Aug 5, 2014 at 14:10

cronos

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4 Comments

chepner Over a year ago

+1 It's not well documented, but combining your list of arguments with shell=True will result in the following command: sh -c ./test.sh <loop>. This will still run ./test.sh, but the argument loop is passed to sh as $0 rather than to ./test.sh as $1.

Mark O'Sullivan Over a year ago

Thanks for your help! This first suggestion works fine. I tried the second suggestion with shell=True and it didn't work, says invalid syntax for the % beside loop.

Mark O'Sullivan Over a year ago

@chepner that's what I thought might have explained why it wasn't displayed so instead of having $1 in the bash script, I tried $0 and it still didn't print out anything.

tripleee Over a year ago

When you pass the variable as a string, the list is just superfluous. subprocess.check_call("./test.sh %s" % loop, shell=True). But as you note, you really want to avoid shell=True if you can. See also Actual meaning of shell=True in subprocess

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