read variable value from bash executable

Question

I have a script:

x.sh:

#!/bin/bash
echo nir

config.sh:

#!/bin/bash
x=$(/home/nir/x.sh)

script.py:

#!/usr/bin/env python3
#execute config.sh and read x into y
print(y)

terminal:

$ ] ./x.sh
nir
$ ] . ./config.sh
$ ] echo $x
nir
$ ] ./script.py
nir

I want to use config.sh in a python script to execute it and then read the value in x. Not sure how to do it.

echo nir will not echo nir variable. I think you may have wanted to use echo $nir — sudden_appearance
– sudden_appearance, Commented Dec 28, 2022 at 7:52
To make it clear: In your example, you want to receive the string nir inside your Python program? — user1934428
– user1934428, Commented Dec 28, 2022 at 7:55

Walter A · Accepted Answer · 2022-12-28 12:43:36Z

1

Since config.sh is not showing output, you need another command for showing the value of x. Any shell variable set in a subprocess is lost when the subprocess is finished, so you can not use two calls to subprocess.
The same problem is valid for config.sh: the variables are lost when the script is finished. You need to source the file with a . for the variable to be remembered in the subprocess environment. Before finishing the subcommand, you must echo the value.
All steps together:

#!/usr/bin/env python3
import subprocess

cmd = '''
. /home/nir/config.sh
echo "$x"
'''

# returns output as byte string
returned_output = subprocess.check_output(cmd, shell=True)

# using decode() function to convert byte string to string
y=returned_output.decode("utf-8")
print(y)

answered Dec 28, 2022 at 12:43

Walter A

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3 Comments

Nir Over a year ago

work great! one question - how can I make the path of config.sh relative to the location of script.py? (which is the script you actual wrote)

Walter A Over a year ago

Try . ./config.sh (first dot for source, second for relative to current dir).

Nir Over a year ago

found it os.path.join(os.path.dirname(__file__),....

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