Scripting – Piping Python Variable Value to Bash Script

pythonscripting

After years of bash scripting I've been given the task of modifying a python script to have it call a shell script when certain conditions are met. That part wasn't too bad, but now I'm trying to also send this shell script a variable from within the python script and I'm getting lost.

The shell script takes stdin, which is where I'm trying to place the value of the python variable, which is just an interger.

my code (so far) looks like this:

if VAR > NUMBER:
import os
bashCommand = "echo something | /path/to/script --args"
os.system(bashCommand)

and it works just fine. But what I am looking to do is make os.system(bashCommand) an equivalent of:

echo $VAR | /path/to/script --args

or even

echo 'some text' $VAR | /path/to/script --args

given the way os.system appears to work though it seems I'm approaching this completely wrong.

So I guess my question is how can I pass the value of VAR to bashCommand, preferably as stdin?

Best Answer

Python doesn't expand variables in strings in the same way as bash. If you have VAR in python and want to pass that to bash you could do

subprocess.call('echo {} | /path/to/script --args'.format(VAR), shell=True)

if VAR in python holds the name of a bash variable you want to expand you could do similar:

subprocess.call('echo "${}" | /path/to/script --args'.format(VAR), shell=True)
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