set bash variable from python script

Question

i'm calling a python script inside my bash script and I was wondering if there is a simple way to set my bash variables within my python script.

Example:

My bash script:

#!/bin/bash
someVar=""
python3 /some/folder/pythonScript.py

My python script:

anotherVar="HelloWorld"

Is there a way I can set my someVar to the value of anotherVar? I was thinking of printing properties in a file inside the python script and then read them from my bash script but maybe there is another way. Also I don't know and don't think it makes any difference but I can name both variable with the same name (someVar/someVar instead of someVar/anotherVar)

• Hackaholic: why you wan to use bash , if python can do anything
• Melodie Gauthier: Good remark. I was thinking about doing it in python and can't remember why I changed my mind. Re-considering it thanks
• Martin Tournoij: Shell scripting is good is you call a lot of external utilities (like sort, grep, find, etc.); sometimes you can do a lot with just 2 or 3 lines of shell script, that would take maybe 20 or more lines in Python... It all depends on right tools for the right job ... That said, shell scripting is hard & full of pitfalls. It also does not scale well to larger applications. It's like a hammer: it has it's uses, but use it indiscriminately, and someone will end up crying sooner or later.

Answer 1

No, when you execute python, you start a new process, and every process has access only to their own memory. Imagine what would happen if a process could influence another processes memory! Even for parent/child processes like this, this would be a huge security problem.

You can make python print() something and use that, though:

#!/usr/bin/env python3
print('Hello!')

And in your shell script:

#!/usr/bin/env bash
someVar=$(python3 myscript.py)
echo "$someVar"

There are, of course, many others IPC techniques you could use, such as sockets, pipes, shared memory, etc... But without context, it's difficult to make a specific recommendation.

Answer 2

shlex.quote() in Python 3, or pipes.quote() in Python 2, can be used to generate code which can be evaled by the calling shell. Thus, if the following script:

#!/usr/bin/env python3
import sys, shlex
print('export foobar=%s' % (shlex.quote(sys.argv[1].upper())))

...is named setFoobar and invoked as:

eval "$(setFoobar argOne)"

...then the calling shell will have an environment variable set with the name foobar and the value argOne.