I have a python script a.py which is run by a shell script b.sh. I wish to return the result (which is int) of a.py to b.sh.
I know I can use sys.exit(result) in a.py. But as I wrote set -ex in b.sh, the shell script stops after running a.py. I don't wish to use print(result) eather because I wish to print other information in a.py.
Is there any other way to return result from a.py to b.sh?
I would recommend writing the integer value to a file. I completely agree that exit codes should not be used for passing any information, other than success or failure of the program.
For example b.sh:
#! /bin/bash
set -ex
# Create temp file, ensure it is erased on bash script exit
tempfile="$(mktemp)"
trap 'rm -f "$tempfile"' EXIT
trap 'exit 1' HUP INT QUIT PIPE TERM
# Run program and write value to temp file
python3 ./a.py -o "$tempfile"
# Read value from temp file
myvalue="$(cat "$tempfile")"
echo "Value from a.py was: $myvalue"
And a.py:
#! /usr/bin/env python3
import argparse
from pathlib import Path
parser = argparse.ArgumentParser()
parser.add_argument(
"-o",
"--output-file",
help="Write integer value to text file",
type=str,
required=True,
)
args = parser.parse_args()
my_value = 42
Path(args.output_file).write_text(str(my_value))
You can do something like this:
{ a.py; result=$?; } || true
# the result of a.py is in $result
|| true temporarily disables set -e, and the $? special variable gets stored to $result before it gets overwritten by the next command.
The downside is that, if your script actually fails (e.g. by raising an exception), you won't notice that. A more robust solution would be to print the needed result and catch it as output, and print the other output to the standard error.
You can return the exit code from the python script and look it up (and reassign to another variable if necessary) in the shell script via $?:
foo.py:
import sys
sys.exit(35)
foo.sh:
python foo.py
echo $?
Run the scripts:
> sh foo.sh
35
set -e.a.py||false, but what's the point in returning a certain exit code, if you don't want to evaluate it?