CODEWITHSUNDEEP
bashcronexit-codesubshell
Julio María Meca Hansen
Julio María Meca Hansen

Reputation: 1268

Getting the exit code of a Python script launched in a subshell with Bash

I want to run a Bash script every minute (through a CRON entry) to launch a series of Python scripts in a granular (time-wise) fashion.

So far, this is the script I've made:

# set the current date
DATE=`date +%Y-%m-%d`

# set the current system time (HH:MM)
SYSTIME=`date +%H-%M`

# parse all .py script files in the 'daily' folder
for f in daily/*.py; do
    if [[ -f $f ]]; then
        # set the script name
        SCRIPT=$(basename $f)

        # get the script time
        SCRTIME=`echo $SCRIPT | cut -c1-5`

        # execute the script only if its intended execution time and the system time match
        if [[ $SCRTIME == $SYSTIME ]]; then
            # ensure the directory exists
            install -v -m755 -d done/$DATE/failed

            # execute the script
            python3 evaluator.py $f > done/$DATE/daily-$SCRIPT.log &

            # evaluate the result
            if [ $? -eq 0 ]; then
                # move the script to the 'done' folder
                cp $f done/$DATE/daily-$SCRIPT
            else
                # log the failure
                mv done/$DATE/daily-$SCRIPT.log done/$DATE/failed/

                # move the script to the 'retry' folder for retrial
                cp $f retry/daily-$SCRIPT
            fi
        fi
    fi
done

Let's say we have the following files in a folder called daily/ (for daily execution):

daily/08-00-script-1.py
daily/08-00-script-2.py
daily/08-05-script-3.py
daily/09-20-script-4.py

The idea for granular execution is that a CRON task runs this script every minute. I fetch the system time and extract the execution time for each script and when the time matches between the system and the script file, it gets handed over to Python. So far, so good.

I know this script is not right in the sense that it gets a subshell for each script that's going to be executed but the following code is wrong as I know Bash automatically returns 0 on subshell invocation (if I did read correctly while searching on Google) and what I need is for each subshell to execute the code below so, if it fails, it gets sent to another folder (retry/) which is controlled by another Bash script running checks every 30 minutes for retrial (it's the same script as this one minus the checking part).

So, basically, I need to run this:

# evaluate the result
if [ $? -eq 0 ]; then
    # move the script to the 'done' folder
    cp $f done/$DATE/daily-$SCRIPT
else
    # log the failure
    mv done/$DATE/daily-$SCRIPT.log done/$DATE/failed/

    # move the script to the 'retry' folder for retrial
    cp $f retry/daily-$SCRIPT
fi

For every subshell-ed execution. How can I do this the right way?

Upvotes: 0

Views: 340

Answers (1)

Paul
Paul

Reputation: 582

Bash may return 0 for every sub-shell invocation, but if you wait for the result, then you will get the result (and I see no ampersand). If the python3 commands is relaying the exit code of the script, then your code will work. If your code does not catch an error, then it is the fault of python3 and you need to create error communication. Redirecting the output of stderr might be helpful, but first verify that your code does not work.

Upvotes: 1

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