Bash tips & tricks [ep. 6]: Check the exit code

This is the fifth epidose of a small series.

Description:

Every command in a script may fail due to external reasons. Bash programming is not functional programming!

After running a command, make sure that you check the exit code and either raise a warning or exit with an error, depending on how a failure can impact the execution of the script.

BAD:

The worst example is not to check the exit code at all:

#!/bin/bash -l

recover -a -f -c ${NWCLIENT} -d ${DEST_FILE_PATH} $BASEBCK_FILENAME
# what if recover fails?

do_something_with_recovered_files

Next one is better, but you may have a lot of additional code to type:

#!/bin/bash -l

recover -a -f -c ${NWCLIENT} -d ${DEST_FILE_PATH} $BASEBCK_FILENAME

#---------
# the following piece of code is frequently copied&pasted 
ERR=$?
if [ $ERR -ne 0 ] ; then
    # I've got an error with the recovery
    eerror "The recovery failed with exit code $ERR"
    Log_Close
    exit $ERR
else
    eok "The recovery succeeded."
fi
#---------

do_something_with_recovered_files

Again, Log_Close, eok, eerror, etc are functions defined using the previous Bash Tips & Tricks in this series.

GOOD:

Define once the check functions that you will use after every command:

# F_check_warn will eventually raise a warning but let the script continue
function F_check_warn() {
        EXITCODE=$1
        shift
        if [ $EXITCODE -eq 0 ] ; then
                eok $@ succeded with exit code $EXITCODE
        else
                ewarn $@ failed with exit code $EXITCODE. The script will continue.
        fi
        # return the same code so other checks can follow this one inside the script
        return $EXITCODE
}

# F_check_warn will eventually raise an error and exit
function F_check_exit() {
        EXITCODE=$1
        shift
        if [ $EXITCODE -eq 0 ] ; then
                eok $@ succeded with exit code $EXITCODE
        else
                eerror $@ failed with exit code $EXITCODE. The script will exit.
                Log_Close
                exit $EXITCODE
        fi
}

CMD="recover -a -f -c ${NWCLIENT} -d ${DEST_FILE_PATH} $BASEBCK_FILENAME"
enotify "Recover command: $CMD"
eval $CMD
F_check_exit $? "Recovery from networker"

do_something_with_the_recovered_files
F_check_warn $? "Non-blocking operation with recovered files"