bash EXIT traps to ensure resource cleanup

traps.bash

#!/bin/bash

# Call like `./traps.bash 0` and you should see:
#   outside
#   level 1
#   level 2
#   level 2 trap
#   This won't run on error
#   level 1 trap
#   Nor with this on error
#
# Call like `./traps.bash 1` and you should see:
#   outside
#   level 1
#   level 2
#   level 2 trap
#   level 1 trap


level1_cleanup() {
    echo "level 1 trap"
}


# You can also call a function that also sets its own trap
levelX() {
    echo level $1 
    trap "echo level $1 trap" EXIT
}


main() {
    # we are concerned about failures and need to exit
    # early, so we set -e to bail out if a problem
    set -e

    # some code on the outside
    echo "outside"
    
    # we use subshells so we can trap the exit from
    # each subshell "level" and perform a cleanup action
    (
        # some command that makes something you need to cleanup
        echo "level 1"
        trap level1_cleanup EXIT
        # code using resource
        
        (
            # another command that makes something you need to cleanup
            levelX 2
            # code using resource
            # ...
            # some command that errors and retuns an
            # exit code of whatever is passed in
            exit $1
        )
        # back out to level 1
        echo "This won't run on error"
    )
    # more code on the outside
    echo "Nor with this on error"
}


main $@

See more about exit traps here: http://redsymbol.net/articles/bash-exit-traps/.