AC Power script for shell scripting

ac-check.bash

#!/usr/bin/env bash

set -e

function usage() {
cat << EOF
    $0 - Returns exit code 1 when on battery power

    Backup is only run when on AC power (see --no-ac-check option).
    Example usage: "$0 && backup.sh" in cron job

    USAGE:
        -h|--help       help
        -q              quiet, no message
        --no-ac-check   disables AC power check (i.e. does nothing)

    ENV:
        NO_AC_CHECK=1   same as --no-ac-check
EOF
}

### AC Power check, can be overrwritten by the NO_AC_CHECK variable
function ac_check () {
    if [[ "${NO_AC_CHECK}" -ne 1 && $(cat /sys/class/power_supply/AC/online) -eq 0 ]] ; then
        test "${QUIET}" != "1" && echo "W: Skipped due to battery check"
        exit 1
    else
        exit 0
    fi
}

### Command line processing
for i in "$@"
do
case $i in
    -h|--help)
        shift
        usage
        exit 2
    ;;
    --no-ac-check)
        NO_AC_CHECK=1
        shift
    ;;
    -q)
        QUIET=1
        shift
    ;;
    *)
        echo "Unknown Option ${i}"
        echo "Use $0 -h for usage"
        exit 3
        # unknown option
    ;;
esac
done

### Run default commands
ac_check