#! /bin/bash

_get() {
    sudo ddcutil getvcp 10 | grep -o ' current value = \+[0-9]\+' | awk '{print $4}'
}

_set() {
    sudo ddcutil setvcp 10 "$1"
}

args="$*"

case "$args" in
    '') _get;;
    *)
        if [[ "$args" =~ ^[0-9]+$ && "$args" -gt -1 && "$args" -lt 101 ]]; then
            _set "$args"
        else
            printf 'Error: expected a numeric argument between 0 and 100, but given "%s"\n' "$args" >&2
            exit 1
        fi
esac