Parse --flag=value Arguments

verbose=0
output="out.txt"
dry_run=0

while [[ $# -gt 0 ]]; do
    case "$1" in
        -v|--verbose)         verbose=1; shift ;;
        -o|--output)          output="$2"; shift 2 ;;
        --output=*)           output="${1#*=}"; shift ;;
        -n|--dry-run)         dry_run=1; shift ;;
        -h|--help)            echo "usage: ..."; exit 0 ;;
        --)                   shift; break ;;            # stop flag parsing
        -*)                   echo "Unknown flag: $1" >&2; exit 2 ;;
        *)                    args+=("$1"); shift ;;
    esac
done

echo "verbose=$verbose output=$output dry_run=$dry_run positional=${args[*]:-}"

# Call as:
#   ./script.sh -v --output=foo.txt input1 input2
#   ./script.sh --dry-run -o foo.txt input1