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Anchor(faq35)

How can I handle command-line arguments to my script easily?

Well, that depends a great deal on what you want to do with them. Here's a general template that might help for the simple cases:

    # Bash
    while [[ $1 == -* ]]; do
        case "$1" in
          -h|--help|-\?) show_help; exit 0;;
          -v) verbose=1; shift;;
          -f) output_file=$2; shift 2;;
          --) shift; break;;
          -*) echo "invalid option: $1"; show_help;exit 1;;
        esac
    done

Now all of the remaining arguments are the filenames which followed the optional switches. You can process those with for i or "$@".

For more complex/generalized cases, or if you want things like "-xvf" to be handled as three separate flags, you can use getopts. (NEVER use getopt(1)!)

Here is a simplistic getopts example:

    # POSIX
    x=1         # Avoids an error if we get no options at all.
    while getopts "abcf:g:h:" opt; do
      case "$opt" in
        a) echo "You said a";;
        b) echo "You said b";;
        c) echo "You said c";;
        f) echo "You said f, with argument $OPTARG";;
        g) echo "You said g, with argument $OPTARG";;
        h) echo "You said h, with argument $OPTARG";;
      esac
      x=$OPTIND
    done
    shift $(($x-1))
    echo "Left overs: $@"

If your prefer to check options with if statements, then a function like this one may be useful:

# Bash
HaveOpt() {
  local needle=$1
  shift
  while [[ $1 == -* ]]; do
    case "$1" in
      --) return 1; # by convention, -- is end of options
      $needle) return 0;;
    esac
    shift
  done
  return 1
}
if HaveOpt --quick "$@"; then echo "Option quick is set"; fi

and it will work if script is run as:

  • YES: ./script --quick
  • YES: ./script -other --quick

but will stop on first argument with no "-" in front (or on --):

  • NO: ./script -bar foo --quick
  • NO: ./script -bar -- --quick

Of course, this approach (iterating over the argument list every time you want to check for one) is far less efficient than just iterating once and setting flag variables.

BashFAQ/035 (last edited 2024-02-26 07:51:38 by larryv)