A stackoverflow post has a template for handling command line arguments.

Does the test [ $# == 0 ] mean that a bash script shouldn't be run without any argument? As a template, I think that scripts generally do not necessarily require any argument.

In the case statement, how different are the two cases *) and "?") ? They seem the same.

# --- Options processing -------------------------------------------

if [ $# == 0 ] ; then

    echo $USAGE

    exit 1;

fi



while getopts ":i:vh" optname

  do

    case "$optname" in

      "v")

        echo "Version $VERSION"

        exit 0;

        ;;

      "i")

        echo "-i argument: $OPTARG"

        ;;

      "h")

        echo $USAGE

        exit 0;

        ;;

      "?")

        echo "Unknown option $OPTARG"

        exit 0;

        ;;

      ":")

        echo "No argument value for option $OPTARG"

        exit 0;

        ;;

      *)

        echo "Unknown error while processing options"

        exit 0;

        ;;

    esac

  done



shift $(($OPTIND - 1))



param1=$1

param2=$2

This script requires at least one arg, if not it displays usage info. It should do echo $USAGE >&2 as this is an error. Other scripts may work with zero arguments, so you will have to modify. Just as some don't take the argument i.

"?", vs *

Yes they are different:

• 
  "?" says to case to look for a ?. This is what getopts returns when it finds an option that it does not expect (invalid option).


• 
  * says to case, do this is you find no other match. This should not happen, but it may. It probably indicates a bug in getopts, or more likely your program (see defensive programming).

They should be the same.

However that code has its own share of problems:

• failure to quote arithmetic expansions; should be shift "$(($OPTIND - 1))"
  


• usage of the unportable == operator


• error messages written to stdout


• exit with 0 (success) status in case of error


• failure to quote variables; should be "$#" and echo "$USAGE"
  


• bad placement of the if-no-arguments check; it should be after the getopts loop, in order to not be fooled by script --
  


• useless quoting of v, h, i and :i:vh