#!/bin/bash
# ex33.sh: Exercising getopts and OPTIND
#          Script modified 10/09/03 at the suggestion of Bill Gradwohl.


# Here we observe how 'getopts' processes command-line arguments to script.
# The arguments are parsed as "options" (flags) and associated arguments.

# Try invoking this script with:
#   'scriptname -mn'
#   'scriptname -oq qOption' (qOption can be some arbitrary string.)
#   'scriptname -qXXX -r'
#
#   'scriptname -qr'
#+      - Unexpected result, takes "r" as the argument to option "q"
#   'scriptname -q -r' 
#+      - Unexpected result, same as above
#   'scriptname -mnop -mnop'  - Unexpected result
#   (OPTIND is unreliable at stating where an option came from.)
#
#  If an option expects an argument ("flag:"), then it will grab
#+ whatever is next on the command-line.

NO_ARGS=0 
E_OPTERROR=85

if [ $# -eq "$NO_ARGS" ]    # Script invoked with no command-line args?
then
  echo "Usage: `basename $0` options (-mnopqrs)"
  exit $E_OPTERROR          # Exit and explain usage.
                            # Usage: scriptname -options
                            # Note: dash (-) necessary
fi  


while getopts ":mnopq:rs" Option
do
  case $Option in
    m     ) echo "Scenario #1: option -m-   [OPTIND=${OPTIND}]";;
    n | o ) echo "Scenario #2: option -$Option-   [OPTIND=${OPTIND}]";;
    p     ) echo "Scenario #3: option -p-   [OPTIND=${OPTIND}]";;
    q     ) echo "Scenario #4: option -q-\
                  with argument \"$OPTARG\"   [OPTIND=${OPTIND}]";;
    #  Note that option 'q' must have an associated argument,
    #+ otherwise it falls through to the default.
    r | s ) echo "Scenario #5: option -$Option-";;
    *     ) echo "Unimplemented option chosen.";;   # Default.
  esac
done

shift $(($OPTIND - 1))
#  Decrements the argument pointer so it points to next argument.
#  $1 now references the first non-option item supplied on the command-line
#+ if one exists.

exit $?

#   As Bill Gradwohl states,
#  "The getopts mechanism allows one to specify:  scriptname -mnop -mnop
#+  but there is no reliable way to differentiate what came
#+ from where by using OPTIND."
#  There are, however, workarounds.