#!/bin/bash
## Illustrates getopts.

usage()
{       ## ${0##*/} is a builtin equivalent to $( basename $0 )
	echo >&2 Usage: $( basename $0 ) \
		'{-a|-b} [-cCde] [-o outfile] [-t type] file [file...]'
	exit 1
}

## Make some variables local so that they are initialized to null.
typeset flag_ab flag_cC flag_d flag_e flag_t arg_t outputfile
## Alternately use seven lines like
#  flag_ab=


while getopts abcCdeo:t: opt
do
    case $opt in
	a)	if [ "$flag_ab" != "" ] ; then usage ; else
			flag_ab=a_seen 
		fi ;;
	b)	if [ "$flag_ab" != "" ] ; then usage ; else
			flag_ab=b_seen 
		fi ;;
	c|C)	flag_cC=set ;;
	d)	flag_d=set ;;
	e)	flag_e=set ;;
	o)      outputfile="$OPTARG" ;;
	t)      flag_t=set
		arg_t="$OPTARG" ;;
    ## The next two patterns show how to override the default messages.
    ## To use, put an initial colon on the getopts string like this:
    ##    while getopts :abcCdeo:t: opt
    ##
        \?)      echo >&2 Unknown option: -"$OPTARG"
		usage ;;
        :)      echo >&2 Option -"$OPTARG" requires argument
		usage ;;
    ## If you don't use the two patterns above then just do this instead:
	*)      usage ;;
    esac
done
## At this point OPTIND will be position of next argument (the first operand).
shift $(( OPTIND - 1 ))      ## Shift off all options and arguments.

if [[ "$flag_ab" = "" ]] ; then 
	echo >&2 Must select one of -a or -b
        usage
fi

if [[ $# = 0 ]] ; then 
	echo >&2 Need a file operand
	usage
fi

## Done with option processing.  Body goes below.

echo "Flags:       $flag_ab flag_cC=$flag_cC flag_d=$flag_d flag_e=$flag_e"
echo "Outputfile:  $outputfile"
echo "Flag_t:      $flag_t  $arg_t"
echo "Files:       $*"