#!/bin/sh

usage() {
	echo `basename $0`: ERROR: $* 1>&2
	echo usage: `basename $0` '[-[abc]] [-o file]' '[file ...]' 1>&2
	exit 1
}

set -- `getopt "abco:" "$@"` || usage

a= b= c= o= 
while :
do
        case "$1" in
        -a) a=1;;
        -b) b=1;;
        -c) c=1;;
        -o) shift; o="$1";;
        --) break;;
        esac
        shift
done
shift # get rid of --
# rest of script...