Bash getops template

getops_tmpl.sh

usage() { echo "Usage: $0 [-s <45|90>] [-p <string>]" 1>&2; exit 1; }

while getopts ":s:p:" o "$@"; 
do
    case $o in
        s) s=${OPTARG}
            ((s == 45 || s == 90)) || usage;; 

        p)p=${OPTARG};;

        *)  usage ;;
    esac
done
shift $((OPTIND-1))

if [ -z "${s}" ] || [ -z "${p}" ]; then
    usage
fi

echo "s = ${s}"
echo "p = ${p}"

# test command: -s: check if string is empty
#               -f: check if file exist
#               -s: check not empty  
#               -ne: not equal (ex: INTEGER1 -ne INTEGER2)
#               -z: the length of STRING is zero

# 1>&2
# 1 = standard output
# 2 = standard error

# "$@" - optional positional parameters except $0    
# "$#" - the number of arguments, not counting $0
# "$2" - second positional parameter