Shell Programming and Scripting

Consider the following loop.
This allows three command line options , one of which accepts an argument(b),
because "b" is followed by a ":" in the getopts arguments.
When processing option b , $OPTARG holds the argument to this option.

while getopts "ab:c" opt; do
case $opt in
a ) process option -a ;;
b ) process option -b
$OPTARG is the option's argument ;;
c ) process option -c ;;

esac
done

The following while statement loops through all the options and sets them to the corresponding variable. getopts returns true while there are options to be processed. The argument string, here “hw:e:u:m:d”, specifies which options the script accepts. If the user specifies an option which is not in this string, it sets $optionName to ?. If the option is succeeded by a colon, the value immediately following the option is placed in the variable $OPTARG.

while getopts "hw:e:u:m:d" optionName; do
case "$optionName" in
h) printHelpAndExit 0;;
d) debug="0";;
w) whatTowatch="$OPTARG";;
e) email="$OPTARG";;
u) startAtUid="$OPTARG";;
m) maxCpuUsage="$OPTARG";;
[?]) printErrorHelpAndExit "$badOptionHelp";;
esac
done