#!/usr/bin/perl -s
if ($a) { print "user selected a\n"; }
elsif ($b) { print "user selected b\n"; }
elsif ($c) { print "user selected c\n"; }
else { print "no args!\n"; }

##</code><code>##

[larryk@home] /home/larryk > somescript -a
user selected a
[larryk@home] /home/larryk > somescript -b
user selected b
[larryk@home] /home/larryk > somescript -c
user selected c
[larryk@home] /home/larryk > somescript
no args!