#!/usr/bin/perl -w
use strict;

use Getopt::Std;

my %opts;
my $usage = "usage: options [-a arga] [-b] mandatory_arg";

die "$usage \n" if !getopts("a:b", \%opts);
die "error: arguments=".@ARGV." @ARGV\n$usage \n" if @ARGV !=1;
print "ok\n";

__END__ 
# Wrong, "mandatory" used as -a's argument!
C:\TEMP>option.pl -a  mandatory
error: arguments=0
usage: options [-a arga] [-b] mandatory_arg

# Now ok!
C:\TEMP>option -a arga mandatory
ok

# Error: b doesn't take an arg
# looks like another mandatory arg!
C:\TEMP>option -a -b arga mandatory
error: arguments=2 arga mandatory
usage: options [-a arga] [-b] mandatory_arg

# -b doesn't expect an arg and that causes
# error
C:\TEMP>option.pl -b extra -a arga  mandatory
error: arguments=4 extra -a arga mandatory
usage: options [-a arga] [-b] mandatory_arg

# Now ok!
C:\TEMP>option.pl -b  -a arga  mandatory
ok