Hi Sravani
The following takes a single argument from command line and shows an usage message upon wrong input

use Getopt::Long;

sub usage {
 print "\nUsage: thisProgram -f <expectedUserInput>\n";
 exit(1);
}

GetOptions("f=s=>\$userInput");
&usage() if (!defined($userInput));
[download]

Cheers,
Gaurav