You can do this:

no warnings ;
no warnings 'all' ;

You can use the chdir function from Perl. Maybe the cd command doesn't change the current working directory. You can check it with the getcwd function from Perl.
...

Use regular expressions. Here is the link:

http://www.troubleshooters.com/codecorn/littperl/perlreg.htm

You can use Getopt. Here is the link:

http://perldoc.perl.org/Getopt/Long.html