Traditionally, "It does not work" is a common yet very undescriptive error message. Maybe you can tell us more exactly how it does not work. For example, when approaching the issue of running an external program, I use the following code:

#!/usr/bin/perl -w
use strict;
my $program = "rnafold";
my $cmd = "$program -p -noOUTPUTFILE";
system($cmd) == 0
    or die "Couldn't launch [$cmd]: $!/$?";
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This usually gives me an informative error message about what happened. Maybe you can do the same and tell us about the error message.

As an aside, there seem to be some problems with your keyboard. Please have a technician check your CAPS Lock key and your "A" and "E" keys. They seem to become stuck or not to register at all at times.