Perl used to the main choice for GUPPS, but is was a collection of 
hacks. The current version uses Python and it is designed with modularity
and more professionalism. Soon, Perl will be developed in a fashion
after Python, and then PHP will be developed. So for now, Perl is disabled
by default because you shouldn't use hack software. If you actually
try to run it, it won't work because GUPPS's structure has been changed
to reflect modularity and other good things.