If you're using CGI.pm, it has URI (as well as HTML) encoding and decoding included, though you have to request them by name. From Master Stein's page:

escape(), unescape()

     use CGI qw/escape unescape/;
     $q = escape('This $string contains ~wonderful~ characters');
     $u = unescape($q);

http://stein.cshl.org/WWW/software/CGI/cgi_docs.html