Other than that you have missed the closing double quotes at the my $intro line it seems OK to me and if indeed the show param is passed to your script by the webserver it should work as expected. (tested it in the CGI-simulation mode of the Komodo-editor)
CountZero
"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law
Comment on Re^5: how to exec a CGI file with params?