Top left of the Perlmonks page is the search box ... search for 'debugger'. or go to CPAN and search for perldebug in the Perl core documentation, or type 'perldoc perldebug' into an xterm window, if you have access to a Unix system. Then you'll be able to see for yourself what funny characters are showing up in your strings.

You call clean_extension() with an argument, but you never use it, never even unload it from @_.