use File::Find;
@ARGV = '.' unless @ARGV;
find sub {  # all code comes here
    return unless -f;
    # $_ is basename, use this because we have chdir'ed to its directory
    if(/\.txt$/) {
       say $File::Find::name;
    }
    elsif(/\.zip$/) {
       # process ZIP file
    }
    elsif(/\.mp3$/) {
       # process mp3 file
    }
}, @ARGV;