Something like this:

my( $serial, $name, $category ) = $filename =~ 
        /^(\d+)([A-Z][a-z]*)([A-Z][a-z]*)/;
[download]

Or if you want to use the POSIX character classes:

my( $serial, $name, $category ) = $filename =~ 
        /^(\d+)([[:upper:]][[:lower:]]*)([[:upper:]][[:lower:]]*)/;
[download]

• Updated:
  Normally I don't update my nodes, but Aristotle makes an important point below, and I'd be afraid that someone might cargo-cult my original code, which had [:lower:] instead of [[:lower:]], etc.

jdporter
The 6th Rule of Perl Club is -- There is no Rule #6.