#!/usr/bin/perl -w
use strict;
while(<DATA>){
        chomp;
   next unless /^([^\|]+)/;
   print "$1\n";
}
__DATA__
category1
category1|subcat1
category1|subcat1|subcat1
category1|subcat1|subcat2
category1|subcat1|subcat3
category1|subcat2
category1|subcat2|subcat1
category2

##</code><code>##

-- 
Joost       downtime n. The period during which a system
            is error-free and immune from user input.