my %fh; # hash of filehandles
while ( <> ) {
    # do something to find out the $subcat(egory)
    # and open the file if not done already
    $fh{$subcat} || open($fh{$subcat}, ">$pathtofile"
        or die "Aaargh: $!";
    # now you can print stuff to the file
    print { $fh{$subcat} } @stuff;
}
# Close down everything
close $_ foreach values %fh;