This appears to work:

#!/usr/bin/perl

use strict;
use warnings;

open my $infh, '<', 'testdat.dat' or die "Cannot open 'testdat.dat' be
+cause: $!";

while ( my $line = <$infh> ) {
    if ( $line =~ /^zone\s*(\S+)\s+\S+\s*$/ ) {
        open my $outfh, '>', $1 or die "Cannot open '$1' because: $!";
        select $outfh;
        }
    print $line or die "Failed to write to file: $!";
    }

close $infh;
[download]