use warnings;
use strict;

my $infn = 'testdat.dat';
open(my $infh, '<', $infn) or die "$infn: $!";

my $outfh;
my $filecount = 0;
while ( my $line = <$infh> ) {
	if ( $line =~ /^zone\s+(\w+)\W+\w+\s*$/ ) {
		close $outfh if $outfh;
		my $outfn = sprintf '%s-%d.txt', $1, ++$filecount;
		open($outfh, '>', $outfn) or die "$outfn: $!";
	}
	if ($outfh) {
		print {$outfh} $line or die "print: $!";
	}
}

close($outfh) if $outfh;
close($infh);