!/usr/bin/perl
use strict;
use warnings;

my @output = (
	{ file => "chr1.gens", pattern => qr/^0/ },
	{ file => "chr2.gens", pattern => qr/^1/ },
	{ file => "chr3.gens", pattern => qr/^2/ },
);

my $file = "test.txt";
open(IN,'<'.$file) || die "Can not open file $file: $!";

# open the output handles
foreach my $o (@output) {
	my $file = $o->{file};
	open(my $handle, "> $file") or die "Can't open $file: $!";
	$o->{handle} = $handle;
}

while (my $line = <IN>) {
		
	foreach my $o (@output) {
	
		my $pattern = $o->{pattern};
		if($line =~ $pattern) {
			print $o->{handle} $line;
			# oder eben print $o->{handle} "$line\n";
			# falls das zusätzlich \n erwünscht ist
		}
	}
		
}

# close the output handles
foreach my $o (@output) { close $o->{handle}; }

close IN;