#!/usr/bin/perl
use strict;no strict 'refs';use warnings;use re 'eval';

	my $num =3;
	$"='.*?';"@{ [1..12] }" =~ /@{[ ('\b(\d+)\b')x $num]}(?{{print ((join "_",map {$$_}1..$num),"\n")}})(?!)/;
__END__
1_2_3
1_2_4
1_2_5
1_2_6
1_2_7
...
8_11_12
9_10_11
9_10_12
9_11_12
10_11_12