#!/usr/bin/perl
use strict;use warnings;
	my $num =3;
	$"=',';print join "\n",glob join "_",("{@{ [1..12] }}")x$num;
___END___
1_1_1
1_1_2
1_1_3
1_1_4
1_1_5
1_1_6
...
12_12_7
12_12_8
12_12_9
12_12_10
12_12_11
12_12_12

##</code><code>##

#!/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

##</code><code>##

"1 2 3 4" =~ /\b(\d+)\b.*?\b(\d+)\b(?{{print "$1_$2\n"}})(?!)/;