#!/usr/bin/perl

# https://perlmonks.org/?node_id=1222668

use strict;
use warnings;

sub flatten { map ref($_) ? flatten(@$_) : $_, @_ }

my @groups = [ [ 23 ], [ 22 ] ];   # note, single item array :)

my $perms = join ',', flatten(@groups);
print "$perms\n";

# more complex example

@groups = ( [ 20, 21, [22, 23], 24], [ [ 25 ], [ [ [ 26 ] ] ] ], 27 );
$perms = join ',', flatten(@groups);
print "$perms\n";