#!/usr/bin/perl -wT
use strict;

my @a    = 1..5;
my $l    = 3;
local $" = ',';

my @combos = grep!$;{"@$_"}++,map[sortsplit','],
             grep!/([^,]+).*,\1,/,glob"{@a},"x$l;

print "@$_\n" for @combos;

__END__
1,2,3
1,2,4
1,2,5
1,3,4
1,3,5
1,4,5
2,3,4
2,3,5
2,4,5
3,4,5