Actually can be easily modified to generate strings with a specified length (not just the full length):

use Data::Dumper;

use strict;
use warnings;

my @set = ('1', '2', '3', '4');
my $len = 3; #test shows that it is safe to specify len greater than s
+et size, or equal to set size, or less than
my @strings = generate($len, @set);
print Dumper(\@strings);

sub generate {
    my $len = shift;
    my @set = @_;
    my @strings;
    if ($#set == 0) {
        return ($set[0]);
    } else {
    if ($len == 1) {
        push @strings, "$_" foreach (@set);    
    } else {
            for (0 .. $#set) {
                my @temp = @set;
                my $t = splice(@temp, $_, 1);
            push @strings, "$t$_" foreach (generate($len - 1, @temp));
        }
    }
        return @strings;
    }
}
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