use strict;
my @chr = map chr, 33..126;

my @stack;
my $fresh;

while (1) {
    if (not @stack) {
        $fresh++;
    }
    else {
        shift @{$stack[-1]};
        if (not @{$stack[-1]}) {
            pop @stack;
            $fresh++;
            redo;
        }
    }

    push @stack, map [@chr], 1..$fresh;
    $fresh = 0;

    print map $_->[0], @stack;
    print "\n";
}