use 5.010;  # needs (?(?{ CODE })yes-pattern) regex extension

use strict;
use warnings;

use Cwd;

my $marker = '.marker';

cwd =~ m{
    \A (.*) (?: / | \z)
    # (??{ print "at level '$1' \n";  ! -f "$1/$marker"})
    (?(?{ print "at level '$1' \n";  ! -f "$1/$marker" }) (*FAIL))
    }xms
    or die "'$marker' not found";

print "found '$marker' in '$1' \n";