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use strict;
use warnings;
...

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

c:\@Work\Perl\monks\1nickt\two\one\zero>perl find_marker_1.pl
at level 'c:/@Work/Perl/monks/1nickt/two/one/zero'
...
at level 'c:/@Work/Perl/monks/1nickt'
at level 'c:/@Work/Perl/monks'
found '.marker' in 'c:/@Work/Perl/monks'

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

...
    or die "'$marker' not found";

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

c:\@Work\Perl\monks\1nickt\two\one\zero>perl find_marker_2.pl
at level 'c:/@Work/Perl/monks/1nickt/two/one/zero'
...
at level 'c:/@Work'
at level 'c:'
'.marker' not found at find_marker_2.pl line 62.