When assembling regular expressions, beware: if $delimiter had any regex special characters, you would have to use \Q$delimiter\E in the assembled regex. 
my $delimiter = '.';
my $nth = 3;
my $regex = '^(' .
            ('.*\Q' . $delimiter . '\E') x $nth .
            ')';

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In reply to Re^2: Replacing nth occurrence of string by halley
in thread Replacing nth occurrence of string by loris

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