pos($str) - length($&)? Ewwww. First of all, $& is a Curse, and second, you can just use $-[0] to get the same location. 
while ($str =~ /,/g) { $p = $-[0], last if !--$nth }

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Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re^2: search for nth occurrence of a pattern in a line by japhy
in thread search for nth occurrence of a pattern in a line by deepa

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