FAQ 4.28: How do I change the Nth occurrence of something?

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4.28: How do I change the Nth occurrence of something?

    You have to keep track of N yourself. For example, let's say you want to
    change the fifth occurrence of "whoever" or "whomever" into "whosoever"
    or "whomsoever", case insensitively. These all assume that $_ contains
    the string to be altered.

        $count = 0;
            ++$count == 5           # is it the 5th?
                ? "soever"      # yes, swap
                : $1                # renege and leave it there

    In the more general case, you can use the "/g" modifier in a "while"
    loop, keeping count of matches.

        $WANT = 3;
        $count = 0;
        $_ = "One fish two fish red fish blue fish";
        while (/(\w+)\s+fish\b/gi) {
            if (++$count == $WANT) {
                print "The third fish is a $1 one.\n";

    That prints out: "The third fish is a red one." You can also use a
    repetition count and repeated pattern like this:



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