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How do I change the Nth occurrence of something?

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How do I change the Nth occurrence of something?

You have to keep track. For example, let's say you want to change the fifth occurrence of ``whoever'' or ``whomever'' into ``whosoever'' or ``whomsoever'', case insensitively.

    $count = 0;
    s{((whom?)ever)}{
        ++$count == 5           # is it the 5th?
            ? "${2}soever"      # yes, swap
            : $1                # renege and leave it there
    }igex;

Source: Perl FAQ: Data Manipulation
Copyright: Copyright (c) 1997 Tom Christiansen and Nathan Torkington.

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