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How do I change the Nth occurrence of something?

Jasmine
Administrator

Jan 19, 2001, 2:50 PM

Post #1 of 1 (1221 views)

How do I change the Nth occurrence of something?	Can't Post

(From the Perl FAQ)

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.

Code

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

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

Code

    $WANT = 3; 
    $count = 0; 
    while (/(\w+)\s+fish\b/gi) { 
        if (++$count == $WANT) { 
            print "The third fish is a $1 one.\n"; 
            # Warning: don't `last' out of this loop 
        } 
    }

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

Code

    /(?:\w+\s+fish\s+){2}(\w+)\s+fish/i;

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