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.

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

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:

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



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