Prev: FAQ 8.13 How do I trap control characters/signals?
Next: FAQ 5.21 How can I lock a file?
From: PerlFAQ Server on 2 Jul 2010 06:00
This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

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;



--------------------------------------------------------------------

The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.
 | 
Pages: 1
Prev: FAQ 8.13 How do I trap control characters/signals?
Next: FAQ 5.21 How can I lock a file?