match the nth pattern

abubacker has asked for the wisdom of the Perl Monks concerning the following question:

Dear all ,

 
1-hai 2-hai 3-hai 4-hai(this pattern needs to be matched )
[download]

I want a regular expression which is to match the 4th occurrence of hai ( in this example ),
Actually I want a method to match the nth occurrence of a pattern in a string.
can I achieve this using perl regular expression in a straight forward manner
please help me out !

Comment on match the nth pattern Download Code

Replies are listed 'Best First'.
Re: match the nth pattern by JavaFan (Canon) on Aug 18, 2009 at 10:24 UTC
There's no special syntax or functionality to do this. So you have to do it yourself. And it depends whether you want the nth non-overlapping, or the nth overlapping match. For instance, the line `"hahahaha"` has 2 non-overlapping matches of `"haha"`, but three overlapping. For non overlapping, this may work for you: `($str =~ /hai/g)[3]; # Fourth match` [download] For overlapping, try: `($str =~ /(?=(hai))/g)[3]; # Fourth match` [download]	[reply] [d/l] [select]
Re: match the nth pattern by BioLion (Curate) on Aug 18, 2009 at 10:28 UTC
What have you tried so far? A simple solution might to be match all occurrences and then select which you want to keep : `use strict; use warnings; my $string = '1potato 2potato 3potato 4 potato'; print +( $string =~ m/(\d+potato)/g )[2];` [download] Just a something something...	[reply] [d/l]