Look-ahead is (?= ), not (?: ) !

13:46 >perl -wMstrict -MData::Dump -E "my $foo = '123456789'; my @w1 =
+ ($foo =~ /(?=(\d{3}))/g); dd \@w1;"
[123, 234, 345, 456, 567, 678, 789]

13:46 >

[download]

Update: The use of (?: ) instead of (?= ) appears to be a misprint in the Camel Book.

The following explanation from that same section (page 248) is worth noting (at least, it helped me to understand what is going on):

When the engine sees that it should try again because of the /g, it steps one character past where last it tried.

This explains why the final . in BrowserUk’s solution is not strictly necessary. But BrowserUk’s regex can be usefully generalised to step forward an arbitrary number of characters. For example, to capture 3 digits and then step forward 2 characters:

17:56 >perl -wMstrict -MData::Dump -E "my $foo = '123456789012345'; my
+ @w1 = ($foo =~ /(?=(\d{3})).{2}/g); dd \@w1;"
[123, 345, 567, 789, 901, 123, 345]

18:09 >

[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: Lookahead assertion by Athanasius
in thread Lookahead assertion by talexb

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