I've been tinkering around with regular expressions, and in particular lookahead assertions. The examples on page 248 of the Camel (fourth edition) say that this code 

"0123456789" =~ /(\d{3})/g;

[download]
returns only three strings, '012', '345' and '678', since the regex engine moves past the pattern it's found each time. I tried this in the debugger, and confirmed the behaviour: 
main::(-e:1):   1
  DB<1> $foo = "123456790"

  DB<2> @w1 = ( $foo =~ /(\d{3})/g );

  DB<3> x @w1
0  123
1  456
2  790

[download]

Now, I'm interested in a regex that also finds '123' and '234' -- I want to tell the regex engine to reset to where it found the last match, plus one character. The Camel appears to say that the next example does this, with the lookahead assertion as follows: 

"0123456789" =~ /(?:(\d{3}))/g;

[download]
Brimming with energy and thrilled at my discovery, I try that out in the debugger: 
  DB<4> @w2 = ( $foo =~ /(?:(\d{3}))/g );

  DB<5> x @w2
0  123
1  456
2  790

[download]
Nope. Can someone suggest what I've done wrong?

Update: As noted below, this is a typo, as recorded on the errata page for this book. I'll be going through the rest of the errata and making updates to my Programming Perl (4th edition) later today.

Alex / talexb / Toronto

Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.

In reply to Lookahead assertion by talexb

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.