Lazy, Greedy, or What? Looking for a definitive Regex reference

Question

Recently, somewhere on the web*, I found a reference for regular expressions which described a "third way" of greediness, different both from greedy (.*) and lazy (.*?) matching.

I've now tried searching SO, Googling, and even searching my browser history, but to no avail.

Can anyone make a good guess at what it was I saw?

Clarification: it referred to what was for me a new construct (something like .*+), and I believe it even had a name for it (something like, but probably not, "passively greedy").

* I appreciate that "somewhere on the web" is about as helpful as "in the Library of Babel" or "in the Mandelbrot set", but please try to help

Well, well, six years later somebody finally downvoted this question. Would you care to share with us what your criticism is? That way we can learn, and improve. Alternatively, if you were just having a bad day, you can always vote it back up again when life gets better. — Brent.Longborough, Jan 27 '15 at 17:18
The dv is probably because your question is vague and has no context. This page is provably low-value to researchers because it has been on SO for over a decade and has very few upvotes -- anywhere on the page. — mickmackusa, Jul 05 '21 at 09:22

score 5 · Answer 1 · edited Jun 20 '20 at 09:12

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I think you are referring to "posessive" matching. Java describes it on this page: http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html

Possessive quantifiers, which greedily match as much as they can and do not back off, even when doing so would allow the overall match to succeed.

The syntax is the same as what you described (.*+) .

edited Jun 20 '20 at 09:12

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answered Feb 19 '09 at 20:10

Adam Crume

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Sorry to have un-accepted your answer, but I believe Bennett McElwee has the better reference. – Brent.Longborough Feb 19 '09 at 20:38

score 4 · Answer 2 · answered Feb 19 '09 at 19:54

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This maybe? http://www.regular-expressions.info/repeat.html

An Alternative to Laziness

In this case, there is a better option than making the plus lazy. We can use a greedy plus and a negated character class: <[^>]+>.

answered Feb 19 '09 at 19:54

mletterle

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That's a good reference, but doesn't appear to have what I thought I saw... Thanks – Brent.Longborough Feb 19 '09 at 20:01
It had, in fact, what I was looking for, a bit further down the tutorial. Sorry I can't upvote a second time... – Brent.Longborough Feb 19 '09 at 20:56
I only see one plus sign; there should be two: <[^>]++> – Alan Moore Feb 22 '09 at 21:46

score 2 · Accepted Answer · answered Feb 19 '09 at 20:32

There are various different regex packages. PCRE (Perl-compatible regular expressions) are used (more or less) in Perl, Java, PHP and probably other languages. The PCRE man page might be regarded as the definitive reference. It describes possessive quantifiers (e.g. *+ and ++), which are a shorthand for atomic groups.

score 1 · Answer 4 · answered Feb 19 '09 at 19:51

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Well, not exactly a reference, but good still. Mastering Regular Expressions

There is also a "reference" book from O'Reilly, but I can't testify on it. Just saw it for the first time.

answered Feb 19 '09 at 19:51

Rook

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score 0 · Answer 5 · answered Feb 19 '09 at 20:12

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I always keep a copy of this regular expressions cheat sheet handy in my cube.

answered Feb 19 '09 at 20:12

Barry

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score 0 · Answer 6 · answered Feb 19 '09 at 20:54

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Thank you all. The key to getting my memory back was "possessive", not "passive".

Here are a couple of useful references:

Perldoc, under subheading "Quantifiers"
In the regular-expressions.info tutorial

answered Feb 19 '09 at 20:54

Brent.Longborough

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Lazy, Greedy, or What? Looking for a definitive Regex reference

6 Answers6