Re: Regular expressions

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On 10/16/06, Richard Lynch <ceo@xxxxxxxxx> wrote:
On Mon, October 16, 2006 2:54 pm, Chrome wrote:
> *edit* sorry I didn't think and just hit reply on this instead of
> reply
> all... sorry Richard */edit*
>
> [snip]
> .*? is kinda silly -- .* mean "0 or more characters", and ? means
> "maybe"
> but putting them together has no added value, so lose the ?
> [/snip]
>
> I could be wrong (and under the considerable knowledge of Richard I
> certainly feel it :) ) but doesn't the ? after a quantifier signify
> that
> preceding pattern is to be taken as ungreedy?

You're right; I'm wrong.

I'm not PCRE expert.

Took me 20 years to be able to stumble through the simplest expressions.

? means "maybe" in some other place in PCRE.  Or maybe that's POSIX.
Never have figured that one out.

The ? after * means ungreedy only.. so your basic:
 a? means a or no a in the regular usage

The easiest to remember is that ? two basic definitions:
 - extend the meaning of
 - 0 or 1 of the previous expression



/foo(?i)bar/

matches FOoBar, fOObar, foobar.. the (?i) extends the meaning of
(?[modifer-list])  to contain modifiers of the previous expression and
no more

/foo.*?bar/
 is the same thing as saying /foo.*(?U)bar; a short cut, much like
what \d is a shortcut to [0-9]

/foo(?<....)/
 a look behind assertion

/foo(?=...)/
 a look ahead assertion

(and a negative of the  assertions are allowed)

/foo(?(condition)yes:no)/
 condition usually being an assoertion of some sort


I still dont understand it, and it is one of the reasons why people
have problems using regex, it really is a whole different language,
using Regex Coach as chrome did, is the probably the best way to find
out the problem or how to match what you are looking for...

A nice little overview (although i have read it about a few dozen
times and still cant apply the logic 100% of the time)
php.net/reference.pcre.pattern.syntax.php

on the other hand, people still want html parsers written in PCRE.. :)


Curt.

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