Understanding Pattern Parameters

[Wstar]

Can someone please explain the "/(<([\w]+)[^{>]>)(.?)(<\/\2>)/"} part of the preg_match_all functions? Or a site that can explain them all?

Note: This code is on php.net and finds matching tags.
http://us.php.net/preg_match_all

<?php
// The \\2 is an example of backreferencing. This tells pcre that
// it must match the second set of parentheses in the regular expression
// itself, which would be the ([\w]+) in this case. The extra backslash is
// required because the string is in double quotes.
$html = "<b>bold text</b><a href=howdy.html>click me</a>";

preg_match_all("/(<([\w]+)[^>]*>)(.*?)(<\/\\2>)/", $html, $matches, PREG_SET_ORDER);

foreach ($matches as $val) {
    echo "matched: " . $val[0] . "\n";
    echo "part 1: " . $val[1] . "\n";
    echo "part 2: " . $val[2] . "\n";
    echo "part 3: " . $val[3] . "\n";
    echo "part 4: " . $val[4] . "\n\n";
}
?>

[NogDog]

PCRE pattern syntax
PCRE pattern modifiers (after the closing delimiter)

By using a different delimiter ("#" instead of "/") and getting rid of the first set of square brackets since they are redundant, we can clean that pattern up a bit to:

preg_match_all("#(<(\w+)[^>]*>)(.*?)(</\\2>)#", $html, $matches, PREG_SET_ORDER);

#      : opening regexp delimiter
(      : start sub-pattern
<      : literal "<"
(      : start sub-pattern #2
\w     : any "word" character (letter, number, or underscore)
+      : preceding character appears 1 or more times
)      : end sub-pattern #2
[^>]   : any character that is not a ">"
*      : preceding character class appears 0 or more times
     : literal ">"
)      : end of sub-pattern
(      : start of sub-pattern
.      : any character
*      : preceding character appears 0 or more times
?      : preceding repetition modifier's greediness is toggled (to "ungreedy" in this case)
)      : end sub-pattern
(      : start sub-pattern
</     : literal "</"
\\2    : whatever was matched in sub-pattern #2
     : literal ">"
)      : end of sub-pattern
#      : closing regexp delimiter

Clear as mud? 😉

[mpb001]

http://xkcd.com/208/

Explains all you ever need to know about regualr rexpressions. Understand them and be Tarzan.
( NogDog gave you all you need to open the box, you just have to deal with Pin Head while you open it and close it. )

http://xkcd.com/292/

For all you need to know about gotos. Velociraptors understand the consequence far more than most developers( not really relevant but I like the this cartoon also).

[nrg_alpha]

mpb001;10926999 wrote:

http://xkcd.com/208/

Explains all you ever need to know about regualr rexpressions. Understand them and be Tarzan.

..........Huh!?

[NogDog]

nrg_alpha;10927002 wrote:

..........Huh!?

Did you view the comic?

[nrg_alpha]

NogDog;10927003 wrote:

Did you view the comic?

I did.. the guy's using perl.. so is the suggestion of that post to use perl instead? We're talking about a php environment, here, not perl.

[NogDog]

nrg_alpha;10927006 wrote:

I did.. the guy's using perl.. so is the suggestion of that post to use perl instead? We're talking about a php environment, here, not perl.

Methinks you may be reading too much into that post.

• PCRE = Perl-Compatible Regular Expression.
• Comic is about using a regexp to solve the problem.
• They happen to be using Perl in that instance.
• Therefore, I thought it was (somewhat) funny, which I think was the only intent of posting it.

:p

[nrg_alpha]

I suppose the humor is lost for me here. I figured the insinuation was to to use perl's own regex system as opposed to using pcre.