PHP Small experience: parsing preg

Regular expressions are applied in PHP
in PHP applications, regular expressions are used primarily for:
• Regular matches: matching the corresponding content according to the regular expression
· Regular substitution: matching content based on regular expressions and replacing
• Regular segmentation: dividing strings based on regular expressions
There are two types of regular expression functions in PHP, one for Perl-compatible regular expression functions and one for POSIX extended regular expression functions. There is little difference, and Perl-compatible regular expression functions are recommended, so the following are examples of Perl-compatible regular expression functions.
delimiter
a regular expression function in Perl compatibility mode whose regular expression needs to be written in a delimiter. Any character that is not a letter, number, or backslash () can be used as a delimiter, and usually we use/as a delimiter. See the example below for specific use.
Tip
Although regular expressions are powerful, you should try not to use regular expression functions if you can do it with normal string handlers, because regular expressions are much less efficient. About normal string processing functions. The
preg_match ()
Preg_match () function is used to match a regular expression, returning 1 successfully, or 0.
Syntax:
int Preg_match (string pattern, string subject [, array matches])
parameter description:

Parameters	Description
Pattern	Regular expressions
Subject	Objects that need to match the retrieved
Matches	Optionally, stores an array of matching results, $matches [0] will contain text that matches the entire pattern, $matches [1] will contain text that matches the child pattern in the first captured bracket, and so on

Example 1:

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<?php


if (Preg_match ("/php/i", "PHP is the Web scripting language of choice.", $matches)) {


print "A match was found:". $matches [0];


} else {


print "A match is not found.";


}


?>

Browser Output:

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A match was found:php

In this example, because the I modifier is used, it is case-insensitive to match PHP in the text.
Tips
Preg_match () stops the match after the first match succeeds, and the Preg_match_all () function is used if you want to achieve a match for all the results, that is, to the end of the subject.
Example 2, get the host domain name from a URL:

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<?php


//Get host name from URL


Preg_match ("/^" (http://)? [^/]+)/I "," http://www.jb51.net/index.html ", $matches);


$host = $matches [2];


//From the host name to obtain the following two segment


Preg_match ("/[^./]+.[ ^./]+$/", $host, $matches);


echo "domain name: {$matches [0]}";


?>

Browser Output:

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domain name is: jb51.net

The

Preg_match_all ()
Preg_match_all () function is used to make a regular expression global match, successfully returning the number of times the entire pattern match (possibly 0), or FALSE if the error returns.
Syntax:
int Preg_match_all (string pattern, string subject, array matches [, int flags])
parameter description:

parameter	description
pattern	regular expression
subject	needs to match the retrieved object
matches	store an array of matching results
flags	optional, specify the order in which the matching results are placed in the matches, and the available tags are: preg_pattern_order: By default, the result is sorted so that $matches [0] matches the full pattern, $matches [1] An array of strings that match the child pattern in the first bracket, and so on preg_set_order: Sort results so that $matches [0] is an array of the first set of matches, $matches [1] is an array of the second set of matches, and so on preg_offset_capture: If this tag is set, the matching result for each occurrence is also returned to its subordinateString offset

The following example shows the keyword (PHP) in all <pre></pre> tags in the text to be displayed in red.

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&lt;?php


$str = "&lt;pre&gt; learning PHP is a happy thing." &lt;/pre&gt;&lt;pre&gt; all the phper need to work together! &lt;/pre&gt; ";


$kw = "PHP";


Preg_match_all ('/&lt;pre&gt; (ss]*?) &lt;/pre&gt;/', $str, $mat);


for ($i =0; $i &lt;count ($mat [0]); $i + +) {


$mat [0][$i] = $mat [1][$i];


$mat [0][$i] = str_replace ($kw, ' &lt;span style= ' color: #ff0000 ' &gt; '. $kw. ' &lt;/span&gt; ', $mat [0][$i]);


$str = Str_replace ($mat [1][$i], $mat [0][$i], $str);


}


Echo $str;


?&gt;

Regular matching Chinese characters
regular matching Chinese characters vary slightly according to page encoding:
gbk/gb2312 Encoding: [x80-xff>]+ or [xa1-xff]+
utf-8 encoding: [x{4e00}-x{9fa5}]+/u
Example:

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&lt;?php


$str = "Learning php is a happy thing." ";


Preg_match_all ("/[x80-xff]+/", $str, $match);


//utf-8 use:


//preg_match_all ("/[x{4e00}-x{9fa5}]+/u", $str, $match);


Print_r ($match);


?&gt;

output:

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Array
(
[0] => Array
(
[0] => study
[1] => is a happy thing.
)

)