Operation example of PHP preg match regular expression function

The preg_match() function in php is a commonly used function used to execute regular expressions. Regular expressions are used in almost all programming languages. This example introduces the application of the regular expression preg_match function in PHP.

preg_match() function is used for regular expression matching, returning 1 successfully, otherwise returning 0.

preg_match() will stop matching after one successful match. If you want to match all results, you need to use the preg_match_all() function.

Syntax:

preg_match (pattern , subject, matches)

Example:

This example matches strings with uppercase letters followed by . and spaces, Only J. can be matched, because preg_match() will stop matching after one successful match, and will not match again.

<?php
$str="Daniel J. Gross Catholic High School A. is a faith and family based community committed to developing Christian leaders through educational excellence in the Marianist tradition.";
if(preg_match("/[A-Z]. /",$str,$matches)){
print_r($matches);
}
?>

##Output result:

Array ( [0] => J. )

Let’s introduce preg_match to you String length problem

preg_match regular extracts the target content, there is a problem with life and death, and the code is tested to death.

Later I suspected that PHP's preg_match had a string length limit. Sure enough, I found that the value of "pcre.backtrack_limit" was only set to 100000 by default.

Solution:

ini_set('pcre.backtrack_limit', 999999999);

Note: This parameter is available after PHP 5.2.0 version.

In addition, let’s talk about: pcre.recursion_limit

pcre.recursion_limit is the recursion limit of PCRE. If this item is set to a large value, it will consume the available stacks of all processes and eventually cause PHP to crash. .

You can also limit it by modifying the configuration:

ini_set('pcre.recursion_limit', 99999);

In actual project applications, it is best to limit the memory. : ini_set('memory_limit', '64M'); , this is more secure.

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