Basics and simple examples of PHP regular expressions

Writing regular expressions is often a headache. You may not understand the regular expression you just wrote after a while. This article introduces the basic syntax of regular expressions and simple PHP code examples, which is convenient for friends to read when they need to write regular expressions.

The ^ at the beginning and the $ at the end tell PHP to check from the beginning to the end of the string. Without $, the program would still match to the end.

[ and ] are used to limit the allowed input types. For example a-z allows all lowercase letters, A-Z allows all uppercase letters, 0-9 all numbers, etc., and many more.

{ and } are used to limit the number of characters expected. For example {2,4} means that each section of the string can be 2-4 characters long, such as .com.cn or .info. Here, "." does not count as a character, because the allowed input type defined before {2,4} only has uppercase and lowercase letters, so this paragraph only matches uppercase and lowercase letters

( and ) are used to merge sections , and defines the characters that must be present in the string. (a|b|c) matches a or b or c.

(.) will match all characters, while [.] will only match "." itself.

To use some symbols themselves, you must add a \ in front. These characters are: ( ) [ ] . * ? + ^ | $

Attachment: PCRE syntax guide

/ Delimiter
^ String header
$ End of string
[a-z] All lowercase letters
[A-Z] All uppercase letters
[0-9] All numbers
? Zero or one immediately preceding character
* Zero or more characters immediately preceding
+ One or more characters immediately preceding
{4} 4 characters immediately preceding
{4,8} 4-8 characters immediately preceding Characters
. Any characters
(red|green|blue) Red or green or blue (red or green or blue)
s Space

Special characters (need to add \ in front)
( ) [ ] . * ? + ^ | $

Rule matching preg_match

Using preg_match(), we can complete the rule matching of strings. The preg_match() function returns 1 if a match is found, 0 otherwise. There is an optional third parameter that allows you to store the matched parts in an array. This feature can become very useful when validating data.
$string = "football";
if (preg_match('/foo/', $string)) {
// Match correctly
}

Rule replacement preg_replace

preg_replace allows you to replace strings that match a regular expression you define.
$val = "/*123456789*/abcd";
$pp = preg_replace("/[(\/\*)+(.)(\*\/)+]+/",'fuck ',$val);
print_r($pp);
The result is
fuck123456789fuckabcd

Rule split preg_split

preg_split can divide the entire string by The matched regular expression is split into segments of 1, 2, or more characters. For example, get tags, whether separated by spaces or commas:
$tags = preg_split('/[,]/', 'my,tags,unevenly,spaced');
print_r($tags);
The result is:
Array ( [0] => my [1] => tags [2] => unevenly [3] => spaced )

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