Detailed explanation of metacharacters in regular expressions in PHP (code examples)

Objectives of this article:

1. Understand the definition of metacharacters in regular expressions

2. Master the usage of metacharacters in basic regular expressions

(1) , Understand the definition of regular expression metacharacters

Characters with special meanings in regular expressions are called metacharacters. Common metacharacters are:

\, ^, $, [ ,],|,(,),?*, ,{,}

(2) Master the usage of metacharacters in basic regular expressions

Summary:

1, \ are generally used to escape characters
2, ^ represents the starting position of the target (or the beginning of the line in multi-line mode)
3, $ represents the end position of the target (or in multi-line mode) In line mode, it is the end of the line)
4. By default, it matches any character except the newline character
5. [ means the definition start character
6, ] means the definition end character
7, | Indicates an optional branch
8, (Indicates the start tag of a subgroup
9,) Indicates the end tag of a subgroup
10, ?: As a quantifier, it indicates 0 or 1 matches.
11, *: As a quantifier, it means 0 or more matches
12, : As a quantifier, it means 1 or more matches
13, {: It means the start mark of a custom quantifier
14. }: Indicates the end tag of a custom quantifier

The following codes are used one by one to practice each summary, which can promote understanding

1. \ is generally used for escaping The specific code of the character

is as follows:

<?php
$p = "/A\/B\/C/";//包含A/B/C字符串
$str = "A/B/C";
if (preg_match($p, $str,$math)) {
    echo &#39;该字符串符合这个规则：/A\/B\/C/<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则：/A\/B\/C/&#39;;
}
?>

The running result is:

This string conforms to this rule: /A\/B\/C/
The matching result is: Array ([0] => A/B/C)

2, ^ represents the starting position of the target (or the beginning of the line in multi-line mode)

The specific code is as follows:

<?php
$p = "/^A/m";//以A开始
$str = "Abc \nAcc \nAdd";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则：<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is as follows:

The string conforms to this rule:
The matching result is: Array ( [0] => ; Array ( [0] => A [1] => A [2] => A ) )

3, $ represents the end position of the target (or in multi-line mode is the end of the line)

The specific code is as follows:

<?php
$p = "/A$/m";//以A结尾的字符串
$str = "nihao A\n this is a word A";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则：<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule:
The matching result is: Array ( [0] => Array ( [0] => A [1] => A ) )

4, . By default, matches any character except newline characters

The specific code is as follows:

<?php
$p = "/A.B/";//查找A（任何字符除了换行符外）B的字符串
$str = "A,B A-B A\nB";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule
The matching result is: Array ( [0] => ; Array ( [0] => A,B [1] => A-B ) )

5, [ represents the definition start character

6, ] represents the definition end character

The specific code is as follows:

<?php
$p = "/[0-9]A/";//包含小于9的一个数字和A
$str = "0A 1A 2A SA";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule
The matching result is: Array ( [0] => ; Array ( [0] => 0A [1] => 1A [2] => 2A ) )

7, | represents an optional branch

specific The code is as follows:

<?php
$p = "/[0-9]A|[0-9]B/";//查找小于9的一个数字和A相连的字符串或者查找
                        //小于9的一个数字和B相连的字符串
$str = "0A 1A 2B 3C";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule
The matching result is: Array ( [0] => Array ( [0] = > 0A [1] => 1A [2] => 2B ) )

8, (Indicates the start tag of a subgroup

9,) Indicates a subgroup The end tag of the group

<?php
$p = "/([0-9])-([0-9])/";
$str = "1-3 2-4 3-s";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule
The matching result is: Array ( [0] => Array ( [0] => 1-3 [1] => 2-4 ) [1] => Array ( [0] => 1 [1] => 2 ) [2] => Array ( [0] => 3 [1] => 4 ) )

10, ?: As a quantifier, it means 0 or 1 matches.

The specific code is as follows:

<?php
$p = "/(A[0-9])?H/";//查找H字符 因为?表示出现0或者1次
$str = "A1AH AsH BH";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is as follows:

The string conforms to this rule
The matching result is: Array ( [0] => ; Array ( [0] => H [1] => H [2] => H ) [1] => Array ( [0] => [1] => [2] => ; ) )

11, *: as a quantifier, indicating 0 or more matches

<?php
$p = "/(A[0-9])*H/";//查找H字符 因为*表示出现0或者多次所以和?的结果不同
$str = "A1AH A1H A2H A2A2H";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

This string matches The matching result of this rule
is: Array ( [0] => Array ( [0] => H [1] => A1H [2] => A2H [3] => A2A2H ) [1 ] => Array ( [0] => [1] => A1 [2] => A2 [3] => A2 ) )

12. : As a quantifier, Indicates 1 or more matches

The specific code is as follows:

<?php
$p = "/(A[0-9])+H/";//查找H字符 前面至少包含A和一个<9的数字相连
$str = "A1AH A1H A2H A2A2H";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is as follows:

The string conforms to this rule
The matching result is: Array ( [0] => Array ( [0] => A1H [1] => A2H [2] => A2A2H ) [1] => Array ( [0] => A1 [1] => A2 [2] => A2 ) )

13, { : Represents the start tag of the custom quantifier

14, } : Represents the end tag of the custom quantifier

The specific code is as follows:

<?php
$p = "/d{2}/";//查找2个d的字符串
$str = "dd和dd和ddd";
if (preg_match_all($p, $str,$math)) {
    echo &#39;该字符串符合这个规则<br/>&#39;;
    echo "匹配结果为：";
    print_r($math);
}else{
    echo &#39;该字符串不符合这个规则&#39;;
}
?>

The running result is:

The string conforms to this rule
The matching result is: Array ( [0 ] => Array ( [0] => dd [1] => dd [2] => dd ) )

Summary:

1. Understand regular rules Definition of expression metacharacters

2. Master the basic usage of metacharacters in regular expressions

The above is the detailed content of Detailed explanation of metacharacters in regular expressions in PHP (code examples). For more information, please follow other related articles on the PHP Chinese website!