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Detailed explanation of metacharacters in regular expressions in PHP (code examples)
- 易达Original
- 2020-05-30 16:54:00166browse
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 '该字符串符合这个规则：/A\/B\/C/<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则：/A\/B\/C/';
}
?>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 '该字符串符合这个规则：<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则：<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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 '该字符串符合这个规则<br/>';
echo "匹配结果为：";
print_r($math);
}else{
echo '该字符串不符合这个规则';
}
?>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
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