目录

PHP 正则表达式函数

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PHP正则表达式简介

正则表达式允许您搜索和替换字符串中的模式。

安装

PHP 正则表达式函数是 PHP 核心的一部分。无需安装即可使用这些功能。

运行时配置

php.ini 中的这些设置可用于限制计算正则表达式时使用的时间或资源量。

Name	Default	Description	Changeable
pcre.backtrack_limit	"1000000"	The maximum number of backtracks that the regular expression engine is allowed to do while evaluating an expression. (available since PHP 5.2)	PHP_INI_ALL
pcre.recursion_limit	"100000"	The maximum recursion depth that the regular expression engine is permitted to reach while evaluating an expression. (available since PHP 5.2)	PHP_INI_ALL
pcre.jit	"1"	When set to "1" this enables PCRE's (Perl-Compatible Regular Expressions) just-in-time compilation. (available since PHP 7.0)	PHP_INI_ALL

PHP 正则表达式函数

Function	Description
preg_filter()	Returns a string or an array with pattern matches replaced, but only if matches were found
preg_grep()	Returns an array consisting only of elements from the input array which matched the pattern
preg_last_error()	Returns an error code indicating the reason that the most recent regular expression call failed
preg_match()	Finds the first match of a pattern in a string
preg_match_all()	Finds all matches of a pattern in a string
preg_replace()	Returns a string where matches of a pattern (or an array of patterns) are replaced with a substring (or an array of substrings) in a given string
preg_replace_callback()	Given an expression and a callback, returns a string where all matches of the expression are replaced with the substring returned by the callback
preg_replace_callback_array()	Given an array associating expressions with callbacks, returns a string where all matches of each expression are replaced with the substring returned by the callback
preg_split()	Breaks a string into an array using matches of a regular expression as separators
preg_quote()	Escapes characters that have a special meaning in regular expressions by putting a backslash in front of them

正则表达式修饰符

修饰符可以更改搜索的执行方式。

Modifier	Description
i	Performs a case-insensitive search
m	Performs a multiline search (patterns that search for the beginning or end of a string will match the beginning or end of each line)
u	Enables correct matching of UTF-8 encoded patterns

正则表达式模式

括号用于查找字符范围：

Expression	Description
[abc]	Find one character from the options between the brackets
[^abc]	Find any character NOT between the brackets
[0-9]	Find one character from the range 0 to 9

元字符

元字符是具有特殊含义的字符：

Metacharacter	Description
\|	Find a match for any one of the patterns separated by \| as in: cat\|dog\|fish
.	Find just one instance of any character
^	Finds a match as the beginning of a string as in: ^Hello
$	Finds a match at the end of the string as in: World$
\d	Find a digit
\s	Find a whitespace character
\b	Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b
\uxxxx	Find the Unicode character specified by the hexadecimal number xxxx

量词

量词定义数量：

Quantifier	Description
n+	Matches any string that contains at least one n
n*	Matches any string that contains zero or more occurrences of n
n?	Matches any string that contains zero or one occurrences of n
n{x}	Matches any string that contains a sequence of X n's
n{x,y}	Matches any string that contains a sequence of X to Y n's
n{x,}	Matches any string that contains a sequence of at least X n's

笔记：如果您的表达式需要搜索特殊字符之一，您可以使用反斜杠 (\) 来转义它们。例如，要搜索一个或多个问号，您可以使用以下表达式：$pattern = '/\?+/';

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