PHP 5.4.33 Released

preg_quote

(PHP 4, PHP 5)

preg_quote转义正则表达式字符

说明

string preg_quote ( string $str [, string $delimiter = NULL ] )

preg_quote()需要参数 str 并向其中 每个正则表达式语法中的字符前增加一个反斜线。 这通常用于你有一些运行时字符串 需要作为正则表达式进行匹配的时候。

正则表达式特殊字符有: . \ + * ? [ ^ ] $ ( ) { } = ! < > | : -

参数

str

输入字符串

delimiter

如果指定了可选参数 delimiter,它也会被转义。这通常用于 转义PCRE函数使用的分隔符。 /是最通用的分隔符。

返回值

返回转义后的字符串。

更新日志

版本 说明
5.3.0 字符 - 被增加为需要转义的。

范例

Example #1 preg_quote()示例

<?php
$keywords 
'$40 for a g3/400';
$keywords preg_quote($keywords'/');
echo 
$keywords// 返回 \$40 for a g3\/400
?>

Example #2 将文本中的单词替换为斜体

<?php
//在这个例子中,preg_quote($word) 用于保持星号原文涵义,使其不使用正则表达式中的特殊语义。

$textbody "This book is *very* difficult to find.";
$word "*very*";
$textbody preg_replace ("/" preg_quote($word) . "/",
                          
"<i>" $word "</i>",
                          
$textbody);
?>

注释

Note: 此函数可安全用于二进制对象。

参见

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User Contributed Notes 6 notes

up
11
Anonymous
6 years ago
Wondering why your preg_replace fails, even if you have used preg_quote?

Try adding the delimiter / - preg_quote($string, '/');
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7
krishoog at gmail dot com
5 years ago
To bizzigul at hotmail dot fr:
It's not a good practice to make somthing work *almost* all of the time. If the input contains a '`' you will still get an error. I recommend using the default delimiter ('/') and also feed this to preg_quote as second argument.
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3
zooly
5 years ago
To escape characters with special meaning, like: .-[]() and so on, use \Q and \E.

For example:

<?php echo ( preg_match('/^'.( $myvar = 'te.t' ).'$/i', 'test') ? 'match' : 'nomatch' ); ?>

Will result in: match

But:

<?php echo ( preg_match('/^\Q'.( $myvar = 'te.t' ).'\E$/i', 'test') ? 'match' : 'nomatch' ); ?>

Will result in: nomatch
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2
frostschutz
5 years ago
I wanted to escape a string of characters so I could match them in [], i.e. [.,-!"§$%\\\[\]\^].

Unfortunately preg_quote does not escape the - character which has a special meaning in [], i.e. [a-z].

So I used this hack: make - the delimiter of the expression, i.e.

preg_quote(userinput, "-")
preg_replace("-[$userinput]-u", "", $str)

Apparently using a special char as a delimiter of a regular expression disables this character, i.e. even if it's escaped it's not understood as special character for the expression anymore.

so the pattern "-[a\\-z]-u" matches the characters a, - and z, and not abc...xyz.

It would be nice if preg_quote also escaped characters that have special meanings even if they have this meaning only under certain conditions, such as inside [].
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1
ian at broster dot co dot uk
14 days ago
Note that slash '/' is not one of the special characters, the italic writing of the list above makes pipe '|' look like '/'.
up
1
bizzigul at hotmail dot fr
6 years ago
To prevent any problems, try to always use a delimiter that will *almost* not be used inside the regex, such as ` (back quote)

for example: instead of
<?php preg_match('/foo\/bar\//',$somevar); ?>

use

<?php preg_match('`foo/bar/`',$somevar); ?>

it's that simple! like this, you won't have to bother with delimiters anymore...
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