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

PCRE 模式
escapeshellcmd() - shell 元字符转义

用户评论:

[#1] ian at broster dot co dot uk [2014-09-08 14:22:10]

Note that slash '/' is not one of the special characters, the italic writing of the list above makes pipe '|' look like '/'.

[#2] zooly [2009-07-21 01:07:11]

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

[#3] frostschutz [2009-03-20 02:01:13]

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 [].

[#4] krishoog at gmail dot com [2008-10-13 07:51:57]

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.

[#5] bizzigul at hotmail dot fr [2008-07-30 09:10:07]

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...

[#6] Anonymous [2007-12-26 15:13:11]

Wondering why your preg_replace fails, even if you have used preg_quote?

Try adding the delimiter / - preg_quote($string, '/');