It should be noted that the forward slash is not escaped. Since many regexes are surrounded by forward slashes, if you have one in your regex as text you must escape it yourself otherwise it'll terminat the regex.
(PHP 4, PHP 5, PHP 7)
preg_quote — 转义正则表达式字符
$str
[, string $delimiter = NULL
] ) : string
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： . \ + * ? [ ^ ] $ ( ) { } = ! < > | : -
注意 / 不是正则表达式特殊字符。
Note:
注意：preg_quote() 的应用场景不是用于 preg_replace() 的 $replacement 字符串参数。
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。 / 是最常见的分隔符。
返回转义后的字符串。
| 版本 | 说明 |
|---|---|
| 5.3.0 | 字符 - 被增加为需要转义的。 |
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);
?>
Note: 此函数可安全用于二进制对象。
It should be noted that the forward slash is not escaped. Since many regexes are surrounded by forward slashes, if you have one in your regex as text you must escape it yourself otherwise it'll terminat the regex.
If you find yourself using too much of preg_quote(), it's a good sign you might want to use Prepared Patterns from T-Regx library: https://t-regx.com/docs/handling-user-input
List of specials is incomplete:
--- sample code ---
$specials = '.\+*?[^]$(){}=!<>|:-';
for ($i = 0; $i <= 255; $i++) {
if (chr($i) !== preg_quote(chr($i))) {
printf("Character 0x%02x quoted%s\n",
$i,
(strpos($specials, chr($i)) === FALSE) ? ' (+)' : '');
} /* if */
} /* for */
--- sample code ---
--- output ---
Character 0x00 quoted (+)
Character 0x21 quoted
Character 0x24 quoted
Character 0x28 quoted
Character 0x29 quoted
Character 0x2a quoted
Character 0x2b quoted
Character 0x2d quoted
Character 0x2e quoted
Character 0x3a quoted
Character 0x3c quoted
Character 0x3d quoted
Character 0x3e quoted
Character 0x3f quoted
Character 0x5b quoted
Character 0x5c quoted
Character 0x5d quoted
Character 0x5e quoted
Character 0x7b quoted
Character 0x7c quoted
Character 0x7d quoted
--- output ---
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
Wondering why your preg_replace fails, even if you have used preg_quote?
Try adding the delimiter / - preg_quote($string, '/');