php 匹配反斜杠 正则表达式匹配反斜杠的方法

正则表达式匹配反斜杠需要使用四个反斜杠

方法如下：

$subject='\\';

var_dump(preg_match('/^\\\\$/', $subject));

?>

/^\\\$/ /^\\\\$/ 这两个正则表达式 三个或者是四个反斜杠都是匹配的，但是PHP官方文档明确指出需要使用四个反斜杠。

Although 3 slashes may appear to work (don’t ask me why!), the correct way in PHP is definitely to use 4 slashes:

/manual/en/regexp.reference.escape.php

Note:

Single and double quoted PHP strings have special meaning of backslash. Thus if \ has to be matched with a regular expression \\, then "\\\\" or '\\\\' must be used in PHP code.

参考资料