Escaping characters in regular expressions in PHP

Question

The following returns true:

$bool1 = preg_match("/5/", "Your bill is $5.00 dude");
var_dump($bool1);

I expect this because '5' is in the string.But the following returns false:

$bool1 = preg_match("/\$5\./", "Your bill is $5.00 dude");
var_dump($bool1);

I thought I was escaping the $ correctly so that it would look for $5 in the string and find it, but no. Can someone explain? Thanks.

Answer 1

使用单引号来防止PHP误解任何转义：

$bool1 = preg_match('/\$5\./', "Your bill is $5.00 dude"); 

Answer 2

你应该使用preg_quote（）函数进行正确的转义

Answer 3

$bool1 = preg_match('/\$5\./', "Your bill is $5.00 dude");
var_dump($bool1);