PHP preg_replace（）与空格和新行不匹配：为什么？

Question

I'm trying to code a script that removes comments from HTML, except those that begin with [ or !. For example, the comments below should be removed:

<!-- one line comment -->

<!-- multiple line comment -->

The following should not be removed:

<!-- ! one line comment -->

<!--! one line comment -->

<!--! multiple line comment -->

<!-- ! multiple line comment -->

<!-- !multiple line comment -->

<!--[if lt IE 9]>

I'm trying to run the following:

$html = preg_replace('/<!--[\s ]*[^![].*-->/Uis', '', $html);

But it doesn't match the first class of characters (any quantity of spaces and new lines). For example, <!-- !test --> is removed from HTML, while <!--!test --> is not.

What's wrong?

Answer 1

Add + after <!--[\s ]* in your pattern :

$pattern = '<!--[\s
]*+[^![].*-->';

$string = '<!-- one line comment -->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!--
multiple line comment
-->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!-- ! one line comment -->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!--! one line comment -->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!--!
multiple line comment
-->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!-- !
multiple line comment
-->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!--
!multiple line comment
-->';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

$string = '<!--[if lt IE 9]>';
var_dump(preg_replace('/' . $pattern . '/Uis', '', $string));

Output :

string '' (length=0)

string '' (length=0)

string '<!-- ! one line comment -->' (length=27)

string '<!--! one line comment -->' (length=26)

string '<!--!

multiple line comment

-->' (length=33)

string '<!-- !

multiple line comment

-->' (length=34)

string '<!--

!multiple line comment

-->' (length=33)

string '<!--[if lt IE 9]>' (length=17)