为什么我的RegEx只有在包含一些额外字符时才会结束？

Question

Okay, let's say I'm trying to parse this:

href="http://google.com">Website</a>

This doesn't work:

preg_match('/href="http:\/\/(.+)">/', $a, $b);

But this does:

preg_match('/href="http:\/\/(.+)">Website/', $a, $b);

Why is this? The first one just keeps going to the end of the string.

Answer 1

Greedy selector

The problem here is that your selector is greedy - it will match the longest possible string it can:

preg_match('/href="http:\/\/(.+)">/', $a, $b);

Since you use "any character" (.) it is matching right up until the very last occurrence of "> that exists in the input string.

None-greedy selector

If you make the selector none-greedy, then it will stop at the shortest possible match:

preg_match('/href="http:\/\/(.+?)">/', $a, $b);

Note the extra ? in the regex pattern, which modifies the "one or more" (+) operator to be none greedy.

You can also make all selectors none-greedy by default by using the u modifier:

preg_match('/href="http:\/\/(.+)">/u', $a, $b);