如何使用正则表达式提取字符串？

Can I extract the string aaa without using subpatterns (but still using regexp)?

$str = 'abc#aaa#abc';
preg_match('/#(.*)#/', $str, $matches);
print_r($matches);

Update

• lookahead and lookbehind is a second solution, any other ?

I'm just trying to figure out some regexp alternatives !

/(?<=#).*?(?=#)/

But why wouldn't you want to use a capturing group?

Alternative to look-ahead / look-behind assertions:

echo preg_replace('/^.*?#|#.*?$/s', '', 'abc#aaa#abc');