如何在PHP中从Regex获取变量？

Question

How can I get only the Name/Variable which is "regexed"? Like in this case the $1 or $0 in the anchor's href?

When I try to echo the $1 or $0 I get a Syntax Error because it's a Number. At the Moment the $str is a whole Text.

function convertHashtags($str){
    $regex = "/#+([a-zA-Z0-9_]+)/";
    $str = preg_replace($regex, '<a href="hashtag.php?tag=$1">$0</a>', $str);
    return($str);
    }

Answer 1

Simple use preg_match before preg_replace, eg

preg_match($regex, $str, $matches);

Assuming the pattern actually matched, you should have the results in $matches[0] and $matches[1] which are the equivalent of $0 and $1 in the replace string.

FYI, the $n tokens in the replacement string are not variables though I can see how that can be confusing. They are simply references to matched groups (or the entire match in the case of $0) in the regex.

See http://php.net/manual/function.preg-replace.php#refsect1-function.preg-replace-parameters

---

To find multiple matches in $str, use preg_match_all(). It's almost the same only it populates $matches with a collection of matches. Use the PREG_SET_ORDER flag as the 4th argument to make the array workable. For example...

$str = ' xD #lol and #testing';
$regex = '/#(\w+)/';
preg_match_all($regex, $str, $allMatches, PREG_SET_ORDER);
print_r($allMatches);

produces...

Array
(
    [0] => Array
        (
            [0] => #lol
            [1] => lol
        )

    [1] => Array
        (
            [0] => #testing
            [1] => testing
        )

)