How to get Variable from Regex in PHP? - php

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, '$0', $str);
return($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
)
)