remove special characters and punctuations from string

I have a function that gets all the hashtag words in a post and outputs the words separated by a comma (because a post can have many hashtags) to be stored in a database column.

function getHashtags ($text) {
    // explode on spaces
    $text = explode(" ", $text);
    $hashtag = "";
    $hashReg = "/^[a-zA-Z0-9]+$/";
    // for every word in post
    foreach ($text as $word) {
        // 1st character #
        $char = substr($word, 0, 1);
        // word after character #
        $ref = substr($word, 1);
        // if 1st character in word is #
        if ($char == "#") {
            // check if only letters & numbers
            if (preg_match ($hashReg, $ref)) {
                // check hashtag length
                if (strlen($ref) <= 11) {
                    // set hashtag
                    $hashtag .= substr($word, 1).",";
                }
            }
        }
    }
    return $hashtag;
}

The function works well, e.g

$post = "#rock #music is good";
echo getHashtags($post);

// output: rock,music,

However if the example was $post="#rock, #music, is good" the comma after #rock and #music will make the function not work, this will also happen with any other characters like fullstops, question marks etc. I have tried adding a preg_replace('/[^A-Za-z0-9]/', '', $post) but it does not work. How can I fix it so that #rock, #music, or #rock. #music. will still output the desired result of rock,music

You can simple use preg_replace to remove all characters and spaces between the tags and then explode it with #.

Example:

function getHashtags ($text) {
    $clean = preg_replace("/[^A-Za-z0-9] #/", "#", $text);
    
    $text = explode("#", $clean);

    $hashtag = [];

    foreach ($text as $word) {
        if ($word){
            $hashtag[]= $word;
        }
    }
    
    return implode(',', $hashtag);
}

Output should be:

getHashtags("#rock, #music, is good, #metal, #is not so good");
=> string(40) "rock,music, is good,metal,is not so good"

To handle the case where hashtags are separated by non-alphanumeric characters, you can modify the regular expression used to match hashtags. Currently, the regular expression /^[a-zA-Z0-9]+$/ matches only alphanumeric characters.

You can update it to allow for non-alphanumeric characters that might appear between the '#' symbol and the actual hashtag word. One way to do this is to use a character class that matches any non-space character, like this:

$hashReg = "/^#[^\s]+$/";

Here is the modified getHashtags function:

function getHashtags($text) {
    // explode on spaces
    $text = explode(" ", $text);
    $hashtags = [];
    $hashReg = "/^#[^\s]+$/";
    // for every word in post
    foreach ($text as $word) {
        // 1st character #
        $char = substr($word, 0, 1);
        // word after character #
        $ref = substr($word, 1);
        // if 1st character in word is #
        if ($char == "#") {
            // check if hashtag matches pattern
            if (preg_match($hashReg, $word)) {
                // check hashtag length
                if (strlen($ref) <= 11) {
                    // add hashtag to array
                    $hashtags[] = $ref;
                }
            }
        }
    }
    // join hashtags with comma and return as string
    return implode(",", $hashtags);
}