PHP Regex - Append String To Words That Begin with "#' Character

How would I go about using regex to add a static string to all words in another string that begin with the hash character? For example, I have the following two variables:

$stringtoappend = "someuniqueID";
$mystring = ".someClass #someID #someOtherID";

After processing the开发者_JAVA技巧 string, I'd like to create the following string:

".someClass #someIDsomeuniqueID #someOtherIDsomeuniqueID";

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Assuming your strings are common CSS names (alphanumeric + dash), use preg_replace() with the following regular expression:

preg_replace('/(#[\w-]+)/', '$1' . $stringtoappend, $mystring);