$res = preg_replace('/(?<=\A|\W)@([\w]+)/ius', '<a href="/users/$1">@$1</a>', $text);$text = '@user_first123 Example text with @user_login123 and #tag and email asdasd@gmail.com';
$res = preg_replace('/(?:\A|\W)@([\w]+)/ius', '<a href="/users/$1">@$1</a>', $text);
$res = preg_replace('/#([\w]+)/ius', '<a href="/tags/$1">#$1</a>', $res);
var_dump($text, $res);string '@user_first123 Example text with @user_login123 and #tag and email asdasd@gmail.com' (length=83)
string '<a href="/users/user_first123">@user_first123</a> Example text with<a href="/users/user_login123">@user_login123</a> and <a href="/tags/tag">#tag</a> and email asdasd@gmail.com' (length=176)