Insert substring right before first occurrence of another string

Question

Take for example these strings:

  $strOne = "Place new content here:  , but not past the commma.";
  $strTwo = "test content";

So based on the strings above, how do make a new string that looks like this:

  $finalstr = "Place new content here:  test content, but not past the comma.";

EDIT

Also, lets assume I don't have access to $strOne, meaning I want to modify it via string functions not directly the string via concatenation etc...

Answer 1

Try a combination of strpos and substr_replace ?

$strOne = "Place new content here:  , but not past the commma.";
$strTwo = "test content";

// find the position of comma first
$pos = strpos($strOne, ',');
if ($pos !== false)
{
     // insert the new string at the position of the comma
     $newstr = substr_replace($strOne, $strTwo, $pos, 0);
     var_dump($newstr);
}

Output:

string(63) "Place new content here: test content, but not past the commma."