If Statement Help (If user does not have gravatar)

I have something like this:

<?php if(function_exists('get_avatar')){
  echo get_avatar($comment, '32', $default=identicon);
} ?>

(see it in action)

Regarding the “identicon” see:
https://en.blog.wordpress.com/2008/05/04/default-avatars/

Short answer: You don’t. There is no easy way to tell if a user has a gravatar or not. The way it works is that it sticks the correct image code into the page and lets the gravatar server either serve up the gravatar or the default image.

OK, it’s just I have the users select from a range of avatars, and was wondering if I could display a Gravatar if they have one, if not display the one they selected on the comment form.

I’ll just go for one or the other.

Oh. Yeah, you can do that. The third parameter to the get_avatar function is a “default” setting. If they have no avatar, then that one displays.

Like this:
get_avatar( $comment, 96, 'https://example.com/avatar.gif' );

Sorry for the delay, I understand now.

Just one problem with my PHP skills really, how do i go about inserting a PHP statement within the default location, for example:

$default = ‘https://www.mysite.com/print $comment->extra_avatar;.jpg’ );

Obviously the part in bold retrieves the image name, but how do i execute this correctly? I guess I need to escape the quotes somehow?