Generating a dynamic "Read More" link

I purchased a theme and I have been making the changes I want to it. By default, there is a “read “more” link on the post page of the blog for each post. The text showing for the post might be the full post or it might be an excerpt.

I only want to show the “read more” if there is more to the actual post.

I found where to make the change in the code (functions.php) but I am very weak in PHP syntax. if I code “echo the_permalink();”, in the conditional code section I get the link to the full post which is what I need. Now I need to concatenate that into an href string but I do not know how.

<a href="[permalink]">read more</a>

Can someone help me out with this?

Thanks in advance