How to make a link on homepage only in WordPress?

rather than a sitewide link if I put it in footer, header or sidebar.php....

 

You'll need to do something similar to this. Put in your sidebar (or other location).

<?php if (is_home()) {
        // show home page only link
        echo "your link here";
}

Code (markup):

 

Oh, that works. Thanks for your advice.

 

Happy to help.