two ways you can do it.
In your vars.php file you can make your variable the entire url:
$link1 = "<a href=\"link101.htm\">go to</a>
be sure to escape the parenthesis.
Or you can leave it the way you have it, and in your main file use this:
<?
echo "<a href=\"$link1\">go to</a>";
?>
again, escaping the parenthesis.
I find the first way easier so that if you need to change the link, or the link name, you only have to do it in one file...