[PHP] replacing everything between 2 strings

[Matt Palermo]

Is there a way to replace everything between 2 given strings if it
exists?  Say I have:
 
$str = "replace anything and everything in here.";
 
Now I want to replace everything between the word "replace" and "here.",
so the new string could read something like this:
 
$str = "replace NOTHING here.";
 
So it keeps the two end points but just replaces everything in the
middle with a new specified string.  Please help me if you can.  Thanks.
 
Matt