[CentOS] associate .php file with php

My php scripts will only run from bash if I run php
followed by the script name.  Some how I remember
having had this setup where it would recognize it was
a php file by just running the script itself ex -
scriptname.php.

Can someone refresh my memory to tell me what I need
to change so it runs just by typing the script name?

thx

centos 3.5

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