calling a file inside another file in php

[retro826]

a.php which contains \[code\]<?php echo "i'm a.php"; ?>\[/code\]and b.php which contains \[code\]<?php echo "i'm b.php";// some code here to "execute" a.php so that it prints i'm a.php as the output.?>\[/code\]so finally, when i click on b.php it should display:i'm b.phpi'm a.php