What will be the result of executing following cod

What will be the result of executing following code?

$var = "Hello World!";
echo $var ?: "Goodby World!";

Hello world!
Goodby World!
Syntax error
Nothing will be printed

Explanation

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE.
Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.