What does this syntax ( page = $page ? $page : 'default' ) in PHP mean?

Question

I'm new to PHP. I came across this syntax in WordPress. What does the last line of that code do?

$page = $_SERVER['REQUEST_URI'];
$page = str_replace("/","",$page);
$page = str_replace(".php","",$page);
$page = $page ? $page : 'default'

Answer 1

It's an example of the conditional operator in PHP.

It's the shorthand version of:

if (something is true ) {
    Do this
}
else {
    Do that
}

See Using If/Else Ternary Operators http://php.net/manual/en/language.operators.comparison.php.