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

I'm new to PHP. I came across this syntax in WordPress. What does the last line of开发者_如何学C that code do?

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

That's the ternary operator:

That line translates to

if ($page)
    $page = $page;
else
    $page = 'default';

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.

It's a ternary operation which is not PHP or WordPress specific, it exists in most langauges.

(condition) ? true_case : false_case 

So in this case the value of $page will be "default", when $page is something similar to false — otherwise it will remain unchanged.

It means that if $page does not have a value (or it is zero), set it to 'default'.

It means if the $page variable is not empty then assign the $page variable on the last line that variable or set it to 'default' page name.

It is called conditional operator

More verbose syntax of the last line is:

if ($page)
{
    $page = $page;
}
else
{
    $page = 'default';
}

That's the so-called conditional operator. It functions like an if-else statement, so

$page = $page ? $page : 'default';

does the same as

if($page)
{
    $page = $page;
}
else
{
    $page = 'default';
}