Normal if-else statement:

if (empty($v)) {
$action = 'default';
} else {
$action = $v;
}

Replacing the above 5 lines of code with just one line of code:

$action = (empty($v)) ? 'default' : $v;

This might not increase the actual performance of the execution, but it does use fewer lines to code the same thing as well as making it easier to read.  Make sure not to use more than one ternary operator in a single statement, as PHP doesn’t always know what to do in those situations.