To use the constant simply use its name:
if (EARTH_IS_FLAT) {
print "Earth is flat";
}
print APP_ENV_UPPERCASE;
or if you don't know the name of the constant in advance, use the constant
function:
// this code is equivalent to the above code
$const1 = "EARTH_IS_FLAT";
$const2 = "APP_ENV_UPPERCASE";
if (constant($const1)) {
print "Earth is flat";
}
print constant($const2);