There are also so-called. constant, or character identifiers whose values can not be changed. Permanent is used without a dollar sign at the beginning.
Permanent set by PHP
The name of the script file that is currently being processed.
The line number in the script that is currently being processed.
A string representing the version of the PHP parser.
The name of the operating system that runs the PHP parser.
The logical truth value.
Boolean value false.
Constants may be defined by the user using the define (), which takes two parameters: the name of the constant, and the value assigned to it.
define ( “CONSTANT”, “Hello world.”);
echo CONSTANT; // Displays “Hello world.”