Core PHP: Constants (2.1)

Constants

Constants are similar to variables except that they cannot be changed or undefined after they've been defined.
Begin the name of your constant with a letter or an underscore.
To create a constant, use the define() function:

define(name, value, case-insensitive)

Parameters:

name: Specifies the name of the constant;
value: Specifies the value of the constant;
case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false;

The example below creates a constant with a case-sensitive name:

<?php
  define("MSG", "Hi Buzz Learners!");
  echo MSG;

   // Outputs "Hi Buzz Learners!"
?>

The example below creates a constant with a case-insensitive name:

<?php
  define("MSG", " Hi Buzz Learners!", true);
  echo msg;

  // Outputs "Hi Buzz Learners!"
?>

No dollar sign ($) is necessary before the constant name.