Home Course PHP Constants

PHP Constants

by MH RISHAD - 21 Oct 2018

Constants are like variables except that once they are defined they cannot be changed or undefined.

PHP Constants

A constant is an identifier (name) for a simple value. The value cannot be changed during the script.

A valid constant name starts with a letter or underscore (no $ sign before the constant name).

Note: Unlike variables, constants are automatically global across the entire script.

Create a PHP Constant

To create a constant, use the define() function.




  • 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:


define("GREETING", "Welcome to!");

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


define("GREETING", "Welcome to!", true);
echo greeting;


Constants are Global

Constants are automatically global and can be used across the entire script.

The example below uses a constant inside a function, even if it is defined outside the function:


define("GREETING", "Welcome to!");

function myTest() {
    echo GREETING;




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