Constants

• 
  // Set today's date as a constant:
  define ('TODAY', 'August 28, 2007');
  
  // Print a message, using predefined constants and the TODAY constant:
  echo '
  Today is ' . TODAY . '.
  This server is running version ' . PHP_VERSION . ' of PHP on the ' . PHP_OS . ' operating system.
  ';
  
  

The output is shown below

Today is August 28, 2007.
This server is running version 5.2.17 of PHP on the Linux operating system.