PHP Predefined Constants

Useful PHP Predefined Constants defined by the PHP core.

PHP_VERSION - Contains a string with the current PHP version.

echo PHP_VERSION; // 5.5.3

PHP_MAXPATHLEN - The maximum length of filenames (including path) supported by this build of PHP.

echo PHP_MAXPATHLEN; // 260

PHP_OS - Contains a string that can be used to detect the operatig system PHP is running on. Some posible values:
CYGWIN_NT-5.1, Darwin (for Mac Os X), FreeBSD, HP-UX, IRIX64, Linux, NetBSD, OpenBSD, SunOS, Unix, WIN32, WINNT (for Windows NT), Windows, CYGWIN_NT-5.1, IRIX64, SunOS, HP-UX, OpenBSD.

echo PHP_OS; // WINNT

PHP_EOL - The correct 'End Of Line' symbol for the platform on which PHP is running on. Useful to add new lines in strings.

echo 'http://coursesweb.net/'. PHP_EOL .'Next line';

__LINE__ - The current line number of the file.

<?php
// test
echo __LINE__;       // 3

__FILE__ - The full path and filename of the current php file. If used inside an include, the name of the included file is returned.

echo __FILE__; // D:\server\www\file.php

__DIR__ - The directory of the current php file. If used inside an include, the directory of the included file is returned. This is equivalent to: dirname(__FILE__). Not have a trailing slash unless it is the root directory.

echo __DIR__; // D:\server\www

__FUNCTION__ - The function name in which this constant is accessed.

function someName() {
  echo __FUNCTION__;
}
someName();      // someName

__CLASS__ - Returns the class name as it was declared (case-sensitive).

class someClass {
  public function className() {
    return __CLASS__;
  }
}

$obj = new someClass();
echo $obj->className();      // someClass

__METHOD__ - Returns the class method name as it was declared, including the class name (case-sensitive).

class someClass {
  public function someMethod() {
    return __METHOD__;
  }
}

$obj = new someClass();
echo $obj->someMethod();      // someClass::someMethod