[php] When do I use the PHP constant "PHP_EOL"?

On some system may be useful to use this constant because if, for example, you are sending an email, you can use PHP_EOL to have a cross-system script working on more systems... but even if it's useful sometime you can find this constant undefined, modern hosting with latest php engine do not have this problem but I think that a good thing is write a bit code that saves this situation:

<?php
  if (!defined('PHP_EOL')) {
    if (strtoupper(substr(PHP_OS,0,3) == 'WIN')) {
      define('PHP_EOL',"\r\n");
    } elseif (strtoupper(substr(PHP_OS,0,3) == 'MAC')) {
      define('PHP_EOL',"\r");
    } elseif (strtoupper(substr(PHP_OS,0,3) == 'DAR')) {
      define('PHP_EOL',"\n");
    } else {
      define('PHP_EOL',"\n");
    }
  }
?>

So you can use PHP_EOL without problems... obvious that PHP_EOL should be used on script that should work on more systems at once otherwise you can use \n or \r or \r\n...

Note: PHP_EOL can be

1) on Unix    LN    == \n
2) on Mac     CR    == \r
3) on Windows CR+LN == \r\n

Hope this answer help.