Get current PHP executable from within script?

Question

I want to run a PHP cli program from within PHP cli. On some machines where this will run, both php4 and php5 are installed. If I run the outer program as

Answer 1

Worth noting that now in PHP 5.4+ you can use the predefined constant - PHP_BINARY:

PHP_BINARY

Specifies the PHP binary path during script execution. Available since PHP 5.4.