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

On my server I've php 5.3.14.

I've found a predefined constant: PHP_BIN_DIR

Then, supposing the file name of the executable file is always 'php', $php_cmd = PHP_BIN_DIR.'/php' point to my PHP executable file.