descriptorspec
An indexed array where the key represents the descriptor number and the value represents how PHP will pass that descriptor to the child process. 0 is stdin, 1 is stdout, while 2 is stderr.
The currently supported pipe types are file, pipe and pty.
The file descriptor numbers are not limited to 0, 1 and 2 - you may specify any valid file descriptor number and it will be passed to the child process. This allows your script to interoperate with other scripts that run as "co-processes". In particular, this is useful for passing passphrases to programs like PGP, GPG and openssl in a more secure manner. It is also useful for reading status information provided by those programs on auxiliary file descriptors.
