proc_open() is similar to popen() but provides a much greater degree of control over the program execution. cmd is the command to be executed by the shell. descriptorspec is an indexed array where the key represents the descriptor number and the value represents how PHP will pass that descriptor to the child process. pipes will be set to an indexed array of file pointers that correspond to PHP's end of any pipes that are created. The return value is a resource representing the process; you should free it using proc_close() when you are finished with it.
PHP 5RC2 introduces pty support for systems with Unix98 ptys. This allows your script to interact with applications that expect to be talking to a terminal. A pty works like a pipe, but is bi-directional, so there is no need to specify a read/write mode. The example below shows how to use a pty; note that you don't have to have all descriptors talking to a pty. Also note that only one pty is created, even though pty is specified 3 times. In a future version of PHP, it might be possible to do more than just read and write to the pty.
The file descriptor numbers in descriptorspec 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.
Nota: Windows compatibility: Descriptors beyond 2 (stderr) are made available to the child process as inheritable handles, but since the Windows architecture does not associate file descriptor numbers with low-level handles, the child process does not (yet) have a means of accessing those handles. Stdin, stdout and stderr work as expected.
Nota: If you only need a uni-directional (one-way) process pipe, use popen() instead, as it is much easier to use.