Question

This is a little tricky so bear with me:

• I have a PHP script a.php that is launched from the command line and data is provided to it via STDIN
• I have another PHP script b.php
• I want to have a.php launch b.php and capture its output.
• Also, a.php has to forward the STDIN to b.php

Is there an easy way to do this?

Answer 1

For just capturing the stdout of another program (php or not), you can use backticks:
http://php.net/manual/en/language.operators.execution.php.
For example:

$boutput = `php b.php`;

To capture stdin, do this:

$ainput = file_get_contents('php://stdin');

Finally, to pipe the contents of a string to an external program, use proc_open, as suggested by jeremy’s answer.
Specifically, here’s what your a.php should contain:

$ainput = file_get_contents('php://stdin');
$descriptorspec = array(
        0 => array("pipe", "r"),
        1 => array("pipe", "w"),
        2 => array("pipe", "w")
);
$process = proc_open('php b.php', $descriptorspec, $pipes);
fwrite($pipes[0], $ainput);
fclose($pipes[0]);
echo stream_get_contents($pipes[1]); # echo output of "b.php < stdin-from-a.php"
fclose($pipes[1]);
proc_close($process);