proc_open()'s $cwd argument

proc_open_cwd.php

$ cat proc_open_cwd.php 
<?php
$fdSpecs = array(
    1 => array('pipe', 'w'),
    2 => array('pipe', 'w'),
);
$process = proc_open('php -r "var_dump(getcwd());"', $fdSpecs, $pipes);
echo 'Without $cwd argument:', PHP_EOL;
echo stream_get_contents($pipes[1]);

echo PHP_EOL;

$process = proc_open('php -r "var_dump(getcwd());"', $fdSpecs, $pipes, NULL);
echo 'With NULL as $cwd argument:', PHP_EOL;
echo stream_get_contents($pipes[1]);

echo PHP_EOL;

$process = proc_open('php -r "var_dump(getcwd());"', $fdSpecs, $pipes, getcwd());
echo 'With getcwd() as $cwd argument:', PHP_EOL;
echo stream_get_contents($pipes[1]);

echo PHP_EOL;

$process = proc_open('php -r "var_dump(getcwd());"', $fdSpecs, $pipes, '/');
echo 'With "/" as $cwd argument:', PHP_EOL;
echo stream_get_contents($pipes[1]);

result.txt

$ php proc_open_cwd.php
Without $cwd argument:
string(29) "/Users/yuya/dev/php/proc_open"

With NULL as $cwd argument:
string(29) "/Users/yuya/dev/php/proc_open"

With getcwd() as $cwd argument:
string(29) "/Users/yuya/dev/php/proc_open"

With "/" as $cwd argument:
string(1) "/"