PHP StdErr after Exec()

In PHP, the exec() function executes a command and returns the output from the command's stdout. However, if the command writes to stderr, this output is not captured by exec().

To capture both stdout and stderr from a command, you can use the proc_open() function. proc_open() provides a greater level of control over the command execution process, including the ability to pipe the command's stdin, stdout, and stderr streams.

Example:

Let's consider the following shell script, test.sh, which writes to both stderr and stdout:

#!/bin/bash

echo 'this is on stdout';
echo 'this is on stdout too';

echo 'this is on stderr' >&2;
echo 'this is on stderr too' >&2;

To execute this script in PHP and capture both stdout and stderr, you can use the following code:

$descriptorspec = [
    0 => ['pipe', 'r'],  // stdin
    1 => ['pipe', 'w'],  // stdout
    2 => ['pipe', 'w'],  // stderr
];

$process = proc_open('./test.sh', $descriptorspec, $pipes, dirname(__FILE__), null);

$stdout = stream_get_contents($pipes[1]);
fclose($pipes[1]);

$stderr = stream_get_contents($pipes[2]);
fclose($pipes[2]);

echo "stdout : \n";
var_dump($stdout);

echo "stderr :\n";
var_dump($stderr);

Output:

When you execute the above PHP script, you will get the following output:

stdout :
string(40) "this is on stdout
this is on stdout too"
stderr :
string(40) "this is on stderr
this is on stderr too"

The output shows the stdout and stderr streams from the test.sh script.