How Can I Capture Standard Error Output from `exec()` in PHP?

Retrieve Standard Error Stream after Exec() in PHP

Problem:

You're executing a command using PHP's exec() function and want to capture potential error messages written to the standard error stream.

Solution:

PHP provides a more comprehensive approach for controlling and capturing both standard output and error streams using proc_open.

How to Use:

1. Initialize input/output (I/O) descriptor specifications, which define the behavior of standard streams:

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

2. Execute the command using proc_open and provide the descriptor specifications:

$process = proc_open($command, $descriptorspec, $pipes, dirname(__FILE__), null);

3. Read from the standard error pipe using stream_get_contents:

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

Example:

Consider the following script test.sh:

#!/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;

In a PHP script, we can run test.sh and capture stdout and stderr:

$descriptorspec = [0 => ["pipe", "r"], 1 => ["pipe", "w"], 2 => ["pipe", "w"]];
$process = proc_open('./test.sh', $descriptorspec, $pipes);

$stdout = stream_get_contents($pipes[1]);
$stderr = stream_get_contents($pipes[2]);

echo "stdout: $stdout";
echo "stderr: $stderr";

Output:

stdout: this is on stdout
this is on stdout too

stderr: this is on stderr
this is on stderr too

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