non verbose way to send output to stderr or stdout

stdLog.php

<?php declare(strict_types=1);
/**
 * Writes messages to stderr or stdout.
 *
 * @author Sébastien Monterisi <https://gist.github.com/SebSept/>
 * @throws FailureToWriteToFile
 */

function stdErr(string $message): void { stdLog('php://stderr', $message); }
function stdOut(string $message): void { stdLog('php://stdout', $message); }

function stdLog(string $stream_path, string $message): void
{
    if (!file_put_contents($stream_path, $message.PHP_EOL)) {
        throw new \FailureToWriteToFile($stream_path);
    }
}

class FailureToWriteToFile extends Exception
{
}

usage.php

<?php
/**
 * Usage
 *
 * `php usage.php 1>log.txt 2>errors.txt`
 *
 * log.txt    contains "sortie normale"
 * errors.txt contains "vers erreur"
 *
 * ---
 *
 * `php usage.php > log.txt`
 *
 * log.txt    contains "sortie normale"
 * stderr messages are printed
 */

require_once "stdLog.php";

stdErr("vers erreur");
stdOut("sortie normale");

Better use core defined constants STDOUT and STDERR;