Stream a file that is being written to by another process

stream.php

<?php

/**
 * This script streams a file that is being written to by another process.
 * It will continue fread()ing past EOF until explicitly stopped with CTRL+C.
 *
 * The script will exit with a status code of 0 if and only if the stream is stopped *after* EOF has been reached,
 * i.e. if actual EOF *MAY* have been reached.
 *
 * The output of the streamed file is sent to STDOUT, and the output of the script is sent to STDERR,
 * so the output can be piped to another program while watching progress in the terminal.
 */

declare(strict_types=1);
declare(ticks=1);

if (!extension_loaded('pcntl')) {
    fwrite(STDERR, 'The pcntl extension is required.');
    exit(1);
}

$interrupted = false;

pcntl_signal(SIGINT, function () use (&$interrupted): void {
    $interrupted = true;
});

if ($argc !== 2) {
    fwrite(STDERR, sprintf("Usage: %s <file>\n", $argv[0]));
    exit(1);
}

$filename = $argv[1];

$fp = @fopen($filename, 'rb');

if ($fp === false) {
    fwrite(STDERR, sprintf("Could not open file '%s' for reading\n", $filename));
    exit(1);
}

$totalBytes = 0;
$totalBytesSinceEof = 0;

$lastRead = null;
$eof = false;

while (true) {
    $eof = $eof || feof($fp);
    $data = @fread($fp, 1024 * 1024);

    if ($data === false) {
        fwrite(STDERR, sprintf("Could not read from file '%s'\n", $filename));
        exit(1);
    }

    $bytes = strlen($data);
    $totalBytes += $bytes;

    if ($eof) {
        $totalBytesSinceEof += $bytes;
    }

    if ($bytes !== 0) {
        $lastRead = time();
    }

    fwrite(STDOUT, $data);

    fwrite(STDERR, "\r\033[K"); // clear line
    fwrite(STDERR, sprintf('%s bytes read', number_format((float) $totalBytes)));

    if ($eof) {
        fwrite(STDERR, sprintf(', %s bytes since EOF', number_format((float) $totalBytesSinceEof)));

        if ($lastRead !== null) {
            fwrite(STDERR, sprintf(', last read %s seconds ago', time() - $lastRead));
        }
    }

    if ($interrupted) {
        break;
    }

    if ($bytes === 0) {
        usleep(100000);
    }
}

exit($eof ? 0 : 1);