recursive directory batch file processing with shell exec

batch-test.php

<?php

// not tested - just for logical demonstration

$path = [
    'source'     => '/source_files/',
    'thumbnails' => '/public_html/images/',
];

function thumbnail_exists($file, $type) {
    global $path;
    // valid types: png, web, watermarked
    $valid_types = ['png', 'web', 'watermarked'];
    
    if (!in_array($type, $valid_types))
        return [false, 'No valid type given'];

    $file = str_replace($path['source'], $path['thumbnail'], $file);

    return file_exists($file);
}

$objects = new RecursiveIteratorIterator(
    new RecursiveDirectoryIterator($path['source']),
    RecursiveIteratorIterator::SELF_FIRST
);

// skip '.' and '..' in unix folders
$objects->setFlags(FilesystemIterator::SKIP_DOTS);

foreach ($objects as $name => $object) {
    if ($object->isFile()) {
        if (strtolower($object->getExtension()) === 'tif') {
            if (!thumbnail_exists($object->getPathname(), 'png')) {
                shell_exec('./convert.sh command_1');
            }
            if (!thumbnail_exists($object->getPathname(), 'web')) {
                shell_exec('./convert.sh command_2');
            }
            if (!thumbnail_exists($object->getPathname(), 'watermarked')) {
                shell_exec('./convert.sh command_3');
            }
        }
    }
}