PHP script that would guess the type of a file using its metadata and would rename it. Often times this is caused by unsafe removal of USB media off the USB slot.

recover_lost_filename.php

<?php

$folder = __DIR__ .'/FOUND.000';

$dir = new DirectoryIterator($folder);

$map = array(
    'application/vnd.ms-excel' => 'xls',
    'application/msword' => 'doc',
    'application/zip' => 'zip',
    'image/jpeg' => 'jpg',
//    'audio/mpeg' => 'mpeg',
);

foreach ($dir as $fileinfo) {
    printf('Processing %s:', $fileinfo->getFilename());

    if ($fileinfo->isDot()) {
        printf(" IGNORED\n");
        continue;
    }

    if ($fileinfo->getExtension() !== 'CHK') {
        printf(" IGNORED\n\n");
        continue;
    }

    printf(" OK\n");

    $mimeType = mime_content_type($fileinfo->getRealPath());

    printf("Content-type: %s\n", $mimeType);

    if (!array_key_exists($mimeType, $map)) {
        printf("Extension: UNKNOWN\n\n");
        continue;
    }

    $extension = $map[$mimeType];

    $newFilename = $fileinfo->getBasename() .'.'. $extension;

    printf("New file name: %s\n", $fileinfo->getPath() .'/'. $newFilename);

    rename($fileinfo->getRealPath(), $fileinfo->getPath() .'/'. $newFilename);

    echo "\n";
}