index.php

<?php
require('vendor/autoload.php');
// this will simply read AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY from env vars
$s3 = new Aws\S3\S3Client([
    'version'  => '2006-03-01',
    'region'   => 'us-east-1',
]);
$bucket = getenv('S3_BUCKET')?: die('No "S3_BUCKET" config var in found in env!');
?>
<html>
    <head><meta charset="UTF-8"></head>
    <body>
        <h1>S3 upload example</h1>
<?php
if($_SERVER['REQUEST_METHOD'] == 'POST' && isset($_FILES['userfile']) && $_FILES['userfile']['error'] == UPLOAD_ERR_OK && is_uploaded_file($_FILES['userfile']['tmp_name'])) {
    // FIXME: you should add more of your own validation here, e.g. using ext/fileinfo
    try {
        // FIXME: you should not use 'name' for the upload, since that's the original filename from the user's computer - generate a random filename that you then store in your database, or similar
        $upload = $s3->upload($bucket, $_FILES['userfile']['name'], fopen($_FILES['userfile']['tmp_name'], 'rb'), 'public-read');
?>
        <p>Upload <a href="<?=htmlspecialchars($upload->get('ObjectURL'))?>">successful</a> :)</p>
<?php } catch(Exception $e) { ?>
        <p>Upload error :(</p>
<?php } } ?>
        <h2>Upload a file</h2>
        <form enctype="multipart/form-data" action="<?=$_SERVER['PHP_SELF']?>" method="POST">
            <input name="userfile" type="file"><input type="submit" value="Upload">
        </form>
    </body>
</html>