如何在此PHP脚本的末尾添加文本

Question

这是正常的脚本。它将数据保存到文件中。

       <?php
if (isset($_GET['field'])) {
$file = 'data.txt';
// Open the file to get existing content
$current = file_get_contents($file);

// Append a new line to the file
$current .= "\n".$_GET['field'];

// Write the contents back to the file
file_put_contents($file, $current);
}
?>

但是我希望它在发送的内容中添加（由用户添加）。我试过这个：

     <?php
if (isset($_GET['field'])) {
$file = 'data.txt';
// Open the file to get existing content
$current = file_get_contents($file);

// Append a new line to the file
$current .= "\n".$_GET['field'] + "(added by a user)";

// Write the contents back to the file
file_put_contents($file, $current);
}
?>

但它不起作用。我该怎么做？