How to format a DateTime object as a Unix timestamp in PHP?

To format a DateTime object as a Unix timestamp in PHP, you can use the format() function and the U format specifier.

Here's an example:

$dateTime = new DateTime();
$unixTimestamp = $dateTime->format('U');
echo $unixTimestamp;

In this example, $dateTime is a DateTime object representing the current date and time. The format('U') method call formats the DateTime object as a Unix timestamp. Finally, the Unix timestamp is echoed to the output.