Search Google for quines. Here's the Wikipedia article.

Update: The key to understand how your program works is the printf documentation. Here's the content of the $body variable:

$body = %c%s%c;
printf($body,34,$body,34);
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And now let's see what the printf invocation below does:

printf($body,34,$body,34);
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The first argument, $body, is the format string. The following arguments, 34, $body, 34 will be interpolated according to format conventions. Second and fourth arguments (34 and 34) are treated as ascii character codes and the corresponding character, double-quotes, will be interpolated in the place of %c's. Third argument of printf will be interpolated as a string in the place of the %s. Therefore, the output will be equivalent to the concatenation of the following strings:

'
$body = ' . chr(34) . $body . chr(34) . ';
printf($body,34,$body,34);
'
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Try printing that and you'll see