Do you want to compare the repositories of 27+ students to catch if one of them is cheating?

compare.php

<?php
$dirs = array_slice(scandir('.'), 2);

for($i=0;$i<count($dirs);$i++){
	if ( is_dir($dirs[$i]) ){
		$base = $dirs[$i];
		for($j=0;$j<count($dirs);$j++){
			if ($i!=$j) {
				if ( is_dir($dirs[$j]) ){
					$against = $dirs[$j];
					$data = `wdiff -s123 "$base/css/main.css" "$against/css/main.css"`;
					$lines = explode("\n", $data);
					$tokens = explode(" ", $lines[0]);
					$change = (int)substr($tokens[count($tokens)-2], 0,-1);
					if($change < 40 ) {
						echo $lines[0];
						echo "\n";
						echo $lines[1];
						echo "\n\n";
					}
				}
			}
		}
	}
}