set_time_limit(0);
ignore_user_abort(true);

$lines_limit = 10000000;
$file_src = 'bigfile.txt';

$temp_dir = 'temp_sort_dir/';
$temp_file = $temp_dir.'temp.txt';

if(!file_exists($temp_dir))
	mkdir($temp_dir, 0755) or die("can't make temp direcory");
else
	remove_files($temp_dir);

$f = @fopen($file_src, 'r') or die("can't open source file");

$i = 0;
$arr = array();
while(!feof($f)){
	if($i++ < $lines_limit){
		$arr []= trim(fgets($f, 1024));
	}
	else{
		sort($arr, SORT_NUMERIC);
		file_put_contents($temp_dir. $arr[0]. '.temp', implode("\r\n", $arr)."\r\n");
		$arr = array();
		$i = 0;
	}
}
fclose($f);
unset($arr, $i);

if(!file_exists($temp_file))
	unlink($temp_file);

$files = glob($temp.'*.temp');
foreach($files as $temp_file_i){
	file_put_contents($temp_file, file_get_contents($temp_dir . $temp_file_i), FILE_APPEND);
}
unset($files, $temp_file_i);

if(filesize($temp_file) == filesize($file_src))
	echo copy($temp_file, $file_src) ? 'success' : "can't copy temp file";
else
	echo 'mismatch file sizes';

remove_files($temp_dir);

function remove_files($dir){
	foreach(globe($dir.'*') as $file){
		if(is_file($file))
			unlink($file);
	}
}