php reads file content and clears file

//Read file content
$fh = fopen($path, "r+");
if( flock($ fh, lock_ex) ){//Add write lock
$old_content=json_decode(fread($fh,filesize($path)),true);
$old_content=$old_content.$new_content ;
ftruncate($fh,0); // Truncate the file to the given length
rewind($fh); // Rewind the position of the file pointer
fwrite($fh,json_encode($old_content));
/ / @chmod($path,0644);
flock($fh, lock_un); //Unlock
}
fclose($fh);