diff compares files line by line, here we just redirect the output of cmd1 and cmd2 via <, so they serve as 'proxies' for the file-args diff expects you might

diff compares files line by line, here we just redirect the output of cmd1 and cmd2 via <, so they serve as 'proxies' for the file-args diff expects you might want to read into redirection on the commandline, it's amazingly powerful