Is there an option in emacs like vimdiff?

Question

I simply want to supply two files to emacs from terminal and it should open them in two separate windows in diff mode.

Answer 1

You're looking for ediff. In emacs you can activate it via M-x ediff and the file names. To call it from commandline try something like this (taken from emacs wiki):

(defun command-line-diff (switch)
  (let ((file1 (pop command-line-args-left))
        (file2 (pop command-line-args-left)))
    (ediff file1 file2)))

(add-to-list 'command-switch-alist '("diff" . command-line-diff))

;; Usage: emacs -diff file1 file2

To get you started here are a few additional "saner" defaults"

;; saner ediff default
(setq ediff-diff-options "-w")
(setq ediff-split-window-function 'split-window-horizontally)
(setq ediff-window-setup-function 'ediff-setup-windows-plain)

These will always split to have ediff windows side-by-side.

If you want to always force a new frame (it is cleaner this way), try these additionally:

(add-hook 'ediff-before-setup-hook 'new-frame)
(add-hook 'ediff-quit-hook 'delete-frame)

I hope that helps for the beginning.