vimdiff  - edit two, three or four versions of a file with Vim and show differences

$ cat a.txt
this is line 1
this is line 2
this is line 3
this is line 4

$ cat b.txt
this is line 1
this is line 2
this is line 3
this is line 5
this is line 6

$ vimdiff a.txt b.txt

To split the screen horizontally
$ vimdiff -o a.txt b.txt

To apply changes from the left file to the right file
:diffput

To apply changes from the right file to the left file
:diffget

To undo changes
:diffupdate

To exit the diff window
:qa to exit all the files without saving.
:q to exit the files one by one without saving.
:wq! to save and exit files one by one.



regards,
T.Dhanasekar