non-graphical 3-way merge tool

Question

I currently use RCS' merge command to do 3-way merges, but one thing has always annoyed me about it. If I use the -A option, the same change made in both files shows up as a conflict:

<<<<<<< file1
file1 line 1
||||||| orig
orig line 1
=======
file2 line 1
>>>>>>> file2
orig line 2
<<<<<<< orig
=======
line added in both changes
>>>>>>> file2
orig line 3

If I use the default (-E) then those identical changes are not shown, but then the ouput only shows the two contributors, not the ancestor, something like this:

<<<<<<< file1
file1 line 1
=======
file2 line 1
>>>>>>> file2
orig line 2
line added in both changes
orig line 3

Is there some program that will essentially do the same behaviour as RCS merge but has some way of showing all three versions in conflicts while automatically merging identical changes?

Answer 1

Try KDiff3.

Answer 2

Looks like diff3 has some interesting options.

On ubuntu:

       -m  --merge
              Output merged file instead of ed script (default -A).

You asked for non-graphical, but vimdiff and gvimdiff can do 3 adjacent windows.

Answer 3

KDiff3 is graphical, but it does have an "--auto" option that, when called from the command line, will perform the merge and show the GUI only if a conflict occurs. I know that means you still need a GUI, but kdiff3 can still be useful from the command line. I use it that way all the time (on Windows - not sure about other versions).

(I wanted to add this comment to the other KDiff3 post, but couldn't work out how to do it - sorry.)