Unable to diff files in two separate branches in Git

Question

I have FileA in branchA and FileB in branchB.

The problem is that I can access only one file at time. I would like to be able to compare the files by FileMerge or meld, since they are the only diffTools whichI have found for Mac.

How can you diff by meld/FileMerge the two files?

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[Solved]: 1st developed Problem: FileMerge does not allow standard input

Masi: You can use opendiff to allow FileMerge to have files from standard input. So the next problem is to find how to make git's diff tool to use opendiff.

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2nd developed Problem: to make Git's diff tool to use opendiff in Mac

Answer 1

You can use "git mergetool" for merging, and in modern git (meaning version 1.6.3 and later) "git difftool" for comparing using graphical tools. Of course you would have to configure them first, but they do some autodetection (with some hardcoded preference, of course), and if I remember correctly opendiff support is built in.

And then of course you would be able to use your graphical tool (opendiff / FileMerge) as you would use ordinary "git diff", for example

prompt> git difftool somebranch:UNREADME otherbranch:README 

Answer 2

git supports branch names as part of the repository paths. Eg if you have the following files in your repository, README only on master, and UNREADME only on branch:

master:README  branch:UNREADME 

You can diff them via git with:

git diff branch:UNREADME master:README 

You can get a repository artifact to standard output with git show:

git show branch1:UNREADME 

So if your external diff utility can take 2 files on the bash prompt, you can diff them with something like:

diff-command <(git show branch1:UNREADME) <(git show master:README) 

Where the <(...) bash syntax takes the output of the enclosed command, runs it in a pipe and places the file path of the pipe on the command line.