For a long time, I didn’t know a way to do directory comparison using git difftool command, extdiff extension from Mercurial did perform much more superior than Git.
Though it may be a bit out of date, I just found that after v1.7.11, Git now supports directory comparison through --dir-diff option, fantastic!
UPDATE 12/11/2012: You will need v1.8.0 version of msysgit installed, as noted by Scooter Software (Reference).
So here is a list of steps for me to make Beyond Compare 3 and Git directory comparison work under Windows.
First of all, Execute following commands in the Git Bash shell (or just modify your .gitconfig directly). You may need to change the folder where BCompare.exe resides.
git config --global diff.tool bc3
git config --global difftool.bc3.cmd "\"c:/Program Files/Beyond Compare 3/BCompare.exe\" \"$LOCAL\" \"$REMOTE\""
git config --global difftool.prompt false
NOTE: Instead of bcomp.exe, use BCompare.exe, because I’ve found bcomp.exe returns too early, which will cause errors like this:
...Git/libexec/git-core\git-difftool line 444: Bad file number
Then make an alias for difftool:
git config --global alias.dt "difftool --dir-diff"
Now, you can use git dt to open Beyond Compare 3 for directory comparison in git repositories.