Use the following to configure git to use diffmerge for diffing and merging files:
git config --global diff.tool diffmerge
git config --global difftool.diffmerge.cmd "diffmerge "$LOCAL" "$REMOTE""
git config --global merge.tool diffmerge
git config --global mergetool.diffmerge.cmd "diffmerge --merge --result="$MERGED"
"$LOCAL" "$BASE" "$REMOTE""
git config --global mergetool.diffmerge.trustexitcode false
The following will show diffmerge with the two versions of myfile.java side by side:
git difftool master~2 myfile.java