git diff side by side

https://stackoverflow.com/questions/7669963/how-can-i-get-a-side-by-side-diff-when-i-do-git-diff
git difftool -y

submodule

clone with submodule
With version 2.13 of Git and later, --recurse-submodules can be used instead of --recursive:

git clone --recurse-submodules -j8 git://github.com/foo/bar.git
cd bar

Editor’s note: -j8 is an optional performance optimization that became available in version 2.8, and fetches up to 8 submodules at a time in parallel — see man git-clone.

With version 1.9 of Git up until version 2.12 (-j flag only available in version 2.8+):

git clone --recursive -j8 git://github.com/foo/bar.git
cd bar

With version 1.6.5 of Git and later, you can use:

git clone --recursive git://github.com/foo/bar.git
cd bar

For already cloned repos, or older Git versions, use:

git clone git://github.com/foo/bar.git
cd bar
git submodule update --init --recursive

copy file while preserve history

All you have to do is:

1. move the file to two different locations,
2. merge the two commits that do the above, and
3. move one copy back to the original location.

You will be able to see historical attributions (using git blame) and full history of changes (using git log) for both files.

Suppose you want to create a copy of file foo called bar. In that case the workflow you'd use would look like this:

git mv foo bar
git commit

SAVED=`git rev-parse HEAD`
git reset --hard HEAD^
git mv foo copy
git commit

git merge $SAVED     # This will generate conflicts
git commit -a        # Trivially resolved like this

git mv copy foo
git commit