git rebase

SPLITTING COMMITS

In interactive mode, you can mark commits with the
action “edit”. However, this does not necessarily
mean that git rebase expects the result of this
edit to be exactly one commit. Indeed, you can
undo the commit, or you can add other commits.
This can be used to split a commit into two:

• Start an interactive rebase with
  git rebase -i <commit>^, where is the
  commit you want to split. In fact, any commit
  range will do, as long as it contains that commit.
• Mark the commit you want to split with the
  action “edit”.
• When it comes to editing that commit, execute
  git reset HEAD^. The effect is that the HEAD
  is rewound by one, and the index follows suit.
  However, the working tree stays the same.
• Now add the changes to the index that you want
  to have in the first commit. You can use git add
  (possibly interactively) or git gui (or both) to
  do that.
• Commit the now-current index with whatever
  commit message is appropriate now.
• Repeat the last two steps until your working
  tree is clean.
• Continue the rebase with git rebase —continue.