Depends on you definition of "simple". Here are 5 commands that gets the job done in a (IMHO) conceptually simple way.
Use
git checkout -b [tmpBranch] [fromBranch]
to create (and checkout) a _new_ branch pointing to the same commit as the "from"-branch. Then use
git rebase --onto [toBranch] [fromBranchStart] [tmpBranch]
to rebase all commits between [fromBranchStart] and [fromBranch] on top of [toBranch]. Since this was done with HEAD == [tmpBranch], the original [fromBranch] is not moved, and therefore *still* points to the old commits. [tmpBranch], however, have been moved to point at the rebased commits. This in effect *copies* the commits from [fromBranch] to [tmpBranch]. Now, all that remains is to reconcile [tmpBranch] and [toBranch], and finally remove [tmpBranch]:
git checkout [toBranch]
git merge [tmpBranch]
git branch -d [tmpBranch]
The merge should be a simple fast-forward without any conflicts.
Here is an illustrated version of what's going on:
Initial layout:
G---H---I <---- [fromBranch]
/
A---B---C---D---E---F <-- [toBranch]
^----------------- [fromBranchStart]
git checkout -b [tmpBranch] [fromBranch]
G---H---I <---- [fromBranch]
/ ^------- [tmpBranch]
A---B---C---D---E---F <-- [toBranch]
^----------------- [fromBranchStart]
git rebase --onto [toBranch] [fromBranchStart] [tmpBranch]
G---H---I <------------------- [fromBranch]
/
A---B---C---D---E---F---G'---H'---I' <-- [tmpBranch]
^ ^-------------------- [toBranch]
--------------------------------- [fromBranchStart]
git checkout [toBranch]
git merge [tmpBranch]
git branch -d [tmpBranch]
G---H---I <------------------- [fromBranch]
/
A---B---C---D---E---F---G'---H'---I' <-- [toBranch]
^-------------------------------- [fromBranchStart]
This should also work even if your commit graphs are considerably more complicated.
If you need to drop/edit/squash any commits between [fromBranchStart] and [fromBranch], simply add a "--interactive" to the rebase command.
Have fun!
...Johan
--
Johan Herland, <johan@herland.net>
www.herland.net
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