Git: How to modify a commit shared with multiple branches

Question

I have the following tree:

branch1               G---H---I
                     /   
master       A---B---C---D---E---F
                          \
branch2                    M---N---O

I need to make some modifications in B. Is there any easy way to spread the modifications to all the branches (master, branch1 and branch2) ?

Answer 1

The safest way to do this is:

1. Create a new branch from B

   git checkout -b BPRIME SHA_OF_B

2. Make some changes, and commit them. you're graph will look like:

   BPRIME              B'
                      /  
   branch1           /   G---H---I
                    /   /   
   master       A---B---C---D---E---F
                             \
   branch2                    M---N---O
   

3. Then cherry pick the commits from BPRIME to each of the branches.

   $ git checkout branch1 && git cherry-pick B'
   $ git checkout master && git cherry-pick B'
   $ git checkout branch2 && git cherry-pick B'
   

This is the safest option because you are not changing the history.

Answer 2

Make the new commit in master branch and then rebase the other branches with the master.