How do I merge multiple branches into master?

        C---D  =>b1
      /    
     /  E---F  =>b2
     | /   
  A--B =======> master
     | \
     \  G---H  =>b3
      \ 
       I---J   =>b4

I want to merge b1,b2,b3,b4 into master, is it possible merge at once?

something like:

git checkout master
git merge b1 b2 b3 b4

Solution 1:

Git's merge command supports multiple merging strategies. There are two strategies that can merge more than two branches at a time.

See also this question for a less formal description of each one.

octopus

This resolves cases with more than two heads, but refuses to do a complex merge that needs manual resolution. It is primarily meant to be used for bundling topic branch heads together. This is the default merge strategy when pulling or merging more than one branch.

The last statement implies that if you do git merge branch1 branch2 ..., it'll use the octopus strategy.

ours

This resolves any number of heads, but the resulting tree of the merge is always that of the current branch head, effectively ignoring all changes from all other branches. It is meant to be used to supersede old development history of side branches.

See this question for a use case example.

Solution 2:

Git has a merging strategy called octupus which can merge multiple branches, as long as there are no complex conflicts. The command to do this is exactly as you suggested git merge b1 b2.