Git merge with master without checkout to master

Question

Every time I need to merge develop with master I do:

git checkout master

git merge develop

Sometimes I forget to switch out of master. Due to this, I mistakenly make changes to code while still on master. It can be messy. I've committed to master a few times by mistake.

Is there a way to merge to master without switching first to master?

Answer 1

If you want to do a real merge into master, no. A real merge needs, at least potentially, a work-tree in which to do work. It also uses the index, which needs to match the current branch around the outside of the operation (see git worktree add method below).

If you want to do a fast-forward operation (not an actual merge), it is possible. For instance:

git push . develop:master

(note the lack of + sign or --force option) will attempt to fast-forward your master to the same commit as your develop. Use HEAD to mean the current branch:

git push . HEAD:master

These only work if the fast-forward is possible. If not, you will get an error of the form:

 ! [rejected]              [name] -> master (non-fast-forward)

which tells you that you need a work-tree whose branch is master in which to run git merge.

To do that without changing the branch of your current work-tree, use git worktree add, if your Git is at least 2.5 (preferably at least 2.15). For instance, suppose you are in the top level of your repository, on branch feature/X:

git worktree add ../master   # NB: assumes ../master is available as a directory name
cd ../master
git merge feature/X
...                 # do what it takes to complete the merge here

cd -                # return to your main repository
rm -rf ../master    # remove added worktree
git worktree prune  # clean up list of added worktrees

The added work-tree has its own index (and its own HEAD) so git merge now has an index and work-tree in which to do its job, or leave its mess for you to fix, whichever actually occurs (see kostix's comment).