Question

After making a few changes to branch master I decided to work from a new branch. I did git checkout -b new_branch_name and a new branch was created and checked out. git status showed the changes I had made to master.

I was curious if my changes were now on both branches (master and new_branch_name) or just new_branch_name. So I checked out master and noticed my changes were there as well. So I reverted those changes with git checkout -- fileThatChanged. The changes were indeed gone from master.

Unfortunately checking out new_branch_name and running git status showed my changes were reverted from that branch as well.

I’d like to understand what happened and how can I avoid this in the future.

One solution is to just create/checkout a new branch before starting work.

Answer 1

You had never committed your changes to either branch. That is, if you did this:

$ git status

And saw something like this:

# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   myfile.txt
#

The changes to “myfile.txt” do not “exist” on any branch — they are only in your local working copy. They don’t end up on a branch until you have comitted them to a repository.

If at this point I were to type:

$ git checkout myfile.txt

This would obliterate my changes (and return the file to whatever it looked like in the last commit on my current branch).

If I wanted to commit these changes on a new branch, I might do something like this:

$ git checkout -b new_branch_name
$ git add myfile.txt
$ git commit -m "made some changes"