From master, commit to another branch

Question

I usually create branches for the different segments of code but once in a while I forget to create a new branch and everything is happening on the master branch.

How can I say to git that although I am on the master branch, this commit is for the xyz branch?

Answer 1

Just checkout that branch first and commit to it

git checkout -b mynewbranch
# `git add` what you need
git commit -m "my commit message"

Answer 2

If you already committed on master one which should go on another branch, you can;

# create a branch on that commit
git branch mynewbranch
# reset master to the previous commit
# git reset --hard HEAD~

(Make sure you don't have any private file not added yet to the index, or the reset --hard would erase them: you can use git stash to save them temporarily)

Then you can switch on mynewbranch is you have other commits to do on that new branch:

git checkout mynewbranch