Rebase current branch on
The following command returns the number of commits ahead of
master. That is, how many commits ahead your active branch is.
git rev-list --count HEAD ^master
Then, rebase using the following command, where
N is the number from the previous step. This will open up the editor, where you can choose how to handle individual commits (squash/drop/fixup/etc) and also to edit the commit message. This way all previous commit messages can be organised into the final commit message.
git rebase -i HEAD~N
If, for whatever reason, you want to cancel rebasing and go back, use
git rebase --abort before the rebase is made.