There are plenty of times where I commit something in Git, then realize that I forgot to add one file. It's pretty easy to amend a commit to add those few missed changes, but 99% of the time, I want to keep the commit message the same. Rather than retype the last commit message, or copy/paste it while amending, just use the following command:
git commit --amend -C HEAD
Assuming you've staged the appropriate files you'd like to amend the commit with, this will do the trick. The
-C HEAD portion tells Git that you want to use the comments from the last commit message.
Of course, if you want to edit the commit message, just leave out the
-C HEAD, and after running
git commit --amend, Git will open up your editor and allow you to edit the last commit message instead.