If you've messed up the working tree, but haven't yet committed your
mistake, you can return the entire working tree to the last committed
state with
$ git reset --hard HEAD
If you make a commit that you later wish you hadn't, there are two fundamentally different ways to fix the problem:
-
You can create a new commit that undoes whatever was done by the old
commit. This is the correct thing if your mistake has already been made
public.
-
You can go back and modify the old commit. You should never do this
if you have already made the history public; git does not normally
expect the "history" of a project to change, and cannot correctly
perform repeated merges from a branch that has had its history changed.
Fixing a mistake with a new commit
Creating a new commit that reverts an earlier change is very easy; just pass the git revert command a reference to the bad commit; for example, to revert the most recent commit:
$ git revert HEAD
This will create a new commit which undoes the change in HEAD. You
will be given a chance to edit the commit message for the new commit.
You can also revert an earlier change, for example, the next-to-last:
$ git revert HEAD^
In this case git will attempt to undo the old change while leaving
intact any changes made since then. If more recent changes overlap with
the changes to be reverted, then you will be asked to fix conflicts
manually, just as in the case of <<resolving-a-merge, resolving a
merge>>.