Question

Can you undo a past commit, that has long been merged into your git repository, via a git command? Or do you have to manually undo all the changes made in that commit?

Answer 1

You can always just revert the changes from a single commit by doing:

git revert <commit-id>

note that this creates a new commit, undoing just those changes

E.g. git log --oneline

d806fc9 two
18cdfa2 bye
62c332e hello
c7811ee initial

Say I want to revert changes in commit 18cdfa2:

git revert 18cdfa2

We now have: git log -1 -p

commit fb9d6627a71636503fc9a1eb4f725937c783ecee
Author: Seth <sehe@mint12.(none)>
Date:   Wed Oct 3 10:32:46 2012 +0200

    Revert "bye"

    This reverts commit 18cdfa27c964b66b624be1030250757b745d6866.

diff --git a/a b/a
index 0907563..3b18e51 100644
--- a/a
+++ b/a
@@ -1 +1 @@
-bye world
+hello world