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+Date: Sat, 13 Aug 2005 22:16:02 -0700 (PDT)
+From: Linus Torvalds <torvalds@osdl.org>
+To: Steve French <smfrench@austin.rr.com>
+cc: git@vger.kernel.org
+Subject: Re: sending changesets from the middle of a git tree
+Abstract: In this article, Linus demonstrates how a broken commit
+ in a sequence of commits can be removed by rewinding the head and
+ reapplying selected changes.
+
+On Sat, 13 Aug 2005, Linus Torvalds wrote:
+
+> That's correct. Same things apply: you can move a patch over, and create a
+> new one with a modified comment, but basically the _old_ commit will be
+> immutable.
+
+Let me clarify.
+
+You can entirely _drop_ old branches, so commits may be immutable, but
+nothing forces you to keep them. Of course, when you drop a commit, you'll
+always end up dropping all the commits that depended on it, and if you
+actually got somebody else to pull that commit you can't drop it from
+_their_ repository, but undoing things is not impossible.
+
+For example, let's say that you've made a mess of things: you've committed
+three commits "old->a->b->c", and you notice that "a" was broken, but you
+want to save "b" and "c". What you can do is
+
+ # Create a branch "broken" that is the current code
+ # for reference
+ git branch broken
+
+ # Reset the main branch to three parents back: this
+ # effectively undoes the three top commits
+ git reset HEAD^^^
+ git checkout -f
+
+ # Check the result visually to make sure you know what's
+ # going on
+ gitk --all
+
+ # Re-apply the two top ones from "broken"
+ #
+ # First "parent of broken" (aka b):
+ git-diff-tree -p broken^ | git-apply --index
+ git commit --reedit=broken^
+
+ # Then "top of broken" (aka c):
+ git-diff-tree -p broken | git-apply --index
+ git commit --reedit=broken
+
+and you've now re-applied (and possibly edited the comments) the two
+commits b/c, and commit "a" is basically gone (it still exists in the
+"broken" branch, of course).
+
+Finally, check out the end result again:
+
+ # Look at the new commit history
+ gitk --all
+
+to see that everything looks sensible.
+
+And then, you can just remove the broken branch if you decide you really
+don't want it:
+
+ # remove 'broken' branch
+ git branch -d broken
+
+ # Prune old objects if you're really really sure
+ git prune
+
+And yeah, I'm sure there are other ways of doing this. And as usual, the
+above is totally untested, and I just wrote it down in this email, so if
+I've done something wrong, you'll have to figure it out on your own ;)
+
+ Linus
+-
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