git rebase --interactive

gistfile1.txt

# oh no...

~/some-git-repo$ git log --oneline
d28077cbfb16 (HEAD -> master) even more changes
7911a300794f more changes
7ede0b52d6eb fixed stuff
b554432cd465 this should never have been committed
532e5d734387 Initial commit

# You committed something bad, and it's not your latest commit either!
# The later changes don't depend on it, so you could easily revert it:

~/some-git-repo$ git revert b554432cd465
[master 4a21e5c437ee] Revert "this should never have been committed"
 1 file changed, 2 deletions(-)

# But this would leave a permanent record of your mistake:

~/some-git-repo$ git log --oneline
4a21e5c437ee (HEAD -> master) Revert "this should never have been committed"
d28077cbfb16 even more changes
7911a300794f more changes
7ede0b52d6eb fixed stuff
b554432cd465 this should never have been committed
532e5d734387 Initial commit

# You haven't pushed any of this yet (or noone is downstream), so surely
# there must be a way to fix it?
#
# git rebase --interactive (-i for short) to the rescue!
#
# The argument to pass to git rebase -i is the commit *before* the
# commit(s) you want to undo or edit, which can e.g. be described as
#	HEAD^^^^	four commits ago (assuming you didn't revert yet)
#       HEAD@{4}        same thing
#	b554432cd465^	commit before the wrong one
#	532e5d734387	last good commit

~/some-git-repo$ git rebase -i b554432cd465^
# ... a text editor opens ...
#
# Change the keyword before the bad commit from "pick" to "drop":
drop b554432cd465 this should never have been committed
pick 7ede0b52d6eb fixed stuff
pick 7911a300794f more changes
pick d28077cbfb16 even more changes
#
# Save and exit.

~/some-git-repo$ git rebase -i b554432cd465^
Successfully rebased and updated refs/heads/master.

# We did it?

~/some-git-repo$ git log --oneline
1e1950143c7c (HEAD -> master) even more changes
bb079301b686 more changes
1546fdf7d427 fixed stuff
532e5d734387 Initial commit

# Yay \o/

# Note that since you're rewritten history, all later commits have
# a different id than before.  If you pushed the mistake then you
# will need to use --force to push this rewrite.  Don't push history
# rewrites if anyone is downstream (unless you hate them and there
# aren't enough people downstream to form a lynch mob...)
#
# See also http://justinhileman.info/article/git-pretty/