How to modify a specified commit?

Question

I usually submit a list of commits for review. If I have the following commits:

1. HEAD
2. Commit3
3. Commit2
4. Commit1

...I know that I can modify head commit with git commit --amend. But how can I modify Commit1, given that it is not the HEAD commit?

Answer 1

Came to this approach (and it is probably exactly the same as using interactive rebase) but for me it's kind of straightforward.

Note: I present this approach for the sake of illustration of what you can do rather than an everyday alternative. Since it has many steps (and possibly some caveats.)

Say you want to change commit 0 and you are currently on feature-branch

some-commit---0---1---2---(feature-branch)HEAD

Checkout to this commit and create a quick-branch. You can also clone your feature branch as a recovery point (before starting).

?(git checkout -b feature-branch-backup)
git checkout 0
git checkout -b quick-branch

You will now have something like this:

0(quick-branch)HEAD---1---2---(feature-branch)

Stage changes, stash everything else.

git add ./example.txt
git stash

Commit changes and checkout back to feature-branch

git commit --amend
git checkout feature-branch

You will now have something like this:

some-commit---0---1---2---(feature-branch)HEAD
           \
             ---0'(quick-branch)

Rebase feature-branch onto quick-branch (resolve any conflicts along the way). Apply stash and remove quick-branch.

git rebase quick-branch
git stash pop
git branch -D quick-branch

And you end up with:

some-commit---0'---1'---2'---HEAD(feature-branch)

Git will not duplicate (although I can't really say to what extent) the 0 commit when rebasing.

Note: all commit hashes are changed starting from the commit we originally intended to change.

Answer 2

Automated interactive rebase edit followed by commit revert ready for a do-over

I found myself fixing a past commit frequently enough that I wrote a script for it.

Here's the workflow:

1. git commit-edit <commit-hash>
   

   This will drop you at the commit you want to edit.

2. Fix and stage the commit as you wish it had been in the first place.

   (You may want to use git stash save to keep any files you're not committing)

3. Redo the commit with --amend, eg:

   git commit --amend
   

4. Complete the rebase:

   git rebase --continue
   

For the above to work, put the below script into an executable file called git-commit-edit somewhere in your $PATH:

#!/bin/bash

set -euo pipefail

script_name=${0##*/}

warn () { printf '%s: %s\n' "$script_name" "$*" >&2; }
die () { warn "$@"; exit 1; }

[[ $# -ge 2 ]] && die "Expected single commit to edit. Defaults to HEAD~"

# Default to editing the parent of the most recent commit
# The most recent commit can be edited with `git commit --amend`
commit=$(git rev-parse --short "${1:-HEAD~}")
message=$(git log -1 --format='%h %s' "$commit")

if [[ $OSTYPE =~ ^darwin ]]; then
  sed_inplace=(sed -Ei "")
else
  sed_inplace=(sed -Ei)
fi

export GIT_SEQUENCE_EDITOR="${sed_inplace[*]} "' "s/^pick ('"$commit"' .*)/edit \\1/"'
git rebase --quiet --interactive --autostash --autosquash "$commit"~
git reset --quiet @~ "$(git rev-parse --show-toplevel)"  # Reset the cache of the toplevel directory to the previous commit
git commit --quiet --amend --no-edit --allow-empty  #  Commit an empty commit so that that cache diffs are un-reversed

echo
echo "Editing commit: $message" >&2
echo

Answer 3

Based on Documentation

Amending the message of older or multiple commit messages

git rebase -i HEAD~3 

The above displays a list of the last 3 commits on the current branch, change 3 to something else if you want more. The list will look similar to the following:

pick e499d89 Delete CNAME
pick 0c39034 Better README
pick f7fde4a Change the commit message but push the same commit.

Replace pick with reword before each commit message you want to change. Let say you change the second commit in the list, your file will look like the following:

pick e499d89 Delete CNAME
reword 0c39034 Better README
pick f7fde4a Change the commit message but push the same commit.

Save and close the commit list file, this will pop up a new editer for you to change your commit message, change the commit message and save.

Finaly Force-push the amended commits.

git push --force

Answer 4

You can use git rebase, for example, if you want to modify back to commit bbc643cd, run

$ git rebase --interactive 'bbc643cd^'

In the default editor, modify pick to edit in the line whose commit you want to modify. Make your changes and then commit them with the same message you had before:

$ git commit --all --amend --no-edit

to modify the commit, and after that

$ git rebase --continue

to return back to the previous head commit.

WARNING: Note that this will change the SHA-1 of that commit as well as all children -- in other words, this rewrites the history from that point forward. You can break repos doing this if you push using the command git push --force

Answer 5

Interactive rebase with --autosquash is something I frequently use when I need to fixup previous commits deeper in the history. It essentially speeds up the process that ZelluX's answer illustrates, and is especially handy when you have more than one commit you need to edit.

From the documentation:

--autosquash

When the commit log message begins with "squash! …​" (or "fixup! …​"), and there is a commit whose title begins with the same …​, automatically modify the todo list of rebase -i so that the commit marked for squashing comes right after the commit to be modified

Assume you have a history that looks like this:

$ git log --graph --oneline
* b42d293 Commit3
* e8adec4 Commit2
* faaf19f Commit1

and you have changes that you want to amend to Commit2 then commit your changes using

$ git commit -m "fixup! Commit2"

alternatively you can use the commit-sha instead of the commit message, so "fixup! e8adec4 or even just a prefix of the commit message.

Then initiate an interactive rebase on the commit before

$ git rebase e8adec4^ -i --autosquash

your editor will open with the commits already correctly ordered

pick e8adec4 Commit2
fixup 54e1a99 fixup! Commit2
pick b42d293 Commit3

all you need to do is save and exit

Answer 6

Completely non-interactive command⁽¹⁾

I just thought I'd share an alias that I'm using for this. It's based on non-interactive interactive rebase. To add it to your git, run this command (explanation given below):

git config --global alias.amend-to '!f() { SHA=`git rev-parse "$1"`; git commit --fixup "$SHA" && GIT_SEQUENCE_EDITOR=true git rebase --interactive --autosquash "$SHA^"; }; f'

The biggest advantage of this command is the fact that it's no-vim.

---

⁽¹⁾given that there are no conflicts during rebase, of course

Usage

git amend-to <REV> # e.g.
git amend-to HEAD~1
git amend-to aaaa1111

The name amend-to seems appropriate IMHO. Compare the flow with --amend:

git add . && git commit --amend --no-edit
# vs
git add . && git amend-to <REV>

Explanation

• git config --global alias.<NAME> '!<COMMAND>' - creates a global git alias named <NAME> that will execute non-git command <COMMAND>
• f() { <BODY> }; f - an "anonymous" bash function.
• SHA=`git rev-parse "$1"`; - converts the argument to git revision, and assigns the result to variable SHA
• git commit --fixup "$SHA" - fixup-commit for SHA. See git-commit docs
• GIT_SEQUENCE_EDITOR=true git rebase --interactive --autosquash "$SHA^"
  • git rebase --interactive "$SHA^" part has been covered by other answers.
  • --autosquash is what's used in conjunction with git commit --fixup, see git-rebase docs for more info
  • GIT_SEQUENCE_EDITOR=true is what makes the whole thing non-interactive. This hack I learned from this blog post.