History and undoing

Every commit you make is kept, with its author, its date and the message you wrote. git log is how you read that history. Without options, it lists the commits newest first, and shows each one’s full hash, author, date and message. For a long history that is a lot of text, so a few options help:

• --oneline prints one line per commit: the short hash and the message.
• -n 2 shows only the newest two commits. Any number works; -n 1 shows just the newest.
• --stat adds which files each commit changed, and by how much.
• A file name at the end, as in git log pancakes.md, lists only the commits that changed that file.

Options combine freely: git log --oneline -n 5 shows the newest five commits, one line each.

Every session on this page starts from the recipes repository as Module 2’s main example left it, with three commits. Your own repository may hold a few more, if you also committed a .gitignore or did the exercises, and your hashes are different, because Git calculates them from the time of each commit as well as its content. Always use the hashes your own git log prints. Your repository also grows as you work through this module, so your output may differ from the pages in small ways; the commands work the same.

git log --oneline

1ad5842 Say what the notes are for
8bf3c2d Add a pancake recipe
907a979 Add a README

git log -n 1

commit 1ad584283c1471035cb8e8538e2ea2cc2ce54824
Author: Alex Smith <alex@example.com>
Date:   Mon Jan 5 09:09:00 2026 +0000

    Say what the notes are for

git log --oneline --stat

1ad5842 Say what the notes are for
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
8bf3c2d Add a pancake recipe
 pancakes.md | 5 +++++
 1 file changed, 5 insertions(+)
907a979 Add a README
 README.md | 3 +++
 1 file changed, 3 insertions(+)

git log --oneline pancakes.md

8bf3c2d Add a pancake recipe

git log -n 1 shows the newest commit in full: its 40-character hash, the author, the date and the message. With --stat, each commit gets a short summary of its changes. README.md | 2 +- says that the commit changed two lines of README.md: one added (+) and one removed (-), which is how Git records a line that was reworded. pancakes.md | 5 +++++ says that five lines were added.

The last command, git log --oneline pancakes.md, lists only 8bf3c2d Add a pancake recipe, because no other commit touched pancakes.md. When you want to know when, and why, a file changed, this is the place to start.

git log tells you which commits exist. Three related commands show what actually changed:

• git diff compares the working tree with the staging area. It shows the changes you have made but not yet staged.
• git diff --staged compares the staging area with the last commit. It shows what your next commit will contain. (--cached is another name for the same option.)
• git show shows one commit: its hash, author, date and message, followed by its changes. On its own it shows the newest commit; give it a hash to see another one.

git status tells you which files changed; these commands show you how, so you can check every change before it goes into the history. In the session, you change the pancake recipe to use less milk and add a pinch of salt, then follow the change from the working tree into a commit.

# Pancakes

- 200 g flour
- 2 eggs
- 250 ml milk
- a pinch of salt

git diff

diff --git a/pancakes.md b/pancakes.md
index 871d830..fcc716f 100644
--- a/pancakes.md
+++ b/pancakes.md
@@ -2,4 +2,5 @@

 - 200 g flour
 - 2 eggs
-- 300 ml milk
+- 250 ml milk
+- a pinch of salt

git add pancakes.md

git diff

git diff --staged

diff --git a/pancakes.md b/pancakes.md
index 871d830..fcc716f 100644
--- a/pancakes.md
+++ b/pancakes.md
@@ -2,4 +2,5 @@

 - 200 g flour
 - 2 eggs
-- 300 ml milk
+- 250 ml milk
+- a pinch of salt

git commit -m "Use less milk and add salt"

[main b7b26af] Use less milk and add salt
 1 file changed, 2 insertions(+), 1 deletion(-)

git show

commit b7b26af362cd6db7ab58150f347b1c07ccfa83e5
Author: Alex Smith <alex@example.com>
Date:   Mon Jan 5 09:14:00 2026 +0000

    Use less milk and add salt

diff --git a/pancakes.md b/pancakes.md
index 871d830..fcc716f 100644
--- a/pancakes.md
+++ b/pancakes.md
@@ -2,4 +2,5 @@

 - 200 g flour
 - 2 eggs
-- 300 ml milk
+- 250 ml milk
+- a pinch of salt

The output of git diff is called a diff, and every diff has the same parts:

• diff --git a/pancakes.md b/pancakes.md names the file: a/ is the old version and b/ the new one. The index, --- and +++ lines that follow say the same in more detail, and you can skip them.
• @@ -2,4 +2,5 @@ starts a hunk, one block of changes. -2,4 means the block covers four lines of the old version, starting at line 2. +2,5 means it covers five lines of the new version, also starting at line 2: the new version is one line longer.
• Below it, each line starts with a marker. A line starting with - was removed, a line starting with + was added, and a line starting with a space is unchanged context, shown to help you find the place. Here, - 300 ml milk was replaced by - 250 ml milk, and - a pinch of salt was added. The first character of each line is the diff’s marker; the - after it belongs to the recipe’s list.

After git add pancakes.md, the second git diff prints nothing, because the working tree and the staging area now match. The change has not vanished: git diff --staged shows exactly the same diff, because the change now sits between the staging area and the last commit. Once you commit, git show displays it once more, with the commit’s hash, author, date and message above it.

git diff can also compare two commits: git diff <older> <newer>, with hashes from git log --oneline. The diff then shows how the newer commit differs from the older one: lines marked - are only in the older commit, and lines marked + only in the newer one. Exercise 2 practises this.

Mistakes are easiest to undo before they reach a commit. Two forms of git restore cover the two cases:

• git restore <file> throws away your edits to a file. It replaces the file in the working tree with the version in the staging area, which is the version from the last commit unless you have staged something since.
• git restore --staged <file> unstages a file. It takes the change out of the staging area, so that it will not go into the next commit, but leaves your edit in the working tree.

You do not need to memorise either: git status suggests both in its hints, as the session shows. First, the README’s description has been deleted by accident. Then a change to the pancake recipe, three eggs instead of two, is staged before it is ready.

# Family recipes

Oops: the description is gone.

git status

On branch main
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   README.md

no changes added to commit (use "git add" and/or "git commit -a")

git restore README.md

git status

On branch main
nothing to commit, working tree clean

cat README.md

# Family recipes

Recipes we cook again and again, with notes on what worked.

# Pancakes

- 200 g flour
- 3 eggs
- 300 ml milk

git add pancakes.md

git status

On branch main
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
	modified:   pancakes.md

git restore --staged pancakes.md

git status

On branch main
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   pancakes.md

no changes added to commit (use "git add" and/or "git commit -a")

After git restore README.md, git status reports a clean working tree, and cat shows the description again. After git restore --staged pancakes.md, the change is back under “Changes not staged for commit”: the three eggs are still in the file, but they are no longer staged. If you are following along, run git restore pancakes.md now to throw that edit away as well, so that your working tree is clean for the next section.

Older guides and many answers online use git checkout -- <file> to throw away edits and git reset HEAD <file> to unstage. Both still work, but git restore, added in Git 2.23, says what it does, and it is what git status suggests.

Sometimes you notice a mistake just after committing: a typo in the message, or a file you forgot to stage. As long as you have not shared the commit, git commit --amend fixes it by replacing the last commit with a new one:

• git commit --amend -m "new message" gives the commit a new message.
• git commit --amend --no-edit keeps the message, and adds whatever you have staged since.

With neither option, Git opens your editor with the old message, ready to change. In the session, you commit a soda bread recipe with a typo in the message, correct the message, and then notice that the recipe has no raising agent.

# Soda bread

- 450 g flour
- 400 ml buttermilk

git add bread.md

git commit -m "Add a sdoa bread recipe"

[main 087bb2c] Add a sdoa bread recipe
 1 file changed, 4 insertions(+)
 create mode 100644 bread.md

git commit --amend -m "Add a soda bread recipe"

[main 3fc0d24] Add a soda bread recipe
 Date: Mon Jan 5 09:11:00 2026 +0000
 1 file changed, 4 insertions(+)
 create mode 100644 bread.md

# Soda bread

- 450 g flour
- 400 ml buttermilk
- 1 teaspoon bicarbonate of soda

git add bread.md

git commit --amend --no-edit

[main 31783ba] Add a soda bread recipe
 Date: Mon Jan 5 09:11:00 2026 +0000
 1 file changed, 5 insertions(+)
 create mode 100644 bread.md

git log --oneline -n 2

31783ba Add a soda bread recipe
1ad5842 Say what the notes are for

git show --stat

commit 31783bacd01cd94e817a9f878b5a49d36be8dbf3
Author: Alex Smith <alex@example.com>
Date:   Mon Jan 5 09:11:00 2026 +0000

    Add a soda bread recipe

 bread.md | 5 +++++
 1 file changed, 5 insertions(+)

Look at the hashes. The first commit was 087bb2c; after the first amend the newest commit is 3fc0d24, and after the second it is 31783ba. Amending does not edit a commit in place, because a commit never changes once it is made. Git makes a new commit, with the same parent as the old one, and moves the branch to it. The old commit is no longer part of the branch, which is why git log --oneline -n 2 shows 31783ba directly above 1ad5842. git show --stat confirms that the new commit holds all five lines of bread.md.

The Date: line in each amend’s output is the time of the original commit: an amended commit keeps its original author and date.

--amend reaches only the newest commit, and it rewrites history. For a commit that is older, or that others already have, use git revert <commit>. It removes nothing: it makes a new commit that undoes the old commit’s changes. Lines that the old commit added are removed, and lines it removed are put back.

You name the commit to undo by its hash, or as HEAD, Git’s name for the commit you are on, normally the newest on your branch. Revert needs a clean working tree, so commit or restore your edits first. In the session, a mistake slips in: the pancake recipe asks for 2000 g of flour instead of 200 g.

# Pancakes

- 2000 g flour
- 2 eggs
- 300 ml milk

git add pancakes.md

git commit -m "Use more flour"

[main 654de4f] Use more flour
 1 file changed, 1 insertion(+), 1 deletion(-)

git revert HEAD

[main 4407f3a] Revert "Use more flour"
 Date: Mon Jan 5 09:12:00 2026 +0000
 1 file changed, 1 insertion(+), 1 deletion(-)

git log --oneline -n 3

4407f3a Revert "Use more flour"
654de4f Use more flour
1ad5842 Say what the notes are for

cat pancakes.md

# Pancakes

- 200 g flour
- 2 eggs
- 300 ml milk

git revert HEAD made a new commit, 4407f3a, with the message Revert "Use more flour". On your computer, Git first opens your editor with this ready-made message, followed by a line saying which commit it reverts. Save and close the editor to accept it; the sessions here accept it automatically. The Date: line is simply the time of the new commit.

The log now shows both commits: the mistake, 654de4f, and the commit that undoes it, 4407f3a. That may look untidy, but it is honest, and it is safe on a branch that others share: nobody’s history is rewritten, they simply receive one more commit. cat confirms that the recipe asks for 200 g of flour again.

You can revert any commit, not only the newest, by giving its hash. If later commits changed the same lines, Git may stop with a conflict for you to resolve, which Module 5 explains.

Sometimes you want to see how the project looked earlier: to find out when something still worked, or to copy an old paragraph back. Git offers two safe ways to look.

To see one file, use git show <commit>:<file>. It prints the file as it was in that commit, and changes nothing. You can name a commit by its hash, or by counting back from HEAD: HEAD~1 is the commit before the one you are on, and HEAD~2 the one before that.

To see the whole project, use git switch --detach <commit>. It puts every file in the working tree back to that commit, so that you can look around, open files or run the project, and it leaves your branch untouched. HEAD, Git’s marker for where you are, then points straight at a commit instead of at a branch. Git calls this a detached HEAD.

You have made more commits by now, so in your repository HEAD~2 is a different commit. To follow along, use the hash of your first commit, Add a README, from git log --oneline.

git show HEAD~2:README.md

# Family recipes

Recipes we cook again and again.

git switch --detach HEAD~2

HEAD is now at 907a979 Add a README

git status

HEAD detached at 907a979
nothing to commit, working tree clean

cat README.md

# Family recipes

Recipes we cook again and again.

* 1ad5842 (main) Say what the notes are for
* 8bf3c2d Add a pancake recipe
* 907a979 (HEAD) Add a README

git switch main

Previous HEAD position was 907a979 Add a README
Switched to branch 'main'

git status

On branch main
nothing to commit, working tree clean

git show HEAD~2:README.md printed the README’s first wording, and git switch --detach HEAD~2 reported the move: HEAD is now at 907a979 Add a README. git status no longer says On branch main but HEAD detached at 907a979, and cat README.md shows the old wording in the working tree itself.

The graph shows where everything is. main still points at the newest commit, 1ad5842, while HEAD sits alone on 907a979. Nothing has been lost or changed: the newer commits are all still there, and git switch main takes you back. Git tells you where you came from (Previous HEAD position was 907a979), and git status says On branch main again.

Older guides use git checkout <commit> for the same thing. It detaches HEAD as well, and prints a longer explanation when it does.

git log --oneline

1ad5842 Say what the notes are for
8bf3c2d Add a pancake recipe
907a979 Add a README

git diff HEAD~2 HEAD

diff --git a/README.md b/README.md
index 2ecc1f2..130cb17 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,3 @@
 # Family recipes

-Recipes we cook again and again.
+Recipes we cook again and again, with notes on what worked.
diff --git a/pancakes.md b/pancakes.md
new file mode 100644
index 0000000..871d830
--- /dev/null
+++ b/pancakes.md
@@ -0,0 +1,5 @@
+# Pancakes
+
+- 200 g flour
+- 2 eggs
+- 300 ml milk

passwords.txt

git rm --cached passwords.txt

rm 'passwords.txt'

git status

On branch main
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
	deleted:    passwords.txt

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	.gitignore

git add .gitignore

git commit -m "Stop tracking the passwords file"

[main 908ddf5] Stop tracking the passwords file
 2 files changed, 1 insertion(+), 1 deletion(-)
 create mode 100644 .gitignore
 delete mode 100644 passwords.txt

git status

On branch main
nothing to commit, working tree clean

ls

README.md  pancakes.md  passwords.txt

git add butter.md
git commit --amend --no-edit

• Scott Chacon and Ben Straub, Pro Git, sections 2.3: Viewing the Commit History and 2.4: Undoing Things.
• The reference pages for git log, git diff, git restore and git revert.