Chapter 3: Branch, Merge, Rebase, Stash and Pull Requests

3.12 log --graph, diff and show

By Ravindra Bagale · Last updated: 25 October 2026

Why: the problem

In a production incident, the first question is: what changed? Git answers it with three tools. git log shows the history: who committed, when and why, and with --graph you see branches and merges. git diff shows what changed between any two points: working tree, staging area, commits or branches. git show shows one commit fully: message and diff. Senior engineers at Zomato or Razorpay use these every day to review MRs, find the commit that broke something, and write release notes. In this lesson you will use the most useful options on hello-shop: graph views, filters by author, date, file and text, diff of staged changes and between branches, word diff, and show for one file at an old version.

What we will build

You will read hello-shop history with log --graph and filters, compare working tree, staging and branches with diff, and inspect commits and old file versions with show.

What: every term in plain English

• git log --oneline --graph --decorate --all — Picture of all branches.
• git log -p FILE — History with diffs for one file.
• git log -S TEXT — Commits that added or removed TEXT.
• git log --since / --author — Filter by date or person.
• git diff — Working tree vs staging area.
• git diff --staged — Staging area vs last commit.
• git diff A..B — Between two commits or branches.
• git show HASH:FILE — A file as it was at that commit.

How: step by step

1. Graph of all

   cd ~/devops-lab/hello-shop && git log --oneline --graph --decorate --all -8
   

   What it does: All branches.

   Output

   *   4d4d4d4 (HEAD -> main) Merge branch 'feature/badge-colour'
   |\
   | * 2b2b2b2 Gold badge
   

2. Short alias

   git config --global alias.lg "log --oneline --graph --decorate --all" && git lg -3
   

   What it does: Save typing.

   Output

   * 4d4d4d4 (HEAD -> main) ...
   

3. By file

   git log --oneline -- badge.py
   

   What it does: Only badge commits.

   Output

   4d4d4d4 Merge ...
   3c3c3c3 Set campaign colour to blue
   2b2b2b2 Gold badge
   

4. By text

   git log -S "BADGE_COLOR" --oneline
   

   What it does: Where that word came or went.

   Output

   1e1e1e1 Add badge
   

5. Unstaged diff

   echo "x=1" >> badge.py && git diff
   

   What it does: Edits not yet added.

   Output

   +x=1
   

6. Staged diff

   git add badge.py && git diff --staged --stat
   

   What it does: Ready to commit.

   Output

   badge.py | 1 +
   

7. Undo

   git restore --staged badge.py && git restore badge.py
   

   What it does: Clean.

   Output

   (no output)
   

Example 1: Find what changed between two releases

Stack. Git

Goal. Find what changed between two releases.

release-diff.sh

git tag -l
git log --oneline v1.0.0..main
git diff --stat v1.0.0..main
git log --format="- %s (%an)" --no-merges v1.0.0..main

What each line does

• A..B — Commits in B not in A.
• --stat — Files and line counts.
• --format — Make release notes.
• --no-merges — Skip merge commits.

Green output

v1.0.0
4d4d4d4 Merge branch 'feature/badge-colour'
3c3c3c3 Set campaign colour to blue
2b2b2b2 Gold badge
 badge.py | 1 +
 1 file changed, 1 insertion(+)
- Set campaign colour to blue (Ravi Learner)
- Gold badge (Ravi Learner)

Expected result. Release notes and a change list in seconds.

Example 2: Investigate a production bug: who changed this line?

Stack. Git

Goal. Investigate a production bug: who changed this line?

investigate.sh

git blame -L 1,1 badge.py
git show --stat 2b2b2b2
git log -p -1 2b2b2b2 -- badge.py

What each line does

• blame -L — Who last changed line 1.
• show --stat — Commit info and files.
• log -p — The exact diff.

Green output

2b2b2b2 (Ravi Learner 2026-10-20 11:02:13 +0530 1) BADGE_COLOR = "gold"
commit 2b2b2b2...
Author: Ravi Learner <ravi@example.com>
    Gold badge
 badge.py | 2 +-
-BADGE_COLOR = "green"
+BADGE_COLOR = "gold"

Expected result. You found the commit, the author and the reason in three commands.

Example 3: See an old file version without switching

Stack. Git

Goal. See an old file version without switching.

old.sh

git show 1e1e1e1:badge.py
git show main~3:badge.py > /tmp/badge-old.py
diff -u /tmp/badge-old.py badge.py | tail -2
git restore --source=1e1e1e1 --worktree badge.py && cat badge.py && git restore badge.py

What each line does

• HASH:FILE — The file at that commit.
• > /tmp/... — Save it.
• restore --source — Put an old version in your working tree.

Green output

BADGE_COLOR = "green"
-BADGE_COLOR = "green"
+BADGE_COLOR = "gold"
BADGE_COLOR = "green"

Expected result. Read or restore any old version safely.

Example 4: Compare branches before opening an MR

Stack. Git

Goal. Compare branches before opening an MR.

mr-check.sh

git fetch -q
git log --oneline main..feature/offers
git diff --stat main...feature/offers
git diff --word-diff main...feature/offers -- offers.txt

What each line does

• main..feature — Commits only on the feature.
• three dots — Diff from the merge base, what the MR will show.
• --word-diff — Shows changed words, easy for config.

Green output

6c6c6c6 Cap offer
0d0d0d0 Add offers
 offers.txt | 3 +++
{+offer=10+}
{+offer_max=40+}

Expected result. You see exactly what reviewers will see before you push.

Example 5: Summaries by author and message search

Stack. Git

Goal. Summaries by author and message search.

summary.sh

git shortlog -sn --no-merges
git log --grep "SHOP-2" --oneline
git log --since "2 weeks ago" --author Ravi --oneline | wc -l

What each line does

• shortlog -sn — Commit count per author.
• --grep — Search messages.
• --since --author — Recent work by one person.

Green output

    14  Ravi Learner
     3  Asha Patil
5f5f5f5 Add /search route (!7)
5e5e5e5 Add steps file (SHOP-240)
12

Expected result. Good for standups and sprint reviews.

Example 6: Diff only names and status

Stack. Git

Goal. Diff only names and status.

names.sh

git diff --name-status v1.0.0..main
git diff --name-only HEAD~2 HEAD

What each line does

• --name-status — A added, M modified, D deleted.
• --name-only — Only paths, good for scripts.

Green output

M   badge.py
A   offers.txt
badge.py

Expected result. Handy in CI to run tests only for changed folders.

Example 7: Follow a renamed file

Stack. Git

Goal. Follow a renamed file.

follow.sh

git mv badge.py ui_badge.py && git commit -qm "Rename badge"
git log --oneline -- ui_badge.py | wc -l
git log --oneline --follow -- ui_badge.py | wc -l
git mv ui_badge.py badge.py && git commit -qm "Rename back"

What each line does

• Without --follow — Only commits after the rename.
• --follow — Full history.

Green output

1
5

Expected result. Always use --follow when a file was renamed.

Verify: did it work?

1. Alias works

   git lg -1
   

   What it does: One line with labels.

   Output

   * 4d4d4d4 (HEAD -> main) ...
   

2. Clean tree

   git status -s
   

   What it does: Nothing.

   Output

   (no output)
   

3. Last commit

   git show --stat --oneline -1
   

   What it does: Commit info.

   Output

   4d4d4d4 Merge branch ...
   

When it is red 1

fatal: ambiguous argument 'v1.0.0..main': unknown revision

Cause. Tag does not exist locally.

Fix, step by step

1. git fetch --tags
2. git tag -l

When it is red 2

git log shows nothing for a file

Cause. The path is wrong or the file was renamed.

Fix, step by step

1. Use git log --follow -- FILE.

When it is red 3

fatal: path 'badge.py' exists on disk, but not in '1e1e1e0'

Cause. The file did not exist in that commit.

Fix, step by step

1. Pick a later commit: git log -- badge.py

When it is red 4

Output stuck in a pager (END)

Cause. Git uses less for long output.

Fix, step by step

1. Press q, or use git --no-pager log.

Cleanup

1. Nothing to clean

   git status -s
   

   What it does: Clean.

   Output

   (no output)
   

Practice tasks

Homework: try at home

Recap

• log shows history; filter by file, text, date, author.
• diff compares any two states.
• show prints one commit or old file.
• blame finds the line owner.
• Three dots diff equals the MR view.

FAQ

Two dots vs three dots in diff?

Two: tip vs tip. Three: from the merge base.

What is --follow?

Track a file across renames.

How do I see only file names?

git diff --name-only

Can I search commit messages?

git log --grep WORD

What is git shortlog?

Groups commits by author, good for summaries.

How do I see a diff of one function?

git log -L :NAME:FILE shows the history of a function.

Interview questions

1. How do you find which commit introduced a bug?

   git log -S, git blame, or git bisect.

2. Difference between git diff and git diff --staged?

   Unstaged changes vs staged changes.

3. How do you view a file at an older commit?

   git show HASH:path.

4. How do you generate release notes?

   git log --no-merges --format from the last tag.

5. What does --graph show?

   The branch and merge shape of history.

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