git log & History Navigation

Quick Summary

git log is your time machine — it shows the complete history of commits in your repository. From simple chronological lists to complex filtered searches, mastering the log is essential for understanding what happened, when, and why.

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Basic Log

git log

commit a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0 (HEAD -> main, origin/main)
Author: donnyaw <donnyaw@gmail.com>
Date:   Mon Feb 17 08:00:00 2026 +0800

    feat: add user authentication module

commit b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1
Author: donnyaw <donnyaw@gmail.com>
Date:   Sun Feb 16 15:30:00 2026 +0800

    fix: correct validation regex for email input

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Useful Log Formats

One line per commit

git log --oneline

a1b2c3d feat: add user authentication module
b2c3d4e fix: correct validation regex for email input
c3d4e5f docs: update API documentation
d4e5f6a refactor: extract database helpers

Graph view

git log --oneline --graph --all

*   a1b2c3d (HEAD -> main) Merge branch 'feature/auth'
|\
| * f6a7b8c feat: add login endpoint
| * e5f6a7b feat: add user model
|/
* d4e5f6a fix: update dependencies
* c3d4e5f Initial commit

Detailed with stats

git log --stat

commit a1b2c3d
Author: donnyaw <donnyaw@gmail.com>
Date:   Mon Feb 17 08:00:00 2026 +0800

    feat: add user authentication module

 src/auth.js    | 45 +++++++++++++++++++++
 src/models.js  | 12 ++++++
 test/auth.test.js | 30 ++++++++++++++
 3 files changed, 87 insertions(+)

Custom format

git log --pretty=format:"%h %ad | %s%d [%an]" --date=short

a1b2c3d 2026-02-17 | feat: add auth module (HEAD -> main) [donnyaw]
b2c3d4e 2026-02-16 | fix: validation regex [donnyaw]
c3d4e5f 2026-02-15 | docs: update API docs [donnyaw]

Format Placeholders

Placeholder	Meaning
%H / %h	Full / short commit hash
%an	Author name
%ae	Author email
%ad	Author date
%s	Subject (first line of message)
%d	Ref names (branches, tags)
%b	Body of commit message

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Filtering History

By Author

git log --author="donnyaw"
git log --author="donnyaw\|alice"    # Multiple authors

By Date

git log --since="2026-01-01"
git log --after="2 weeks ago"
git log --until="2026-02-01"
git log --since="2026-01-01" --until="2026-02-01"

By Message Content

git log --grep="fix"                  # Commits mentioning "fix"
git log --grep="auth" --grep="login" --all-match  # Both terms

By File

git log -- src/auth.js                # Commits that touched this file
git log --follow -- old-name.js       # Follow renames
git log -p -- src/auth.js             # Show patches for this file

By Number

git log -5                            # Last 5 commits
git log -1                            # Last commit only

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Advanced History Commands

git show — Inspect a Single Commit

git show a1b2c3d

Shows the commit metadata + full diff of changes.

git blame — Who Changed Each Line?

git blame src/auth.js

a1b2c3d4 (donnyaw 2026-02-17 08:00:00 +0800  1) const jwt = require('jsonwebtoken');
b2c3d4e5 (donnyaw 2026-02-16 15:30:00 +0800  2) const bcrypt = require('bcrypt');
c3d4e5f6 (alice   2026-02-10 10:00:00 +0800  3)
a1b2c3d4 (donnyaw 2026-02-17 08:00:00 +0800  4) function login(user, password) {

git shortlog — Summary by Author

git shortlog -sn

    42  donnyaw
    15  alice
     3  bot

git reflog — Recovery Safety Net

git reflog

a1b2c3d HEAD@{0}: commit: feat: add auth module
b2c3d4e HEAD@{1}: checkout: moving from feature to main
f6a7b8c HEAD@{2}: commit: feat: add login endpoint

Reflog is your safety net

Even if you accidentally delete a branch or reset to the wrong commit, reflog shows every position HEAD has been in. You can recover almost anything with it.

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Quick Reference

What You Want	Command
Simple history	git log --oneline
Visual branch graph	git log --oneline --graph --all
Changes in each commit	git log --stat
Full diff for each commit	git log -p
Filter by author	git log --author="name"
Filter by date	git log --since="2 weeks ago"
Filter by message	git log --grep="keyword"
History of one file	git log -- <file>
Who wrote each line	git blame <file>
Inspect one commit	git show <hash>
Recovery (HEAD movements)	git reflog

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Troubleshooting

Problem	Cause	Fix
Log shows too many commits	No filter applied	Use -n 10 or --since
Can't find a commit	Wrong branch	Add --all to search all branches
Author search returns nothing	Name mismatch	Use partial match: --author="don"
git blame shows merge commits	Merge introduced the lines	Use git blame -w -M to ignore whitespace/moves

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Best Practices

• Use --oneline --graph for quick visual overview
• Set up a Git alias: git config --global alias.lg "log --oneline --graph --all --decorate"
• Use git blame to understand context before modifying unfamiliar code
• Know git reflog exists — it can save you from disasters

What's Next

1. stash & clean — Save work temporarily or clean up untracked files
2. Branching Fundamentals — Work in parallel with branches