Git Log Mastery — History, Diff, Blame

# Visual graph (bookmark this)
git log --oneline --graph --all --decorate

# Filter by author
git log --author="Akshay"
git log --author="akshay|john"   # multiple authors (regex)

# Filter by date
git log --since="2024-01-01"
git log --until="yesterday"
git log --since="2 weeks ago" --until="1 week ago"

# Filter by commit message
git log --grep="payment"         # case-sensitive
git log --grep="payment" -i      # case-insensitive
git log --grep="fix" --grep="auth" --all-match  # both terms

# Find commits that added/removed a specific string (pickaxe)
git log -S "validateEmail"       # string added or removed
git log -G "validate.*Email"     # regex in diff content

# Filter by file
git log -- src/auth.js           # commits touching this file
git log -- "*.test.js"           # all test files

# Combine filters
git log --author="Akshay" --since="1 month ago" -- src/payment/

# Built-in formats
git log --oneline           # short hash + subject
git log --short             # slightly more detail
git log --full              # full hash
git log --fuller            # author + committer info

# Custom format placeholders
# %H = full hash, %h = short hash
# %s = subject, %b = body
# %an = author name, %ae = author email
# %ar = relative date, %ad = absolute date
# %Cred / %Cgreen / %Creset = colours

git log --pretty=format:"%h | %an | %ar | %s"
# a3f8c12 | Akshay | 2 days ago | Add payment gateway

git log --pretty=format:"%Cgreen%h%Creset %s (%an, %ar)"

# Use in shell scripts / CI
git log --format="%H" -20        # last 20 commit hashes
git log --format="%s" HEAD~5..HEAD  # last 5 commit subjects

# Working directory vs staging area
git diff                     # what's not yet staged

# Staging area vs last commit
git diff --staged            # what will go into the next commit

# Two commits
git diff HEAD~3 HEAD         # last 3 commits' net changes
git diff a3f8c12 9d2e441     # specific commits
git diff a3f8c12..9d2e441    # same (range syntax)

# Two branches
git diff main feature/cart
git diff main..feature/cart

# Only show file names (not the diffs)
git diff --name-only main feature/cart
git diff --stat HEAD~5 HEAD  # files + line counts

# Diff a specific file only
git diff HEAD~1 -- src/auth.js

# Ignore whitespace changes
git diff -w
git diff --ignore-all-space

# Who wrote each line and when?
git blame src/auth.js
# a3f8c12 (Akshay 2024-01-10) function validateEmail(email) {
# 9d2e441 (John   2024-01-08)   return /S+@S+.S+/.test(email)

# Show only certain lines
git blame -L 10,25 src/auth.js

# Show the last commit that touched a range of lines
git log -L 10,25:src/auth.js

# ── git bisect: binary search for a bug ──────────────────
git bisect start

# Mark current commit as bad (has the bug)
git bisect bad

# Mark a known good commit (before the bug existed)
git bisect good v2.0.0

# Git checks out the midpoint — you test and tell it:
git bisect good   # if this commit is fine
git bisect bad    # if this commit has the bug

# Git narrows down in ~logâ‚‚(n) steps
# "bisect found: 7b2e441 is the first bad commit"

git bisect reset  # return to original HEAD when done