Git Blame & Log: Who Changed What?

Git Blame

git blame shows who last modified each line of a file, and when:

git blame index.html

Output:

a1b2c3d4 (Alice  2024-01-15) <html>
a1b2c3d4 (Alice  2024-01-15) <head>
e5f6g7h8 (Bob    2024-02-20)   <title>My App</title>
a1b2c3d4 (Alice  2024-01-15) </head>
i9j0k1l2 (Charlie 2024-03-10) <body class="dark">

When to Use Blame

Understanding code: Who wrote this? What was the context?
Finding bugs: Who introduced this change?
Code review: When was this last modified?

Blame Options

git blame file.txt               # Full blame
git blame -L 10,20 file.txt      # Only lines 10-20
git blame -w file.txt             # Ignore whitespace changes
git blame --since="2024-01-01"    # Changes after date

Git Log

git log shows the commit history. It's your project's diary.

# Basic log
git log
Compact one-line format
git log --oneline
With graph visualization
git log --oneline --graph --all
Filter by author
git log --author="Alice"
Filter by date
git log --since="2024-01-01" --until="2024-06-01"
Filter by file
git log -- path/to/file.js
Search commit messages
git log --grep="fix bug"

Git Show

View the details of a specific commit:

git show abc1234

This shows:

The commit message
The author and date
The exact changes (diff)

Practical Investigation

Here's how experienced developers track down issues:

# 1. Find when a file was last changed
git log --oneline -- src/login.js
2. See who modified line 42
git blame -L 42,42 src/login.js
3. View that commit's full details
git show abc1234
4. See what else changed in that commit
git show --stat abc1234

Summary

Command	Purpose
<code>git blame file</code>	Show who changed each line
<code>git blame -L 10,20 file</code>	Blame specific lines
<code>git log --oneline</code>	Compact commit history
<code>git log --graph --all</code>	Visual branch history
<code>git show HASH</code>	Details of one commit
<code>git log --author="name"</code>	Filter by author