git blame for line-by-line history - Mini Project: Build & Apply

git blame for line-by-line history

📖 Scenario: You are working on a small project with a file called app.py. You want to find out who last changed each line in this file to understand the history better.

🎯 Goal: Learn how to use git blame to see line-by-line history of changes in a file.

📋 What You'll Learn

Have a git repository initialized

Have a file named app.py with at least 3 lines of code

Use git blame to see who last changed each line

💡 Why This Matters

🌍 Real World

Developers often need to find out who last changed a specific line of code to understand why a change was made or to ask questions.

💼 Career

Knowing how to use <code>git blame</code> is essential for debugging, code reviews, and collaborating in software development teams.

1

Create a file app.py with 3 lines of code

Create a file called app.py with these exact lines:
print('Hello World')
print('Welcome to git blame')
print('This is line 3')

Git

# Create the file app.py with the 3 lines exactly as instructed
# Your code here

Hint

Use a text editor or command line to create app.py with the exact lines.

2

Add and commit the file to git

Add the file app.py to git staging area using git add app.py and commit it with the message Initial commit with app.py using git commit -m "Initial commit with app.py"

Git

print('Hello World')
print('Welcome to git blame')
print('This is line 3')
# Add app.py to git and commit with message "Initial commit with app.py"
# Your code here

Hint

Use git add to stage and git commit -m to commit with the exact message.

3

Modify the second line in app.py

Change the second line in app.py to print('Welcome to the git blame tutorial') exactly, then add and commit the change with message Update welcome message

Git

print('Hello World')
print('Welcome to git blame')
print('This is line 3')

# Modify the second line as instructed
# Add and commit the change with message "Update welcome message"
# Your code here

Hint

Edit the file to change the second line exactly, then stage and commit with the exact message.

4

Use git blame to see line-by-line history of app.py

Run the command git blame app.py to display who last changed each line in app.py.

Git

print('Hello World')
print('Welcome to the git blame tutorial')
print('This is line 3')

# Run git blame on app.py below
# Your code here

Hint

Simply run git blame app.py to see the line-by-line history.

Practice

1. What does the git blame command primarily show?

easy

A. Who last changed each line in a file

B. The current status of the repository

C. The list of branches in the repository

D. The commit history summary

Solution

1. Step 1: Understand the purpose of git blame

   git blame is used to show the author information for each line in a file, indicating who last modified that line.

2. Step 2: Compare with other git commands

   Other commands like git status, git branch, and git log serve different purposes, not line-by-line author tracking.

3. Final Answer:

   Who last changed each line in a file -> Option A

4. Quick Check:

   git blame = line author info [OK]

Hint: Remember: blame = who changed each line last [OK]

Common Mistakes:

• Confusing git blame with git log
• Thinking git blame shows branch info
• Assuming git blame shows file status

2. Which of the following is the correct syntax to show blame for a file named app.js?

easy

A. git blame --file app.js

B. git blame app.js

C. git blame --show app.js

D. git blame -f app.js

Solution

1. Step 1: Recall basic git blame syntax

   The basic syntax to run blame on a file is simply git blame <filename>. No extra flags are needed for a simple blame.

2. Step 2: Check the options given

   Options like -f, --show, or --file are not valid or required for basic blame usage.

3. Final Answer:

   git blame app.js -> Option B

4. Quick Check:

   Basic blame = git blame filename [OK]

Hint: Use just 'git blame filename' for simple blame [OK]

Common Mistakes:

• Adding unnecessary flags
• Using incorrect or unsupported options
• Confusing blame syntax with other git commands

3. Given the command git blame -L 10,15 README.md, what will it show?

medium

A. Blame info for lines 1 to 15 of README.md

B. Blame info for the whole README.md file

C. Blame info for lines 10 to 15 of README.md

D. An error because -L requires a commit hash

Solution

1. Step 1: Understand the -L option in git blame

   The -L option limits the blame output to a specific line range. Here, -L 10,15 means lines 10 through 15.

2. Step 2: Apply to the file README.md

   The command will show blame info only for lines 10 to 15 of the file README.md, not the entire file or any other range.

3. Final Answer:

   Blame info for lines 10 to 15 of README.md -> Option C

4. Quick Check:

   -L limits lines = lines 10-15 [OK]

Hint: -L start,end shows blame only for those lines [OK]

Common Mistakes:

• Assuming -L shows whole file blame
• Thinking -L needs a commit hash
• Confusing line numbers with byte offsets

4. You run git blame --since=2.weeks README.md but get an error. What is the likely cause?

medium

A. You need to specify a commit hash with --since

B. README.md file does not exist

C. Incorrect date format for --since option

D. git blame does not support --since option

Solution

1. Step 1: Check if git blame supports --since

   The git blame command does not have a --since option. This option is valid for git log but not for blame.

2. Step 2: Understand the error cause

   Using an unsupported option causes git blame to error out. The file existence or commit hash is unrelated here.

3. Final Answer:

   git blame does not support --since option -> Option D

4. Quick Check:

   git blame lacks --since option [OK]

Hint: git blame has no --since; use git log for date filters [OK]

Common Mistakes:

• Assuming git blame supports --since
• Blaming file existence without checking
• Thinking commit hash is mandatory with --since

5. You want to find who last changed line 42 in server.py but only for commits on the feature branch. Which command correctly achieves this?

hard

A. git blame feature -- server.py -L 42,42

B. git blame -L 42,42 server.py feature

C. git blame -L 42,42 -- server.py feature

D. git blame -L 42,42 --first-parent feature -- server.py

Solution

1. Step 1: Understand branch limitation in git blame

   To blame a file as it appears on a specific branch, specify the branch name before the -- separator, then the file name.

2. Step 2: Apply line range and branch correctly

   The correct syntax is git blame <branch> -- <file> -L <start,end>. So git blame feature -- server.py -L 42,42 limits blame to line 42 on the feature branch.

3. Final Answer:

   git blame feature -- server.py -L 42,42 -> Option A

4. Quick Check:

   Branch before --, file after, -L for lines [OK]

Hint: Put branch before --, file after, use -L for lines [OK]

Common Mistakes:

• Placing branch after file name
• Misordering -L option
• Using unsupported options like --first-parent with blame