git blame for line-by-line history - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the git blame command do?

It shows who last changed each line in a file, along with the commit details and timestamp.

beginner

How can you use git blame to see changes for a specific file?

Run git blame filename to see line-by-line history for that file.

beginner

What information does each line in git blame output include?

It includes the commit hash, author name, date, and the actual line content.

intermediate

How can git blame help when debugging?

It helps identify who introduced a change and when, making it easier to ask questions or fix bugs.

intermediate

What option can you add to git blame to ignore whitespace changes?

Use git blame -w filename to ignore whitespace-only changes in the history.

What does git blame primarily show?

A Who last modified each line of a file

B The current status of the repository

C The list of branches

D The commit log summary

git blame shows the last person who changed each line in a file.

Which command shows line-by-line history for a file named app.js?

A git blame app.js

B git log app.js

C git status app.js

D git diff app.js

git blame app.js shows who changed each line in app.js.

What extra info does git blame show besides the author?

A File size

B Branch name

C Commit hash and date

D Remote URL

It shows commit hash, author, date, and the line content.

How do you ignore whitespace changes in git blame?

A git blame --skip-whitespace

B git blame --ignore-space

C git blame --no-whitespace

D git blame -w filename

The -w option ignores whitespace-only changes.

Why is git blame useful in debugging?

A It resets the repository

B It shows who introduced each line, helping track bugs

C It merges conflicting changes

D It deletes buggy lines automatically

Knowing who changed a line helps understand and fix bugs faster.

Explain how git blame helps you understand the history of a file.

Think about how knowing who changed each line can help.

Describe the command and option to ignore whitespace changes when using git blame.

Look for a flag that starts with a dash and relates to whitespace.

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