git blame for line-by-line history - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Identify the commit hash from git blame output

You run git blame -L 10,10 README.md and see this output:

e3a1b2c4 (Alice 2024-05-01 10:15:30 +0000 10) Fix typo in introduction

What is the commit hash for the change on line 10?

A Alice

B e3a1b2c4

C 2024-05-01

D 10

💡 Hint

The commit hash is the first part before the author name.

The commit hash is the unique identifier for the commit and appears at the start of the git blame line.

🧠 Conceptual

intermediate

Purpose of git blame

What is the main purpose of the git blame command?

A To show who last modified each line of a file

B To undo the last commit

C To merge two branches

D To list all branches

💡 Hint

Think about tracking changes line by line.

git blame shows the author and commit info for each line in a file.

❓ Troubleshoot

advanced

Why does git blame show wrong author for a line?

You notice git blame shows an unexpected author for a line you recently changed. What could cause this?

A You forgot to stage the file before committing

B You ran <code>git blame</code> on a different branch

C The line was copied from another file without changes

D Your local git config has wrong user.email

💡 Hint

Think about how git tracks line history when lines are copied.

If a line is copied from another file or commit without changes, git blame attributes it to the original author.

🔀 Workflow

advanced

Using git blame to find when a bug was introduced

You want to find when a bug was introduced in a file. Which git command sequence helps you use git blame effectively?

A Run <code>git blame</code> on the buggy line, then use <code>git show</code> on the commit hash

B Run <code>git log</code> to list commits, then <code>git merge</code> to combine fixes

C Run <code>git diff</code> between branches, then <code>git blame</code> on the whole file

D Run <code>git reset</code> to undo changes, then <code>git blame</code> to check authors

💡 Hint

First find the commit that last changed the line, then inspect that commit.

Using git blame on the line shows the commit hash that last changed it. Then git show reveals details of that commit.

✅ Best Practice

expert

Optimizing git blame output for large files

For a large file, running git blame is slow. Which option improves performance without losing line history?

A Use <code>git blame --show-name</code> to display file names

B Use <code>git blame --incremental</code> to get detailed output efficiently

C Use <code>git blame --reverse</code> to blame lines backwards

D Use <code>git blame --ignore-rev</code> with a commit hash to skip known refactors

💡 Hint

Skipping commits that only refactor code can speed up blame.

Using --ignore-rev skips commits that do not affect logic, improving blame speed and clarity.