Reading Git History

Git is not only for saving changes.

It is also for understanding how the project reached its current state.

When a bug appears, history helps answer:

• When was this line added?
• Which commit introduced the behavior?
• Why was this file changed?
• Who should I ask for context?

git log

Show commit history:

git log

A more compact view:

git log --oneline

Example:

7a91c2d Fix token expiry bug
4b18f93 Add login validation
1e83a91 Add login endpoint

Each line is a commit.

The short code at the start is the commit hash.

git show

See what a commit changed:

git show 7a91c2d

This shows:

• commit message,
• author,
• date,
• changed files,
• line-level diff.

Use this when someone says, "This broke after that commit."

git diff between commits

Compare two commits:

git diff 1e83a91 7a91c2d

Compare your branch with main:

git diff main..feature-branch

This helps before opening a pull request.

git blame

See when each line was last changed:

git blame src/auth.js

Despite the name, blame should not be used to attack people.

Use it to find context.

The real question is usually:

What problem was this code solving when it was written?

Common workflow

If you find strange code:

git blame src/payment.js
git show <commit-hash>
git log --oneline -- src/payment.js

This lets you inspect the file's history before changing it.

Interview answer

I use git log to see commit history, git show to inspect a specific commit, git diff to compare changes, and git blame to find when a line was last changed. These commands help debug regressions and understand project decisions.