History, Diffs and Logs

Git history is a searchable record. Knowing how to read it turns debugging from guesswork into investigation.

Reading Logs

The default log is verbose. Use flags to make it readable.

git log --oneline
git log --oneline --graph --all
git log --stat
git log -p -- index.html

Comparing

git diff shows unstaged changes. git diff --staged shows staged changes. Comparing two commits shows what changed between them.

git diff
git diff --staged
git diff HEAD~1 HEAD
git diff main feature-login

Blame and Search

git blame shows the last commit for each line. git log -S finds the commit that added or removed a string.

git blame index.html
git log -S "validateEmail" --oneline

Practice

1. Show the last five commits in one line each.
2. Compare the working directory with the last commit.
3. Find the commit that introduced a specific function name.

Hands-on exercise

In a repository with at least three commits:
1. Print a one-line graph of all branches.
2. Show the full diff of the most recent commit.
3. Use git blame on one file and identify the commit for its first line.

Recap

Logs show what happened, diffs show what changed and blame ties each line to a commit.