Git Cheat Sheet: Diffing and Commit References

Diffing and Commit References

diff answers “what changed?” In Git, first distinguish three states: the working tree, staging area, and most recent commit.

Working-tree and staging-area differences

git diff

git diff

Purpose: view working-tree modifications not yet staged.

Appropriate when:

• inspecting what you changed before git add;
• quickly confirming a local difference after code changes.

git diff --staged

git diff --staged

Purpose: view staged changes that will enter the next commit.

Equivalent common form:

git diff --cached

Appropriate when:

• reviewing commit content before git commit;
• confirming selections after git add -p.

git diff HEAD

git diff HEAD

Purpose: view tracked-path differences from the most recent commit to the current working tree, including staged and unstaged content. Ordinary untracked files do not appear, so still inspect git status --short.

Appropriate when:

• you want a single overview of “everything in the current directory versus the last commit”;
• doing a total review before a commit.

Differences between commits

git show <commit>

git show HEAD~1

Purpose: view a commit’s metadata and the difference it introduced relative to its parent.

Appropriate when:

• reviewing what a particular commit actually changed;
• understanding one commit’s concrete content before code review.

git diff <commit> <commit>

git diff main feature/demo

Purpose: compare content differences between two commits.

Examples:

git diff main feature-branch
git diff HEAD~3 HEAD

Order affects display direction. Usually read it as “change from the first commit to the second.”

git diff <commit> -- <file>

git diff HEAD~1 -- README.md

Purpose: view how one file changed from a specified commit to current state.

Appropriate when:

• you care about one file, not the entire repository;
• confirming how one configuration or document differs from an older version.

git diff <commit> --stat

git diff HEAD~1 --stat
git show HEAD~1 --stat

Purpose: view a difference summary instead of a complete patch.

Appropriate when:

• judging change scale quickly;
• summarizing touched files for handoff notes.

What <commit> can mean

When a command contains <commit>, several reference forms are available.

Form	Meaning	Example
Branch name	Commit currently targeted by that branch	main
Tag name	A release or marked location	v0.1
Commit ID	Hash prefix or complete hash for one commit	3e887ab
Remote branch	Current remote-tracking branch target	origin/main
HEAD	The currently checked-out commit	HEAD
HEAD^	Parent of the current commit	HEAD^
HEAD~3	Three first-parent steps before the current commit	HEAD~3

Notes:

• HEAD^^^ and HEAD~3 are common ways to trace three parent generations back.
• A merge commit has multiple parents, so ^ can take a number to choose a parent, such as HEAD^2.
• Before using an unfamiliar reference, inspect a graph with git log --oneline --graph --decorate.
• -- clearly separates commit/options from paths and avoids ambiguity when a branch and file share a name.

Minimum self-check

1. Which two layers do git diff, git diff --staged, and git diff HEAD compare?
2. Why preserve -- in git diff HEAD~1 -- README.md?
3. Why can HEAD^1 and HEAD^2 of a merge commit target different parents?