Git: Show Difference Between Files

Important Concepts

here's some important concepts of areas/states for diff to work on (All are local on your computer):

Working Directory (aka Working Tree)

Files in your project's directory.

Index (aka Staging Area)

A virtual area (a index file) that git add is placed into.

Commit ID

A specific commit. 〔see Git: Commit ID〕

HEAD

A variable that usually refers to the last commit of current branch. 〔see Git: What's HEAD〕

Diff workingDir vs lastCommit

git diff --color commitID

diff workingDir vs lastCommit. Replace the commitID by HEAD for lastCommit.

Diff Between 2 Commits

git diff ID1 ID2 filename

diff between 2 commits. 〔see Git: Commit ID〕

Diff workingDir vs Index

git diff --color

diff workingDir vs Index

git diff --color filename

diff workingDir vs Index, 1 file

Diff Index vs lastCommit

git diff --color --staged commitID

diff Index vs lastCommit

Show Changed Files

git status

Show state of {Index, workingDir, lastCommit}

2014-01-18 Thanks to Nick Alcock for review.