Git Diff: Compare Changes Across Commits and Branches

What Git Diff Shows

`git diff` shows the differences between two states of your repository — unstaged changes, staged changes, commits, or branches.

# Unstaged changes (working directory vs staging)

git diff

# Staged changes (staging vs last commit)

git diff --staged

# All changes (unstaged + staged)

git diff HEAD

Comparing Commits

# Between two commits

git diff abc1234..def5678

# Between a commit and HEAD

git diff HEAD~3..HEAD

# Just the files that changed (no content)

git diff --name-only HEAD~3..HEAD

Comparing Branches

# What's different between main and feature

git diff main..feature

# What feature has that main doesn't:

git diff main...feature

# (three dots = changes on feature since it diverged from main)

Reading Diff Output

diff --git a/src/app.ts b/src/app.ts

--- a/src/app.ts

+++ b/src/app.ts

@@ -10,6 +10,8 @@

const port = 3000;

+const host = "0.0.0.0";

app.listen(port);

Red lines with `-` are removed, green lines with `+` are added. The `@@` line shows the file position.

Useful Diff Options

# Ignore whitespace

git diff -w

# Show word-level changes (not line-level)

git diff --word-diff

# Show stats only

git diff --stat

# Generate a patch file

git diff > changes.patch

Diff in Review Workflows

Use `git diff` before every commit to catch unintended changes. It is the fastest code review tool you have — it runs locally, shows exactly what you are about to commit, and takes seconds.