git diff --staged for staged changes - Commands & Configuration

Introduction

Sometimes you want to see what changes you have prepared to save before actually saving them. The command git diff --staged shows the differences between the last saved version and what you have marked to save next.

When you want to review the exact changes you have marked to save before making the save permanent.

When you accidentally staged some files and want to check what changes are included.

When you want to compare your staged changes with the last saved version to ensure correctness.

When you are preparing a save and want to double-check what will be included.

When you want to see the difference between your staged files and the last commit.

Commands

This command marks the file example.txt to be saved in the next commit. It moves changes from unstaged to staged.

Terminal

git add example.txt

Expected Output

No output (command runs silently)

This command shows the differences between the last saved version and the files you have staged to save next. It helps you review staged changes.

Terminal

git diff --staged

Expected Output

diff --git a/example.txt b/example.txt

index e69de29..d95f3ad 100644

--- a/example.txt

+++ b/example.txt

@@ -0,0 +1,2 @@

+Hello, this is a new line.

+Another added line.

→

--staged - Shows differences for staged files compared to the last commit.

Key Concept

If you remember nothing else from this pattern, remember: git diff --staged shows exactly what changes are ready to be saved next.

Common Mistakes

Running git diff without --staged to see staged changes.

git diff without --staged only shows unstaged changes, so you miss what is staged.

Use git diff --staged to see changes that are staged and ready to be saved.

Expecting git diff --staged to show unstaged changes.

It only shows staged changes, so unstaged changes are not visible.

Use git diff alone to see unstaged changes.

Summary

Use git add to stage changes you want to save.

Use git diff --staged to review what staged changes will be saved.

This helps avoid mistakes by confirming staged content before committing.

Practice

1. What does the command git diff --staged show?

easy

A. Changes that are staged and ready to be committed

B. All changes in the working directory, staged or not

C. The commit history of the repository

D. Untracked files in the repository

Solution

1. Step 1: Understand what staging means in Git

   Staging means preparing changes to be saved in the next commit.

2. Step 2: Identify what git diff --staged compares

   This command compares the staged changes against the last commit, showing what will be committed.

3. Final Answer:

   Changes that are staged and ready to be committed -> Option A

4. Quick Check:

   Staged changes = git diff --staged output [OK]

Hint: Remember: --staged shows only prepared changes [OK]

Common Mistakes:

• Confusing staged changes with all changes
• Thinking it shows commit history
• Assuming it lists untracked files

2. Which of the following is the correct syntax to view staged changes using git?

easy

A. git diff staged

B. git diff --cached

C. git diff --stage

D. git diff --status

Solution

1. Step 1: Recall git diff options for staged changes

   Git uses --cached as the official option to show staged changes.

2. Step 2: Understand that --staged is an alias

   --staged is a common alias but --cached is the correct and original syntax.

3. Final Answer:

   git diff --cached -> Option B

4. Quick Check:

   Correct syntax for staged diff = git diff --cached [OK]

Hint: Use --cached to view staged changes reliably [OK]

Common Mistakes:

• Using incorrect flags like --stage
• Omitting the double dash before options
• Confusing staged with unstaged flags

3. Given the following commands executed in order:

echo 'Hello' > file.txt
git add file.txt
git diff --staged

What will git diff --staged display?

medium

A. No output, because the file is new and staged

B. An error because the file is not committed yet

C. The difference showing removal of 'Hello' in file.txt

D. The difference showing the addition of 'Hello' in file.txt

Solution

1. Step 1: Understand the state of file.txt after commands

   The file is new with content 'Hello' and has been staged with git add.

2. Step 2: What does git diff --staged show here?

   It shows the difference between the staged version and the last commit (which has no file.txt), so it shows the addition of 'Hello'.

3. Final Answer:

   The difference showing the addition of 'Hello' in file.txt -> Option D

4. Quick Check:

   New staged file diff shows added content [OK]

Hint: New staged files show additions in git diff --staged [OK]

Common Mistakes:

• Expecting no output for new files
• Thinking git diff --staged errors on new files
• Confusing removal with addition

4. You modified files in your editor, staged them with git add, ran git diff --staged but saw no output. What could be the problem?

medium

A. You staged the files but forgot to save changes in the editor

B. You used git diff instead of git diff --staged

C. You committed the changes already, so no staged changes remain

D. The repository has no commits yet

Solution

1. Step 1: Check if file changes are saved before staging

   If changes are not saved in the editor, staging old content means no visible diff.

2. Step 2: Understand why no output appears

   Since staged content matches last commit (or is empty), git diff --staged shows nothing.

3. Final Answer:

   You staged the files but forgot to save changes in the editor -> Option A

4. Quick Check:

   Unsaved edits cause empty staged diff [OK]

Hint: Always save files before staging to see diffs [OK]

Common Mistakes:

• Assuming git diff --staged shows unstaged changes
• Not realizing files were not saved
• Thinking commit status affects staged diff output

5. You have staged changes in two files: app.js and index.html. You want to see only the staged changes in app.js. Which command should you use?

hard

A. git diff --cached index.html

B. git diff app.js staged

C. git diff --staged app.js

D. git diff --staged --name-only app.js

Solution

1. Step 1: Understand how to limit git diff to a specific file

   You can specify the file path after the options to filter the diff output.

2. Step 2: Choose the correct syntax for staged changes and file filter

   git diff --staged app.js correctly shows staged changes only for app.js.

3. Final Answer:

   git diff --staged app.js -> Option C

4. Quick Check:

   File filter after --staged shows staged diff for that file [OK]

Hint: Put filename after --staged to filter staged diff [OK]

Common Mistakes:

• Placing filename before options
• Using --name-only which lists files, not diffs
• Mixing staged and unstaged file filters