Why diffing matters in Git - See It in Action

Why Diffing Matters in Git

📖 Scenario: You are working on a small project with a friend. You both make changes to the same file. To understand what changed, you use Git's diff feature.

🎯 Goal: Learn how to use git diff to see changes between file versions and understand why diffing helps track changes in code.

📋 What You'll Learn

Create a file with initial content

Make a change to the file

Use git diff to see the changes

Understand the output of git diff

💡 Why This Matters

🌍 Real World

Diffing is like comparing two versions of a document to see what changed. It helps developers review code before sharing it.

💼 Career

Understanding diffing is essential for collaboration in software teams, code reviews, and managing changes safely.

1

Create a file with initial content

Create a file named notes.txt with the exact content: Hello World

Git

# Create the file notes.txt with content 'Hello World'
# Your code here

Hint

Use the echo command to write text to a file.

2

Make a change to the file

Add a new line with the text Welcome to Git to the file notes.txt

Git

echo "Hello World" > notes.txt
# Add a new line 'Welcome to Git' to notes.txt
# Your code here

Hint

Use >> to append text to a file.

3

Initialize Git and check the diff

Initialize a Git repository with git init and then run git diff to see the changes in notes.txt

Git

echo "Hello World" > notes.txt
echo "Welcome to Git" >> notes.txt
# Initialize git repository
# Run git diff to see changes
# Your code here

Hint

Use git init to start a repository and git diff to see unstaged changes.

4

Understand the diff output

Run git add notes.txt and then modify notes.txt by changing Hello World to Hello Git. Finally, run git diff to see the difference between the staged and unstaged changes.

Git

echo "Hello World" > notes.txt
echo "Welcome to Git" >> notes.txt
git init
git diff
# Add notes.txt to staging
# Change 'Hello World' to 'Hello Git' in notes.txt
# Run git diff to see unstaged changes
# Your code here

Hint

Use git add to stage changes and sed to replace text in the file.

Practice

1. What is the main purpose of using git diff in a project?

easy

A. To delete files from the repository

B. To create a new branch

C. To merge two branches automatically

D. To see the exact changes made between file versions

Solution

1. Step 1: Understand the function of git diff

   git diff shows differences between file versions or commits.

2. Step 2: Identify what git diff does not do

   It does not delete files, merge branches, or create branches.

3. Final Answer:

   To see the exact changes made between file versions -> Option D

4. Quick Check:

   Diffing = showing changes [OK]

Hint: Diff means showing changes between versions [OK]

Common Mistakes:

• Confusing diff with branch creation
• Thinking diff deletes files
• Assuming diff merges branches

2. Which of the following is the correct command to see unstaged changes in your working directory?

easy

A. git diff

B. git diff --staged

C. git status -s

D. git log

Solution

1. Step 1: Recall the meaning of git diff

   git diff shows unstaged changes in your working directory compared to the last commit.

2. Step 2: Understand other commands

   git diff --staged shows staged changes, git status -s shows status summary, and git log shows commit history.

3. Final Answer:

   git diff -> Option A

4. Quick Check:

   Unstaged changes = git diff [OK]

Hint: Use plain git diff for unstaged changes [OK]

Common Mistakes:

• Using git diff --staged for unstaged changes
• Confusing git status with diff output
• Using git log to see file changes

3. Given the following commands run in a git repository:

echo 'Hello' > file.txt
git add file.txt
echo 'World' >> file.txt
git diff

What will git diff show?

medium

A. The difference showing the addition of 'World' in file.txt

B. The entire content of file.txt

C. No output because all changes are staged

D. An error because file.txt is staged

Solution

1. Step 1: Analyze the commands

   First, 'Hello' is written and staged with git add. Then 'World' is appended but not staged.

2. Step 2: Understand what git diff shows

   git diff shows unstaged changes compared to the index (staged files). So it will show the addition of 'World'.

3. Final Answer:

   The difference showing the addition of 'World' in file.txt -> Option A

4. Quick Check:

   git diff = unstaged changes [OK]

Hint: git diff shows changes after last staging [OK]

Common Mistakes:

• Thinking git diff shows staged changes
• Expecting full file content output
• Assuming git diff errors on staged files

4. You ran git diff but it shows no output even though you edited a file. What is the most likely reason?

medium

A. You forgot to save the file after editing

B. You staged the changes with git add

C. You are on the wrong branch

D. The file is ignored by .gitignore

Solution

1. Step 1: Understand what git diff shows

   git diff shows unstaged changes in saved files.

2. Step 2: Consider why no changes appear

   If the changes are staged with git add, git diff shows no output because there are no unstaged changes.

3. Final Answer:

   You staged the changes with git add -> Option B

4. Quick Check:

   Staged changes = no unstaged diff output [OK]

Hint: Stage changes to clear unstaged diff output [OK]

Common Mistakes:

• Assuming staged changes show in git diff
• Thinking branch affects unstaged diff
• Confusing ignored files with unstaged changes

5. You want to review changes between two commits abc123 and def456. Which command correctly shows the differences?

hard

A. git diff --compare abc123..def456

B. git diff --staged abc123 def456

C. git diff abc123..def456

D. git diff --between abc123 def456

Solution

1. Step 1: Recall correct syntax for comparing commits

   The correct syntax uses two commit hashes separated by two dots: git diff abc123..def456.

2. Step 2: Identify invalid options

   git diff --staged abc123 def456 is invalid syntax, and options with --between or --compare do not exist.

3. Final Answer:

   git diff abc123..def456 -> Option C

4. Quick Check:

   Commit range uses two dots [OK]

Hint: Use two dots between commits for diff [OK]

Common Mistakes:

• Using git diff --staged for commit diffs
• Adding unsupported flags like --between
• Confusing diff syntax with log syntax