How Git stores objects - Practice Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What type of Git object stores the content of a file?

In Git, different objects store different data. Which type of object stores the actual content of a file?

A Tag

B Blob

C Commit

D Tree

💡 Hint

Think about the object that holds raw file data without metadata.

A blob object stores the content of a file in Git. It does not contain file names or directory info.

💻 Command Output

intermediate

What is the output of 'git cat-file -t ' for a commit object?

You run the command git cat-file -t <object_hash> where <object_hash> is a commit object hash. What output do you expect?

A commit

B blob

C tree

D tag

💡 Hint

This command shows the type of the object by its hash.

The command git cat-file -t prints the type of the object. For a commit object, it prints commit.

❓ Configuration

advanced

How to verify the SHA-1 hash of a file matches its Git blob object?

You want to check if a file's content matches a Git blob object hash. Which command correctly computes the SHA-1 hash Git uses for blobs?

Git

echo -n "$(wc -c < file.txt)" | cat - file.txt | git hash-object --stdin

A git hash-object --stdin < file.txt

B sha1sum file.txt

C git hash-object file.txt

D git hash-object --stdin -w < file.txt

💡 Hint

Git hashes the file content with a header internally.

git hash-object file.txt computes the SHA-1 hash of the file content as Git stores it in a blob object.

❓ Troubleshoot

advanced

Why does 'git cat-file -p ' fail with 'fatal: Not a valid object name'?

You run git cat-file -p <hash> but get the error fatal: Not a valid object name. What is the most likely cause?

A The command requires root privileges

B The hash is a valid commit but corrupted

C The repository is not initialized

D The hash does not exist in the repository

💡 Hint

Check if the object hash is correct and present in the repo.

This error means Git cannot find the object with the given hash in the repository.

🔀 Workflow

expert

Order the steps Git uses to store a new file as an object

Put these steps in the correct order for how Git stores a new file as a blob object.

A 1,2,4,3

B 1,2,3,4

C 1,4,2,3

D 4,1,2,3

💡 Hint

Think about hashing, compressing, creating object, then writing to disk.

Git first calculates the hash, then compresses the data, creates the blob object, and finally writes it to the objects directory.

Practice

1. What type of Git object stores the actual content of a file?

easy

A. Blob

B. Tree

C. Commit

D. Tag

Solution

1. Step 1: Understand Git object types

   Git stores data in objects: blobs for file content, trees for directories, commits for snapshots, and tags for references.

2. Step 2: Identify the object for file content

   The blob object specifically holds the content of files, not metadata or history.

3. Final Answer:

   Blob -> Option A

4. Quick Check:

   File content = Blob [OK]

Hint: Remember: Blob = file content, Tree = folder [OK]

Common Mistakes:

• Confusing tree with blob
• Thinking commit stores file content
• Assuming tag stores file data

2. Which command correctly shows the type of a Git object given its hash abc123?

easy

A. git object-type abc123

B. git show-type abc123

C. git cat-file -t abc123

D. git object -show abc123

Solution

1. Step 1: Recall Git commands for object info

   The command git cat-file is used to inspect Git objects. The -t option shows the object type.

2. Step 2: Match the correct syntax

   git cat-file -t abc123 correctly shows the type of the object with hash abc123. Other options are invalid commands.

3. Final Answer:

   git cat-file -t abc123 -> Option C

4. Quick Check:

   Show object type = git cat-file -t [OK]

Hint: Use git cat-file -t to check object type fast [OK]

Common Mistakes:

• Using git show-type which doesn't exist
• Confusing git object commands
• Forgetting the -t option

3. Given a Git commit object hash def456, what will the command git cat-file -p def456 display?

medium

A. The raw content of a file stored in the commit

B. The list of branches containing the commit

C. The tags pointing to this commit

D. The commit message, author info, and tree hash

Solution

1. Step 1: Understand what a commit object contains

   A commit object stores metadata: author, date, commit message, and a tree hash representing the snapshot of files.

2. Step 2: Interpret git cat-file -p output for commit

   The command git cat-file -p pretty-prints the commit object, showing its message, author info, and tree hash, not raw file content or branch/tag info.

3. Final Answer:

   The commit message, author info, and tree hash -> Option D

4. Quick Check:

   Commit object details = message + author + tree [OK]

Hint: Commit object shows metadata, not file content [OK]

Common Mistakes:

• Expecting file content from commit object
• Confusing branches or tags with commit data
• Thinking commit object lists branches

4. You run git cat-file -p 123abc but get an error: fatal: Not a valid object name 123abc. What is the most likely cause?

medium

A. The command syntax is incorrect

B. The hash 123abc does not exist in the repository

C. You need to add files before using git cat-file

D. The repository is corrupted

Solution

1. Step 1: Analyze the error message

   The error says the object name is invalid, meaning Git cannot find an object with hash 123abc.

2. Step 2: Check common causes

   This usually happens if the hash is wrong or does not exist. The command syntax is correct, and adding files is unrelated. Repository corruption is less common and would cause other errors.

3. Final Answer:

   The hash 123abc does not exist in the repository -> Option B

4. Quick Check:

   Invalid object name = missing hash [OK]

Hint: Check if object hash exists before using git cat-file [OK]

Common Mistakes:

• Assuming syntax error instead of missing object
• Thinking files must be added before cat-file
• Jumping to repository corruption conclusion

5. You want to find the SHA-1 hash of a file's content before committing. Which Git command sequence correctly creates the object and shows its hash without committing?

hard

A. git hash-object -w <file> && git cat-file -p <hash>

B. git commit -m 'temp' && git show <file>

C. git add <file> && git log --hash

D. git init && git status

Solution

1. Step 1: Understand git hash-object usage

   The command git hash-object -w <file> creates a blob object from the file content and writes it to the object database, returning its hash.

2. Step 2: Verify object content with git cat-file

   Using git cat-file -p <hash> shows the content of the created blob object, confirming the hash matches the file content.

3. Final Answer:

   git hash-object -w <file> && git cat-file -p <hash> -> Option A

4. Quick Check:

   hash-object -w creates blob and shows hash [OK]

Hint: Use git hash-object -w to create and get file hash [OK]

Common Mistakes:

• Using git commit before hashing
• Confusing git add with hashing
• Thinking git init shows file hash