Recovering lost commits with reflog in Git - Mini Project: Build & Apply

Recovering Lost Commits with Reflog

📖 Scenario: You accidentally deleted some commits in your Git repository. You want to recover those lost commits using Git's reflog feature.

🎯 Goal: Learn how to use git reflog to find lost commits and restore your branch to a previous state.

📋 What You'll Learn

Use git reflog to view recent HEAD changes

Identify the commit hash of the lost commit

Use git reset --hard <commit-hash> to restore the branch

Verify the branch points to the recovered commit

💡 Why This Matters

🌍 Real World

Developers often accidentally lose commits by resetting branches or deleting branches. Using reflog helps recover those commits quickly without losing work.

💼 Career

Knowing how to recover lost commits is a valuable skill for software developers and DevOps engineers to maintain code integrity and avoid data loss.

1

Initialize a Git repository and create commits

Run git init to create a new Git repository. Then create a file named file.txt with the content First line. Add and commit this file with the message Initial commit. Next, append Second line to file.txt, add and commit with the message Second commit.

Git

# Run git commands to initialize repo and create two commits
# Your code here

Hint

Use git init to start a repo. Use echo to write to files. Use git add and git commit to save changes.

2

Simulate losing commits by resetting branch

Use git log --oneline to find the commit hash of the Initial commit. Then run git reset --hard <initial-commit-hash> to move the branch back to the first commit, losing the second commit from the branch history.

Git

git init

echo "First line" > file.txt

git add file.txt

git commit -m "Initial commit"

echo "Second line" >> file.txt

git add file.txt

git commit -m "Second commit"

# Use git reset --hard with the initial commit hash below
# Your code here

Hint

Use git log --oneline to get short commit hashes. Use shell commands to extract the hash. Then reset hard to that hash.

3

Use reflog to find lost commit hash

Run git reflog to see recent HEAD changes. Identify the commit hash of the lost Second commit from the reflog output. Assign this hash to a variable named lost_commit using shell commands.

Git

git init

echo "First line" > file.txt

git add file.txt

git commit -m "Initial commit"

echo "Second line" >> file.txt

git add file.txt

git commit -m "Second commit"

initial_commit_hash=$(git log --oneline | tail -1 | cut -d' ' -f1)

git reset --hard $initial_commit_hash

# Use git reflog and shell commands to assign lost commit hash to lost_commit
# Your code here

Hint

Use git reflog and grep to find the commit message. Extract the commit hash with cut or awk.

4

Restore the lost commit using reset

Use git reset --hard $lost_commit to restore the branch to the lost commit. Then run git log --oneline -1 to print the latest commit message and verify it is Second commit.

Git

git init

echo "First line" > file.txt

git add file.txt

git commit -m "Initial commit"

echo "Second line" >> file.txt

git add file.txt

git commit -m "Second commit"

initial_commit_hash=$(git log --oneline | tail -1 | cut -d' ' -f1)

git reset --hard $initial_commit_hash

lost_commit=$(git reflog | grep "Second commit" | head -1 | awk '{print $1}')

# Reset hard to lost_commit and print latest commit message
# Your code here

Hint

Use git reset --hard $lost_commit to restore. Use git log --oneline -1 --pretty=%s to print the commit message only.

Practice

1. What is the primary purpose of git reflog in Git?

easy

A. To show a log of where HEAD and branch references have been recently

B. To permanently delete commits from the repository

C. To merge two branches automatically

D. To push commits to a remote repository

Solution

1. Step 1: Understand what reflog tracks

   Git reflog records changes to HEAD and branch tips, showing recent commit movements.

2. Step 2: Identify reflog's main use

   It helps find lost commits by listing recent HEAD positions, not deleting or merging.

3. Final Answer:

   To show a log of where HEAD and branch references have been recently -> Option A

4. Quick Check:

   Reflog = recent HEAD changes [OK]

Hint: Reflog shows recent HEAD moves, not branch merges or deletions [OK]

Common Mistakes:

• Confusing reflog with git log
• Thinking reflog deletes commits
• Assuming reflog pushes commits

2. Which command correctly recovers a lost commit using its reflog hash abc1234 by creating a new branch named recovered?

easy

A. git branch recovered && git checkout abc1234

B. git reset --hard recovered abc1234

C. git reflog checkout abc1234 recovered

D. git checkout -b recovered abc1234

Solution

1. Step 1: Understand how to create a branch from a commit hash

   The command git checkout -b <branch> <commit> creates and switches to a new branch at that commit.

2. Step 2: Check each option's correctness

   git checkout -b recovered abc1234 uses correct syntax. git branch recovered && git checkout abc1234 creates branch but checks out commit separately (detached HEAD). git reflog checkout abc1234 recovered is invalid syntax. git reset --hard recovered abc1234 misuses reset.

3. Final Answer:

   git checkout -b recovered abc1234 -> Option D

4. Quick Check:

   Create branch from commit: checkout -b [OK]

Hint: Use 'git checkout -b branch commit' to recover lost commit [OK]

Common Mistakes:

• Using git reflog checkout (invalid command)
• Creating branch and checkout separately causing detached HEAD
• Misusing git reset syntax

3. Given the following reflog output snippet:

abc1234 HEAD@{0}: commit: Fix typo
def5678 HEAD@{1}: commit: Add feature
789abcd HEAD@{2}: commit: Initial commit

What command will restore the commit with message 'Add feature'?

medium

A. git checkout HEAD@{2}

B. git checkout 789abcd

C. git checkout def5678

D. git checkout abc1234

Solution

1. Step 1: Identify the commit hash for 'Add feature'

   From reflog, 'Add feature' commit hash is def5678 at HEAD@{1}.

2. Step 2: Use git checkout with the correct hash

   Checking out def5678 restores that commit state.

3. Final Answer:

   git checkout def5678 -> Option C

4. Quick Check:

   Checkout commit by hash = def5678 [OK]

Hint: Match commit message to hash, then checkout that hash [OK]

Common Mistakes:

• Choosing wrong commit hash
• Using HEAD@{2} which is 'Initial commit'
• Confusing latest commit with target commit

4. You ran git reflog and found a lost commit hash abc1234. You tried git checkout abc1234 but got a detached HEAD warning. How do you fix this to recover the commit safely?

medium

A. Create a new branch at that commit using git checkout -b recovered abc1234

B. Run git reset --hard abc1234 immediately

C. Delete the reflog entry and try again

D. Push the commit hash to remote

Solution

1. Step 1: Understand detached HEAD state

   Checking out a commit hash puts you in detached HEAD, which is risky for new work.

2. Step 2: Create a branch to save the commit safely

   Use git checkout -b recovered abc1234 to create a branch and avoid losing commits.

3. Final Answer:

   Create a new branch at that commit using git checkout -b recovered abc1234 -> Option A

4. Quick Check:

   Fix detached HEAD by creating branch [OK]

Hint: Always create a branch from lost commit to avoid detached HEAD [OK]

Common Mistakes:

• Ignoring detached HEAD and continuing work
• Deleting reflog entries mistakenly
• Trying to push without branch

5. You accidentally reset your branch to an older commit, losing recent commits. You run git reflog and see:

abc1234 HEAD@{0}: reset: moving to abc1234
def5678 HEAD@{1}: commit: Add new feature
789abcd HEAD@{2}: commit: Fix bug

How do you restore your branch to include the lost 'Add new feature' commit?

hard

A. Delete reflog entries before abc1234

B. Run git reset --hard def5678 to move branch back to lost commit

C. Run git checkout abc1234 to stay at reset point

D. Run git merge def5678 from abc1234

Solution

1. Step 1: Identify lost commit hash from reflog

   The lost commit 'Add new feature' is at def5678 (HEAD@{1}).

2. Step 2: Use git reset to move branch pointer back

   Running git reset --hard def5678 restores branch to that commit, recovering lost work.

3. Final Answer:

   Run git reset --hard def5678 to move branch back to lost commit -> Option B

4. Quick Check:

   Reset branch to lost commit hash [OK]

Hint: Use git reset --hard with reflog hash to recover lost commits [OK]

Common Mistakes:

• Checking out reset commit instead of resetting branch
• Deleting reflog entries unnecessarily
• Trying to merge without branch pointer