SHA-1 hashing concept in Git - Commands & Configuration

Introduction

SHA-1 hashing creates a unique code for data to identify it easily. It helps Git track changes and find files quickly without storing duplicates.

When you want to check the unique ID of a file or commit in Git.

When Git needs to verify if a file has changed or stayed the same.

When you want to see the commit history with unique commit IDs.

When you want to share a specific commit by its unique SHA-1 hash.

When Git stores objects like commits, trees, and blobs using SHA-1 hashes.

Commands

This command creates a new Git repository named 'my-repo' to start tracking files and changes.

Terminal

git init my-repo

Expected Output

Initialized empty Git repository in /home/user/my-repo/.git/

Change directory into the new repository to work inside it.

Terminal

cd my-repo

Expected Output

No output (command runs silently)

Create a new file named 'file.txt' with the text 'Hello Git' to add to the repository.

Terminal

echo "Hello Git" > file.txt

Expected Output

No output (command runs silently)

Stage the new file so Git knows to include it in the next commit.

Terminal

git add file.txt

Expected Output

No output (command runs silently)

Create a commit that saves the current state of the repository with a message describing the change.

Terminal

git commit -m "Add file.txt with greeting"

Expected Output

[main (root-commit) 1a2b3c4] Add file.txt with greeting

 1 file changed, 1 insertion(+)

 create mode 100644 file.txt

→

-m - Adds a commit message inline without opening an editor

Show the commit history with short SHA-1 hashes and commit messages to identify commits quickly.

Terminal

git log --oneline

Expected Output

1a2b3c4 Add file.txt with greeting

→

--oneline - Displays each commit in a single line with short SHA-1 hash

Calculate and show the full SHA-1 hash of the file content to see its unique identifier in Git.

Terminal

git hash-object file.txt

Expected Output

3b18e7a2a1f4c9d5e6f7a8b9c0d1e2f3a4b5c6d7

Key Concept

If you remember nothing else from this pattern, remember: Git uses SHA-1 hashes to uniquely identify and track every file and commit.

Common Mistakes

Trying to use SHA-1 hashes without committing files first

No commits or objects exist yet, so Git cannot show hashes for them

Add and commit files before checking their SHA-1 hashes

Confusing full SHA-1 hashes with short hashes shown in logs

Short hashes are abbreviations and may not be unique in large repos

Use full SHA-1 hashes when exact identification is needed

Summary

Initialize a Git repository to start tracking files.

Add and commit files to create objects identified by SHA-1 hashes.

Use git log and git hash-object to view SHA-1 hashes for commits and files.