Now that you have a Git repository set up, it's time to learn how to track changes to your files. This section covers checking status, staging changes, creating commits, and viewing your history.

Checking Repository Status

Before making changes, it's good practice to check the status of your repository:

git status

This shows which files are tracked, untracked, modified, or staged. It's one of the most used Git commands and gives you a clear picture of what's happening in your repository.

Tracking New Files

When you create new files in your repository, Git won't track them automatically. To start tracking a new file:

git add filename.txt

To add multiple files:

git add file1.txt file2.txt file3.txt

Or to add all files in the current directory and its subdirectories:

git add .

This stages the files for commit. You can verify this with git status, which will now show the files under "Changes to be committed".

Understanding the Staging Area

The staging area (or "index") is a crucial concept in Git. It's a preparation area where you organize what will go into your next commit.

Think of it as a loading dock where you prepare goods for shipping. You can:

Add files to the staging area (git add)
Remove files from the staging area (git reset)
Review what's in the staging area (git status)

Staging lets you commit only some changes while keeping others for a different commit, allowing you to create clean, logical commits.

Staging Parts of a File

Sometimes you only want to stage some changes in a file, not all of them. You can do this with:

git add -p filename.txt

This will interactively ask you which parts ("hunks") of the file to stage, giving you options like:

y: stage this hunk
n: don't stage this hunk
s: split the hunk into smaller hunks
q: quit, don't stage this or any remaining hunks
?: display help

Making Commits

Once you've staged your changes, you can commit them to your repository:

git commit -m "Add initial project files"

The -m flag allows you to add a commit message directly on the command line. Your message should briefly describe the changes in the commit.

For more detailed commit messages, omit the -m flag:

git commit

This opens your configured text editor where you can write a more detailed message.

Good Commit Message Practices

A good commit message follows these guidelines:

Short, descriptive summary line (50 characters or less)
Optional blank line followed by a more detailed explanation
Written in imperative mood ("Add feature", not "Added feature")
Explains what and why, not how (the code shows how)

Example of a good commit message:

Add user authentication feature

- Implement login/logout functionality
- Set up password hashing with bcrypt
- Add session management

This addresses security requirements in issue #42

Shortcuts for Staging and Committing

To stage and commit all modified files in one step:

git commit -a -m "Update configuration files"

The -a flag automatically stages all modified tracked files (but not new files).

Viewing Changes

To see what changes you've made but haven't staged yet:

git diff

To see what you've staged that will go into your next commit:

git diff --staged

These commands show the exact lines added and removed, which is helpful for reviewing your changes before committing them.

Removing Files

To remove a file from Git and your working directory:

git rm filename.txt

To remove a file from Git but keep it in your working directory (useful for files you accidentally started tracking):

git rm --cached filename.txt

Don't forget to add the file to your .gitignore if you want to keep it untracked.

Moving and Renaming Files

To move or rename a file:

git mv old_filename.txt new_filename.txt

This is equivalent to:

mv old_filename.txt new_filename.txt
git rm old_filename.txt
git add new_filename.txt

Viewing Commit History

To see the history of your commits:

git log

This displays each commit with its:

SHA-1 checksum (unique identifier)
Author name and email
Date and time
Commit message

For a more concise view:

git log --oneline

Or to see changes in each commit:

git log -p

To see statistics for each commit:

git log --stat

To visualize the commit history with a graph:

git log --graph --oneline --all

Undoing Things

Git provides several ways to undo changes:

Amending the Last Commit

If you've made a mistake in your last commit or forgot to include some changes:

git commit --amend

This replaces the last commit with a new one that includes both the changes from the previous commit and any staged changes you have now.

Unstaging Files

If you've staged a file but want to unstage it:

git restore --staged filename.txt

In older Git versions:

git reset HEAD filename.txt

Discarding Changes

To discard changes in your working directory and revert to the last committed version:

git restore filename.txt

In older Git versions:

git checkout -- filename.txt

⚠️ Warning: This operation cannot be undone. Any local changes will be lost.

Tagging

Tags are references that point to specific points in Git history, typically used to mark release versions.

To create a lightweight tag:

git tag v1.0.0

To create an annotated tag with a message:

git tag -a v1.0.0 -m "Version 1.0.0 release"

To list all tags:

git tag

To show information about a specific tag:

git show v1.0.0

By mastering these fundamental Git commands for tracking changes, you'll be able to maintain a clean and well-documented history of your project. In the next section, we'll explore branching, which enables you to work on multiple features or fixes in parallel.