1. First, Understand Git’s “Three Areas”¶

Before understanding the staging area, we need to know the key areas in Git, which act like “different state zones for files”:

1. Working Directory
   This is where your current files are located, such as code files in VS Code or documents in Notepad. All your file modifications (additions, deletions, edits) happen here.

2. Staging Area
   A temporary “transfer station,” like a courier hub. When you want to commit changes from the working directory to the repository, you first move the modified files to the staging area, which temporarily saves these changes, allowing you to review and adjust them.

3. Local Repository
   The actual “warehouse,” storing all historical versions of your commits. Each commit operation saves the contents of the staging area into the local repository, creating a new version.

2. Why Git Requires add Before commit?¶

The core reason is: The staging area acts as a “filter” before committing, giving you flexibility to control “what to commit”. Without the staging area, a direct commit would submit all changes from the working directory, leading to two issues:
- You might commit incomplete work (e.g., unfinished code, which would require reverting the entire version later).
- You cannot commit changes in stages (e.g., you want to submit Feature A first, then Feature B, but if both are modified together, you have to submit them all at once, cluttering the commit history).

3. The Staging Area’s “Transfer Station” Role¶

Let’s use an example to clarify:
Suppose you’re writing a novel and want to submit it in two parts: “Chapter 1” and “Chapter 2”.

1. Write Chapter 1: After completing it in the working directory (but not ready to submit yet, maybe for polishing), run git add chapter1.md to move “Chapter 1” to the staging area (transfer station).
2. Check the Staging Area: Use git status to see that “chapter1.md” is in the staging area, while “Chapter 2” remains in the working directory.
3. Commit Chapter 1: Execute git commit -m "Completed Chapter 1", and the staging area’s “Chapter 1” is now committed to the local repository, creating the first version.
4. Continue Writing Chapter 2: After finishing in the working directory, run git add chapter2.md to stage it, then commit to create the second version.

Without the staging area, you’d have to write the entire novel at once, making it impossible to submit in stages or undo incomplete work.

4. Key Operations: Differences Between add and commit¶

• git add: Adds changes from the working directory to the staging area.
• Syntax: git add <filename> (single file) or git add . (all modified files).

• Example: git add hello.txt stages all changes to hello.txt in the working directory.

• git commit: Submits the contents of the staging area to the local repository.

• Syntax: git commit -m "Commit message" (the message should clearly describe the changes).
• Example: git commit -m "Fix login bug" submits all staged changes to the repository, creating a new version.

5. Common Issue: What Happens If You commit Without add?¶

If you modify files in the working directory but skip add, what happens?

• Case 1: git commit will prompt “nothing to commit” because the staging area is empty.
• Case 2: To force commit all working directory changes (not recommended), use git commit -a -m "message". However, -a commits all tracked files (already managed by Git), which may include unready modifications.

6. Undoing Staged Changes¶

If you accidentally stage a file you don’t want, or need to rework staged content, use git reset HEAD <filename> to move a file from the staging area back to the working directory:
- Example: git reset HEAD hello.txt removes hello.txt from the staging area, returning it to the “modified but not staged” state.

Summary: The Value of the Staging Area¶

The staging area in Git is like a “draft box” that lets you:
- Commit in stages: Submit only what you want, avoiding “submitting incomplete work.”
- Review changes: Use git status to verify staging area contents before committing, ensuring no accidental submissions.
- Adjust flexibly: Undo staging (with reset) and rework changes before re-adding, preventing “unrecoverable mistakes.”

Thus, add before commit is a core Git design, ensuring clear version history and preventing accidental submissions. Remember: The staging area is the “final checkpoint before commit”—only changes passing this checkpoint are safely committed to the repository.