Brief Overview

On Day 3, we will cover:

1. Understanding the importance of Git history.

2. Using git log to view commit history.

3. Customizing git log output.

4. Viewing changes with git diff.

5. Exploring specific commits with git show.

Detailed Explanation with Code

1. Understanding the Importance of Git History: The Git history is a record of all the commits made to a repository. It helps track changes, understand the evolution of the project, and identify who made specific changes. Reviewing the history is crucial for debugging, collaboration, and maintaining a clean project.

2. Using git log to View Commit History: The git log command shows the commit history of the repository. Each commit includes information like the commit hash, author, date, and commit message.

    git log
   

   Example:

    git log
   

   Output:

    commit a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t
    Author: Your Name <youremail@example.com>
    Date:   Mon Jul 26 12:34:56 2023 +0000
   
        Update hello.txt with another new line
   
    commit d1e8d3b4c5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t
    Author: Your Name <youremail@example.com>
    Date:   Sun Jul 25 11:23:45 2023 +0000
   
        Add hello.txt with initial content
   

3. Customizing git log Output: The git log command can be customized to display information in various formats. Here are some useful options:

   • One-line Summary: Display each commit on a single line.

       git log --oneline
     

     Example:

       git log --oneline
     

     Output:

       a1b2c3d Update hello.txt with another new line
       d1e8d3b Add hello.txt with initial content
     

   • Graphical Representation: Show a graphical representation of the commit history.

       git log --graph --oneline
     

     Example:

       git log --graph --oneline
     

     Output:

       * a1b2c3d Update hello.txt with another new line
       * d1e8d3b Add hello.txt with initial content
     

   • Author and Date: Display the author and date of each commit.

       git log --pretty=format:"%h - %an, %ar : %s"
     

     Example:

       git log --pretty=format:"%h - %an, %ar : %s"
     

     Output:

       a1b2c3d - Your Name, 2 hours ago : Update hello.txt with another new line
       d1e8d3b - Your Name, 1 day ago : Add hello.txt with initial content
     

4. Viewing Changes with git diff: The git diff command shows the differences between various commits, working directory, and staging area.

   • Unstaged Changes: Show changes that haven't been staged yet.

       git diff
     

     Example:

       echo "Another change" >> hello.txt
       git diff
     

     Output:

       diff --git a/hello.txt b/hello.txt
       index 47eb3d1..1a2b3c4 100644
       --- a/hello.txt
       +++ b/hello.txt
       @@ -1,2 +1,3 @@
        Hello, Git!
        This is a new line.
       +Another change
     

   • Staged Changes: Show changes that have been staged but not yet committed.

       git diff --staged
     

     Example:

       git add hello.txt
       git diff --staged
     

     Output:

       diff --git a/hello.txt b/hello.txt
       index 47eb3d1..1a2b3c4 100644
       --- a/hello.txt
       +++ b/hello.txt
       @@ -1,2 +1,3 @@
        Hello, Git!
        This is a new line.
       +Another change
     

5. Exploring Specific Commits with git show: The git show command displays detailed information about a specific commit, including the commit message, author, date, and the changes introduced by the commit.

    git show <commit-hash>
   

   Example:

    git show a1b2c3d
   

   Output:

    commit a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t
    Author: Your Name <youremail@example.com>
    Date:   Mon Jul 26 12:34:56 2023 +0000
   
        Update hello.txt with another new line
   
    diff --git a/hello.txt b/hello.txt
    index 47eb3d1..1a2b3c4 100644
    --- a/hello.txt
    +++ b/hello.txt
    @@ -1,2 +1,3 @@
     Hello, Git!
     This is a new line.
    +Another change
   

Example Workflow

1. Initialize a New Git Repository:

    mkdir my-git-project
    cd my-git-project
    git init
   

2. Create and Commit a File:

    echo "Hello, Git!" > hello.txt
    git add hello.txt
    git commit -m "Add hello.txt with initial content"
   

3. Modify and Commit the File Again:

    echo "This is a new line." >> hello.txt
    git add hello.txt
    git commit -m "Update hello.txt with new content"
   

4. View the Commit History:

    git log
   

5. Customize the Commit History View:

    git log --oneline
    git log --graph --oneline
    git log --pretty=format:"%h - %an, %ar : %s"
   

6. View Differences Between Commits:

    echo "Another change" >> hello.txt
    git diff
    git add hello.txt
    git diff --staged
   

7. Show Detailed Information About a Specific Commit:

    git show a1b2c3d
   

By the end of Day 3, readers should understand how to view and interpret the commit history using various Git commands. This knowledge is essential for tracking changes, understanding the project's evolution, and collaborating effectively.