Viewing Commit History

Viewing commit history in Git is crucial for tracking changes, understanding the evolution of your codebase, and debugging. Here’s a detailed guide on how to view commit history using Git:

1. Basic Command

git log

The git log command shows the commit history for the current branch. By default, it displays the commits in reverse chronological order (most recent first).

Usage:

git log

Output Example:

commit 9a1b2c3d4e5f67890abcdef1234567890abcdef
Author: John Doe <johndoe@example.com>
Date:   Tue Aug 13 14:37:08 2024 +0000

    Fix issue with user login

commit 1234567890abcdef1234567890abcdef12345678
Author: Jane Smith <janesmith@example.com>
Date:   Mon Aug 12 09:15:22 2024 +0000

    Add new feature for data export

Each entry includes the commit hash, author, date, and commit message.

2. Customizing the Output

You can customize how git log displays information using various options:

• One line per commit:

  git log --oneline
  

• Graph view (shows a graphical representation of branches and merges):

  git log --graph
  

• Show commits with a specific keyword in the message:

  git log --grep="keyword"
  

• Limit the number of commits shown:

  git log -n 5
  

• Show commits by a specific author:

  git log --author="Author Name"
  

3. Viewing Detailed Commit Information

To view more detailed information about a specific commit, including the changes made:

Find the commit hash using git log and then:

git show <commit-hash>

Usage:

git show 9a1b2c3d4e5f67890abcdef1234567890abcdef

Output Example:

commit 9a1b2c3d4e5f67890abcdef1234567890abcdef
Author: John Doe <johndoe@example.com>
Date:   Tue Aug 13 14:37:08 2024 +0000

    Fix issue with user login

diff --git a/login.py b/login.py
index 1234567..89abcdef 100644
--- a/login.py
+++ b/login.py
@@ -1,5 +1,5 @@
 def login(username, password):
-    if username and password:
+    if username and password == "secure":
         return True
     return False

This displays the commit message, author, date, and the differences introduced in the commit.

4. Viewing History of a Specific File

To see the commit history for a specific file:

git log <file-path>

Usage:

git log path/to/your/file.txt

Output Example:

commit 9a1b2c3d4e5f67890abcdef1234567890abcdef
Author: John Doe <johndoe@example.com>
Date:   Tue Aug 13 14:37:08 2024 +0000

    Fix issue with user login

diff --git a/file.txt b/file.txt

This shows all commits that modified the specified file.

5. Using Git Log with Filters

You can combine various options to filter and format the log output:

• Show commits within a specific date range:

  git log --since="2024-08-01" --until="2024-08-10"
  

• Show commits by a specific path and format the output:

  git log --pretty=format:"%h - %an, %ar : %s" -- path/to/file
  

Summary

By mastering these commands and options, you can efficiently navigate and understand your Git commit history, which is essential for managing and collaborating on code projects.