Viewing Commit History (git log)

Git projects build a history by saving significant changes as commits. To effectively manage and review your work, understanding how to view this history is essential. The git log command provides a powerful way to look back at all the changes you've saved. Consider git log as your project's detailed journal, chronicling every commit.

Running the git log command in your terminal, within your repository directory, will display a chronological list of commits, starting with the most recent one.

cd your-repo-directory
git log

The output for each commit typically looks something like this:

commit a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0 (HEAD -> main)
Author: Your Name <[email protected]>
Date:   Tue May 21 10:30:00 2024 +0000

    Initial commit: Add project structure

commit f9e8d7c6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0
Author: Your Name <[email protected]>
Date:   Tue May 21 09:45:15 2024 +0000

    Add README file

Let's break down the information presented for each commit:

• Commit Hash: The long string of letters and numbers (e.g., a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0) is the commit's unique identifier, technically a SHA-1 hash. This ID guarantees the integrity of the commit and allows Git (and you) to refer to specific points in history. You usually only need the first 7-10 characters to uniquely identify a commit in practice. The (HEAD -> main) part indicates that HEAD (your current position in the project history) is pointing to the main branch, and this commit is the latest one on that branch. We'll discuss branches and HEAD more later.
• Author: This shows the name and email address of the person who originally wrote the changes. This information comes from the user.name and user.email configuration you set up earlier.
• Date: The timestamp indicates when the commit was created.
• Commit Message: This is the descriptive message you provided when you ran git commit -m "Your message". As you can see, clear messages (like discussed in "Writing Good Commit Messages") make the log much more informative.

Customizing the Log Output

The default git log output is informative, but it can be quite verbose, especially as your project grows. Git offers many options to customize the output to show precisely what you need. Here are a few common and useful ones:

Concise Summary with --oneline

To get a very compact view, use the --oneline option. It shows only the first part of the commit hash and the commit message subject line for each commit:

git log --oneline

Output:

a1b2c3d (HEAD -> main) Initial commit: Add project structure
f9e8d7c Add README file

This is helpful for quickly getting an overview of recent changes.

Viewing Changes with --stat

If you want to see which files were changed in each commit and a summary of how many lines were added or removed, use the --stat option:

git log --stat

Output:

commit a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0 (HEAD -> main)
Author: Your Name <[email protected]>
Date:   Tue May 21 10:30:00 2024 +0000

    Initial commit: Add project structure

 src/app.js | 1 +
 src/style.css | 1 +
 2 files changed, 2 insertions(+)

commit f9e8d7c6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0
Author: Your Name <[email protected]>
Date:   Tue May 21 09:45:15 2024 +0000

    Add README file

 README.md | 5 +++++
 1 file changed, 5 insertions(+)

This shows the file paths relative to the project root, along with a simple visual representation (+ for additions, - for deletions) and a summary line.

Seeing the Actual Changes with --patch (-p)

To see the exact changes (the "diff" or "patch") introduced by each commit, use the -p or --patch option:

git log -p

Output (excerpt for one commit):

commit a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0 (HEAD -> main)
Author: Your Name <[email protected]>
Date:   Tue May 21 10:30:00 2024 +0000

    Initial commit: Add project structure

diff --git a/src/app.js b/src/app.js
new file mode 100644
index 0000000..e69de29
diff --git a/src/style.css b/src/style.css
new file mode 100644
index 0000000..e69de29

This output shows the differences in a format similar to the diff command. Lines starting with + were added, and lines starting with - were removed (though none were removed in this simple example of new files). This option is very detailed and useful for understanding specific changes but can produce a lot of output.

Limiting the Number of Commits

If you only want to see the last few commits, you can use the -n option, followed by the number of commits you want to view. For example, to see only the latest three commits:

git log -n 3

You can combine these options. For instance, to see a concise view of the last two commits with stats:

git log --oneline --stat -n 2

Output:

a1b2c3d (HEAD -> main) Initial commit: Add project structure
 src/app.js | 1 +
 src/style.css | 1 +
 2 files changed, 2 insertions(+)
f9e8d7c Add README file
 README.md | 5 +++++
 1 file changed, 5 insertions(+)

The git log command is your window into the history you are building with git commit. Experimenting with these options will help you navigate and understand your project's evolution effectively. As you progress, you'll find git log to be an indispensable tool for reviewing changes, finding when specific modifications were introduced, and understanding the work of collaborators.