Why Should You Look at Git Logs?¶

When using Git for version control, the commit history serves as the “growth record” of a project. By examining the logs, you can understand:
- Who made which changes and when;
- The project’s iteration trajectory (feature additions, bug fixes, refactoring, etc.);
- Quickly identify which commit introduced a specific issue.

The Most Basic git log Command¶

The simplest command to view logs is git log, which displays all commit records by default, ordered with the latest commit first.

Example output (simplified):

commit a1b2c3d4e5f67890 (HEAD -> master)
Author: Xiaoming <xiaoming@example.com>
Date:   Fri Oct 20 14:30:00 2023 +0800
    Fixed the issue where the user login button was unclickable

commit 9876543210fedcba
Author: Xiaohong <xiaohong@example.com>
Date:   Thu Oct 19 10:15:00 2023 +0800
    Added the user registration page

• commit: Unique ID for each commit (a string of characters used to identify the commit);
• Author: Committer and email;
• Date: Commit time;
• Commit message: Description of the changes (extremely important! Be clear).

Common git log Parameters (to Make Logs Clearer)¶

The default git log output is verbose. Using parameters allows filtering or simplifying logs for different scenarios.

1. Simplified Display: --oneline¶

To quickly browse the commit history, use --oneline to compress each commit into a single line, showing only the commit ID and a brief message:

git log --oneline

Example output:

a1b2c3d Fixed the user login button unclickable issue
9876543 Added user registration page
4567890 Initialized project structure

2. View Code Changes: -p (or --patch)¶

To see exactly which code changes a commit introduced, use -p to display the code diff for each commit:

git log -p

The output will show details like diff --git a/file.txt b/file.txt after the commit message, highlighting added/deleted lines (red for deletions, green for additions).

Pro Tip: Press q to exit the log view.

3. Limit Number of Commits: -n (or --max-count)¶

If there are too many commits, and you only want to see the last 5, use -n 5 to limit the number of displayed commits:

git log -n 3  # Shows the last 3 commits

4. Graphical Branch Structure: --graph¶

When the project has multiple merged branches, use --graph to visualize branch and merge relationships with ASCII characters:

git log --graph --oneline

Example output:

* a1b2c3d Fixed login button issue
|\
| * e4f5g6h Added payment feature
|/
* 9876543 Optimized homepage loading speed

Here, * represents a commit, and |// represent branch structures.

5. Filter by Author/Time: --author/--since/--before¶

• By author: git log --author="Xiaoming" shows only Xiaoming’s commits;
• By time: git log --since="2023-10-01" shows commits after October 1, 2023; --before="2023-10-01" shows commits before that date.

6. Colored Output: --color¶

For better readability, use --color to color-code commits (enabled by default; add --color=always to ensure color output):

git log --color --oneline

How to Analyze Commit History?¶

After learning to view logs, focus on extracting insights:

1. Identify the source of an issue:
   If a feature suddenly breaks, run git log --oneline to review recent commits, then use git log -p to compare differences between commits and pinpoint the problematic commit.

2. Understand branch logic:
   Use --graph with branch names (e.g., git log --graph --oneline --all) to visualize which commits belong to which branches and whether merges occurred.

3. Value of commit messages:
   Well-written commit messages (e.g., “Fixed login button issue” instead of “Modified code”) greatly improve log readability, facilitating team collaboration and future maintenance.

Summary: Essential Parameters for Beginners¶

With these commands, you can easily view, filter, and analyze Git commit history for more efficient version control. Remember: Clear commit records are the “golden key” for team collaboration and personal project maintenance!