How to Use the Command 'git changelog' (with Examples)

The git changelog command is a part of the git-extras suite, designed to simplify the process of generating a changelog report from repository commits and tags. This tool is incredibly useful for developers looking to maintain clear records of a project’s progression by summarizing commit history in a structured format. By automating the generation of changelog content, it reduces manual overhead and ensures consistency in documenting software changes, updates, and releases.

Use case 1: Update existing file or create a new History.md file with the commit messages since the latest Git tag

Code:

git changelog

Motivation:

There are instances when developers want a simple and straightforward way to document the changes made since the last version of a project. Automatically generating or updating a History.md file ensures that all changes are captured and recorded, minimizing the potential for oversight. This is an effective practice for keeping a clear historical record of a project’s updates and changes for collaborators and end-users alike.

Explanation:

• The command git changelog without any additional options takes all the commits from the latest Git tag and compiles them into a changelog file. If History.md already exists, it appends the new changes to this file, otherwise, it creates a new one.

Example Output:

## v2.2.0 - 2023-09-30

- Fixed issue with data synchronization
- Improved logging for server diagnostics
- Added support for new payment gateway

Use case 2: List commits from the current version

Code:

git changelog --list

Motivation:

Understanding all changes made in the current version is crucial for developers, especially when preparing for a release or when documenting changes internally. Listing commits with detailed messages can serve as a checklist to ensure all features and fixes intended for a version have been implemented and merged correctly.

Explanation:

• The --list option transforms the changelog process into a listing operation, presenting commit messages on the terminal rather than updating or creating a file. This is useful for quickly reviewing changes without generating a persistent file.

Example Output:

* 237b43e: Updated README with new API routes
* 19fe953: Fixed bug causing crash on file upload
* a7d3e9f: Refactored database connection logic

Use case 3: List a range of commits from the tag named 2.1.0 to now

Code:

git changelog --list --start-tag 2.1.0

Motivation:

Project managers and developers often need to review specific ranges of changes, such as from a particular release to the current state of the project. This allows for focused analysis of progression and the opportunity to check whether all scheduled tasks for a milestone have been completed.

Explanation:

• --list lists the commits in the specified range.
• --start-tag 2.1.0 defines the beginning of the commit range from the tag 2.1.0.

Example Output:

* 04b1a92: Implemented feature Z for enhanced user experience
* 112a3de: Performance optimization for database queries
* 95b2c51: Removed deprecated API endpoint

Use case 4: List pretty formatted range of commits between the tag 0.5.0 and the tag 1.0.0

Code:

git changelog --start-tag 0.5.0 --final-tag 1.0.0

Motivation:

Generating a prettily formatted list of commits helps when preparing changelogs that require clarity and readability, such as documentation or reports for stakeholders. By creating a coherent summary between two specific milestones, developers can better communicate significant changes.

Explanation:

• --start-tag 0.5.0 signifies the initial point in the commit history from which changes should be listed.
• --final-tag 1.0.0 marks the endpoint for the changelog listing.

Example Output:

- Improved security protocol for user data handling
- Added localization support for multiple languages
- Updated third-party dependencies to latest versions

Use case 5: List pretty formatted range of commits between the commit 0b97430 and the tag 1.0.0

Code:

git changelog --start-commit 0b97430 --final-tag 1.0.0

Motivation:

Sometimes there is a need to track the development evolution from a specific commit hash to a particular version tag. This detailed visibility helps in debugging, auditing changes, or ensuring all requested features within that commit range are appropriately completed.

Explanation:

• --start-commit 0b97430 specifies the exact commit hash where the changelog process starts.
• --final-tag 1.0.0 establishes the endpoint using a tag.

Example Output:

- Implemented server-side validation for X form
- Improved accessibility features in user interface
- Documented API v2.0 endpoints and usage guidelines

Use case 6: Specify CHANGELOG.md as the output file

Code:

git changelog CHANGELOG.md

Motivation:

Different projects or organizations may have naming conventions for their documentation files. Specifying the output ensures consistency across project repositories and aligns with internal guidelines or conventions.

Explanation:

• CHANGELOG.md is explicitly defined as the file to create or update with changelog entries, leaving no ambiguity about where changes are recorded.

Example Output:

The file CHANGELOG.md is created or updated with the latest commit messages formatted appropriately for markdown presentation.

Use case 7: Replace contents of current changelog file entirely

Code:

git changelog --prune-old

Motivation:

During significant project revisions, starting fresh with a changelog may be necessary to reflect the new direction accurately or after major structural changes. Replacing the entire changelog content allows developers to discard outdated or irrelevant information, which can simplify the documentation.

Explanation:

• --prune-old tells git changelog to clear the contents of the existing changelog file before generating the new commits history, ensuring only the most recent commits are retained.

Example Output:

A completely revised file, devoid of previous changelog history, containing only current and desired commits.

Conclusion:

The git changelog command is a powerful asset for maintaining and viewing detailed commit histories across a software project. By exploring these use cases, developers can realize the versatility and efficiency brought by this command, strengthening documentation practices and simplifying the tracking of project development. Whether you need to update a changelog, review a specific range of commits, or reset your documentation, git changelog accommodates a vast array of needs in the lifecycle of a project.