What is Bazaar?

Bazaar is a tool for helping people collaborate. It tracks the changes that you and other people make to a group of files - such as software source code - to give you snapshots of each stage of their evolution. Using that information, Bazaar can effortlessly merge your work with other people’s.

Tools like Bazaar are called version control systems (VCS) and have long been popular with software developers. Bazaar’s ease of use, flexibility and simple setup make it ideal not only for software developers but also for other groups who work together on files and documents, such as technical writers, web designers and translators.

This guide takes you through installing Bazaar and how to use it, whether on your own or with a team of other people. If you’re already familiar with distributed version control and want to dive straight in, you may wish to skim this section and jump straight to Learning more.

A brief history of version control systems

Version control tools have been evolving for several decades now. In simple terms, there have been 4 generations of tools:

1. file versioning tools, e.g. SCCS, RCS
2. tree versioning tools - central style, e.g. CVS
3. tree versioning tools - central style, take two, e.g. Subversion
4. tree versioning tools - distributed style, e.g. Bazaar.

The design and implementation of Bazaar builds on the lessons learned from all the previous generations of tools. In particular, Bazaar cleanly supports both the central and the distributed version control models so you can change models as it makes sense, without needing to change tools.

Central vs distributed VCS

Many traditional VCS tools require a central server which provides the change history or repository for a tree of files. To work on the files, users need to connect to the server and checkout the files. This gives them a directory or working tree in which a person can make changes. To record or commit these changes, the user needs access to the central server and they need to ensure they have merged their work with the latest version stored before trying to commit. This approach is known as the centralized model.

The centralized model has proven useful over time but it can have some notable drawbacks. Firstly, a centralized VCS requires that one is able to connect to the server whenever one wants to do version control work. Secondly, the centralized model tightly links the act of snapshotting changes with the act of publishing those changes. This can be good in some circumstances but it has a negative influence on quality in others.

Distributed VCS tools let users and teams have multiple repositories rather than just a single central one. In Bazaar’s case, the history is normally kept in the same place as the code that is being version controlled. This allows the user to commit their changes whenever it makes sense, even when offline. Network access is only required when publishing changes or when accessing changes in another location.

In fact, using distributed VCS tools wisely can have advantages well beyond the obvious one of disconnected operations for developers. Other advantages include:

• easier for developers to create experimental branches
• easier ad-hoc collaboration with peers
• less time required on mechanical tasks - more time for creativity
• increased release management flexibility through the use of “feature-wide” commits
• trunk quality and stability can be kept higher, making everyone’s job less stressful
• in open source communities:
  • easier for non-core developers to create and maintain changes
  • easier for core developers to work with non-core developers and move them into the core
• in companies, easier to work with distributed and outsourced teams.

For a detailed look at the advantages of distributed VCS tools over centralized VCS tools, see http://bazaar-vcs.org/BzrWhy.

Key features of Bazaar

While Bazaar is not the only distributed VCS tool around, it does have some notable features that make it an excellent choice for many teams and communities. A summary of these and comparisons with other VCS tools can be found on the Bazaar Wiki, http://bazaar-vcs.org.

Of the many features, one in particular is worth highlighting: Bazaar is completely free software written in Python. As a result, it is easy to contribute improvements. If you wish to get involved, please see http://bazaar-vcs.org/BzrSupport.

Learning more

This manual provides an easy to read introduction to Bazaar and how to use it effectively. It is recommended that all users read at least the rest of this chapter as it:

• explains the core concepts users need to know
• introduces some popular ways of using Bazaar to collaborate.

Chapters 2-6 provide a closer look at how to use Bazaar to complete various tasks. It is recommended that most users read these in first-to-last order shortly after starting to use Bazaar. Chapter 7 and beyond provide additional information that helps you make the most of Bazaar once the core functionality is understood. This material can be read when required and in any order.

If you are already familiar with other version control tools, you may wish to get started quickly by reading the following documents:

• Bazaar in five minutes - a mini-tutorial
• Bazaar Quick Start Card - a one page summary of commonly used commands.

In addition, the online help and Bazaar User Reference provide all the details on the commands and options available.

We hope you find this manual useful. If you have suggestions on how it or the rest of Bazaar’s documentation can be improved, please contact us on the mailing list, bazaar@lists.canonical.com.