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.. This file is in Python ReStructuredText format - it can be formatted
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.. into HTML or text. In the future we plan to extract the example commands
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.. and automatically test them.
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.. This text was previously on the wiki at
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.. http://bazaar.canonical.com/IntroductionToBzr but has been moved into the
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.. source tree so it can be kept in sync with
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.. the source and possibly automatically checked.
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Current for bzr-0.7pre, 2006-01-06.
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If you are already familiar with decentralized revision control, then
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please feel free to skip ahead to "Introducing Yourself to Bazaar-NG". If,
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on the other hand, you are familiar with revision control but not
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decentralized revision control, then please start at "How DRCS is
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different." Otherwise, get some coffee or tea, get comfortable and get
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The Purposes of Revision Control
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================================
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Odds are that you have worked on some sort of textual data -- the sources
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to a program, web sites or the config files that Unix system administrators
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have to deal with in /etc. The chances are also good that you have made
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some sort of mistake that you deeply regretted. Perhaps you deleted the
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configuration file for your mailserver or perhaps mauled the source code
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for a pet project. Whatever happened, you have just deleted important
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information that you would desperately like to get back. If this has ever
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happened to you, then you are probably ready for Bazaar-NG.
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Revision control systems (which I'll henceforth call RCS) such as Bazaar-NG
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give you the ability to track changes for a directory by turning it into
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something slightly more complicated than a directory that we call a
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**branch**. The branch not only stores how the directory looks right now,
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but also how it looked at various points in the past. Then, when you do
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something you wish you hadn't, you can restore the directory to the way it
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looked at some point in the past.
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Revision control systems give users the ability to save changes to a branch
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by "committing a **revision**". The revision created is essentially a
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summary of the changes that were made since the last time the tree was
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These revisions have other uses as well. For example, one can comment
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revisions to record what the recent set of changes meant by providing an
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optional log message. Real life log messages include things like "Fixed the
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web template to close the table" and "Added sftp suppport. Fixes #595"
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We keep these logs so that if later there is some sort of problem with
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sftp, we can figure out when the problem probably happened.
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Many Revision Control Systems (RCS) are stored on servers. If one wants to
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work on the code stored within an RCS, then one needs to connect to the
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server and "checkout" the code. Doing so gives one a directory in which a
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person can make changes and then commit. The RCS client then connects to
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the RCS server and stores the changes. This method is known as the
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The centralized model can have some drawbacks. A centralized RCS requires
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that one is able to connect to the server whenever one wants to do version
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control work. This can be a bit of a problem if your server on some other
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machine on the internet and you are not. Or, worse yet, you ''are'' on the
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internet but the server is missing!
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Decentralized Revision Control Systems (which I'll call DRCS after this
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point) deal with this problem by keeping branches on the same machine as
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the client. In Bazaar-NG's case, the branch is kept in the same place as
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the code that is being version controlled. This allows the user to save his
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changes (**commit**) whenever he wants -- even if he is offline. The user
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only needs internet access when he wants to access the changes in someone
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else's branch that are somewhere else.
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A common requirement that many people have is the need to keep track of the
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changes for a directory such as file and subdirectory changes. Performing
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this tracking by hand is a awkward process that over time becomes unwieldy.
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That is, until one considers version control tools such as Bazaar-NG. These
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tools automate the process of storing data by creating a **revision** of
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the directory tree whenever the user asks.
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Revision control software such as Bazaar-NG can do much more than just
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storage and performing undo. For example, with Bazaar-NG developer can
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take the modifications in one branch of software and apply them to another,
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related, branch -- even if those changes exist in a branch owned by
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somebody else. This allows developers to cooperate without giving write
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Bazaar-NG remembers the ''ancestry'' of a revision: the previous revisions
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that it is based upon. A single revision may have more than one direct
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descendant, each with different changes, representing a divergence in the
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evolution of the tree. By branching, Bazaar-NG allows multiple people to
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cooperate on the evolution of a project, without all needing to work in
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strict lock-step. Branching can be useful even for a single developer.
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Introducing yourself to Bazaar-NG
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=================================
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Bazaar-NG installs a single new command, **bzr**. Everything else is a
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subcommand of this. You can get some help with `bzr help`. There will be
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One function of a version control system is to keep track of who changed
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what. In a decentralized system, that requires an identifier for each
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author that is globally unique. Most people already have one of these: an
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email address. Bzr is smart enough to automatically generate an email
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address by looking up your username and hostname. If you don't like the
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guess that Bazaar-NG makes, then three options exist:
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1. (**Bazaar-NG 0.6 and later**). Setting the email address in the
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``~/.bazaar/bazaar.conf`` by adding the following lines. Please note that
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``[DEFAULT]`` is case sensitive::
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email= Your Name <email@isp.com>
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1. (**Bazaar-NG 0.6 and later**) Override the previous setting on a
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branch by branch basis by creating a branch section in
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``~/.bazaar/branches.conf`` by adding the following lines::
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[/the/directory/to/the/branch]
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email=Your Name <email@isp.com>
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1. Overriding the two previous options by setting the global environment
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variable ``$BZREMAIL`` or ``$EMAIL`` (``$BZREMAIL`` will take precedence)
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to your full email address.
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History is by default stored in the .bzr directory of the branch. There
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will be a facility to store it in a separate repository, which may be
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remote. We create a new branch by running **bzr init** in an existing
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/home/mbp/work/bzr.test/tutorial
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As for CVS, there are three classes of file: unknown, ignored, and
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versioned. The **add** command makes a file versioned: that is, changes to
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it will be recorded by the system::
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% echo 'hello world' > hello.txt
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If you add the wrong file, simply use **bzr remove** to make it unversioned
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again. This does not delete the working copy.
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All history is stored in a branch, which is just an on-disk directory
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containing control files. There is no repository or database as used in
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You'll usually refer to branches on your computer's filesystem just by
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giving the name of the directory containing the branch. bzr also supports
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accessing branches over http, for example::
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% bzr log http://bazaar-ng.org/bzr/bzr.dev/
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By installing bzr plugins you can also access branches over the sftp or
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Once you have completed some work, you will want to **commit** it to the
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version history. It is good to commit fairly often: whenever you get a new
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feature working, fix a bug, or improve some code or documentation. It's
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also a good practice to make sure that the code compiles and passes its
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test suite before committing, to make sure that every revision is a
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known-good state. You can also review your changes, to make sure you're
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committing what you intend to, and as a chance to rethink your work before
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you permanently record it.
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Two bzr commands are particularly useful here: **status** and **diff**.
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The **status** command tells you what changes have been made to the
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working directory since the last revision::
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By default **bzr status** hides "boring" files that are either unchanged or
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ignored. To see them too, use the --all option. The status command can
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optionally be given the name of some files or directories to check.
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The **diff** command shows the full text of changes to all files as a
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standard unified diff. This can be piped through many programs such as
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''patch'', ''diffstat'', ''filterdiff'' and ''colordiff''::
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*** added file 'hello.txt'
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With the ''-r'' option, the tree is compared to an earlier revision, or
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the differences between two versions are shown::
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% bzr diff -r 1000.. # everything since r1000
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% bzr diff -r 1000..1100 # changes from 1000 to 1100
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The --diff-options option causes bzr to run the external diff program,
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passing options. For example::
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% bzr diff --diff-options --side-by-side foo
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When the working tree state is satisfactory, it can be **committed** to the
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branch, creating a new revision holding a snapshot of that state.
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The **commit** command takes a message describing the changes in the
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revision. It also records your userid, the current time and timezone, and
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the inventory and contents of the tree. The commit message is specified by
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the ''-m'' or ''--message'' option. You can enter a multi-line commit
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message; in most shells you can enter this just by leaving the quotes open
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at the end of the line.
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% bzr commit -m "added my first file"
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You can also use the -F option to take the message from a file. Some
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people like to make notes for a commit message while they work, then review
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the diff to make sure they did what they said they did. (This file can
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also be useful when you pick up your work after a break.)
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Message from an editor
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======================
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If you use neither the `-m` nor the `-F` option then bzr will open an
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editor for you to enter a message. The editor to run is controlled by your
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`$EDITOR` environment variable or (Post Bazaar-NG 0.6) email setting in .
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If you quit the editor without making any changes, the commit will be
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If you give file or directory names on the commit command line then only
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the changes to those files will be committed. For example::
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% bzr commit -m "documentation fix" commit.py
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By default bzr always commits all changes to the tree, even if run from a
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subdirectory. To commit from only the current directory down, use::
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Removing uncommitted changes
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============================
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If you've made some changes and don't want to keep them, use the **revert**
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command to go back to the previous head version. It's a good idea to use
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**bzr diff** first to see what will be removed. By default the revert
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command reverts the whole tree; if file or directory names are given then
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only those ones will be affected. **revert** also clears the list of
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pending merges revisions.
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Many source trees contain some files that do not need to be versioned, such
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as editor backups, object or bytecode files, and built programs. You can
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simply not add them, but then they'll always crop up as unknown files. You
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can also tell bzr to ignore these files by adding them to a file called
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''.bzrignore'' at the top of the tree.
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This file contains a list of file wildcards (or "globs"), one per line.
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Typical contents are like this::
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If a glob contains a slash, it is matched against the whole path from the
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top of the tree; otherwise it is matched against only the filename. So
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the previous example ignores files with extension ``.o`` in all
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subdirectories, but this example ignores only config.h at the top level
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and HTML files in ``doc/``::
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To get a list of which files are ignored and what pattern they matched, use
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It is OK to have either an ignore pattern match a versioned file, or to add
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an ignored file. Ignore patterns have no effect on versioned files; they
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only determine whether unversioned files are reported as unknown or
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The ''.bzrignore'' file should normally be versioned, so that new copies of
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the branch see the same patterns::
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% bzr commit -m "Add ignore patterns"
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The **bzr log** command shows a list of previous revisions. The **bzr log
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--forward** command does the same in chronological order to get most recent
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revisions printed at last.
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As with bzr diff, bzr log supports the -r argument::
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% bzr log -r 1000.. # Revision 1000 and everything after it
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% bzr log -r ..1000 # Everything up to and including revision % 1000
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% bzr log -r 1000..1100 # changes from 1000 to 1100
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% bzr log -r 1000 # The changes in only revision 1000
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The **bzr info** command shows some summary information about the working
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tree and the branch history.
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Versioning directories
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======================
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bzr versions files and directories in a way that can keep track of renames
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and intelligently merge them::
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% echo 'int main() {}' > src/simple.c
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% bzr add src/simple.c
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Deleting and removing files
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===========================
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You can delete files or directories by just deleting them from the working
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directory. This is a bit different to CVS, which requires that you also do
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**bzr remove** makes the file un-versioned, but does not delete the working
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copy. This is useful when you add the wrong file, or decide that a file
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should actually not be versioned.
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% bzr remove -v hello.txt
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If you remove the wrong file by accident, you can use **bzr revert** to restore it.
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Often rather than starting your own project, you will want to submit a
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change to an existing project. You can get a copy of an existing branch by
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copying its directory, expanding a tarball, or by a remote copy using
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something like rsync. You can also use bzr to fetch a copy. Because this
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new copy is potentially a new branch, the command is called *branch*::
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% bzr branch http://bazaar-ng.org/bzr/bzr.dev
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This copies down the complete history of this branch, so we can do all
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operations on it locally: log, annotate, making and merging branches.
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There will be an option to get only part of the history if you wish.
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Another thing that gives you files to edit is a checkout. A checkout is
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always associated with another branch. One of the purposes of checkouts is
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to get multiple working trees for a branch. Another reason for checkouts is
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to get access to the files in a branch without keeping a full copy of the
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branch available locally. Getting a checkout looks like this::
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% bzr checkout http://bazaar-ng.org/bzr/bzr.dev
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Checkouts have several advantages and drawbacks. A checkout does not have
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any RCS history as the history is stored in the branch for which a checkout
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is assocated with. This behaviour results in two general rules:
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1. checkouts take much less space than a full branch
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2. checkouts are much faster if the branch is on a local filesystem.
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Following upstream changes
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==========================
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You can stay up-to-date with the parent branch by "pulling" in their changes
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After this change, the local directory will be a mirror of the source.
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This command only works if your local (destination) branch includes only
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changes from the parent branch and no commits of its own. Otherwise, the
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branches are said to have ''diverged'', and they must be merged instead.
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Merging from related branches
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=============================
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If two branches have diverged (both have unique changes) then **bzr merge**
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is the appropriate command to use. Merge will automatically calculate the
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changes that exist in the branch you're merging from that are not in your
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branch and attempt to apply them in your branch. ::
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Conflicts during merge
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======================
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Sometimes two branches modify the same lines in the same files at the same
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time. The result of this collision is called a "conflict". These conflicts
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must be resolved by hand as Bazaar-NG can not tell which change you would
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prefer to keep. You are, however, provided with some information which
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makes the job easier for you to deal with.
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The first thing that Bazaar-NG does is to merge in the parts that it can.
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The parts that can not be merged are put into the file for you to decide
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The second thing that Bazaar-NG does is to provide you with three extra
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files for each file that is conflicted. The names of these files are the
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same as the original filename with ".BASE", ".THIS" and ".OTHER" appended.
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Each of these files serves a different purpose:
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+------------------+-----------------------------------------------------+
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| filename.BASE | filename as it looked back when filename was |
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| | identical in both branches. |
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+-----------------+------------------------------------------------------+
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| filename.THIS | The version of filename for this branch. All of the |
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| | parts of the merge with the other branch that can be |
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| | merged from the other branch without conflicts are |
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| | accepted. The parts which conflict are thrown away |
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+-----------------+------------------------------------------------------+
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| filename.OTHER | The version of filename for the other branch. All of |
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| | parts of the merge from this branch that can be |
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| | successfully merged are accepted. The parts of the |
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| | merge which conflict are thrown away |
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+-----------------+------------------------------------------------------+
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For example, imagine that you and another developer were working on on a
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simple branch that only contained hello.c. Both of you agree that saying
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"Yo" to users is a little _too_ informal. Both of you also decide to fix
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the problem at the same time, but take slightly different approaches. You
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decide upon saying "Hi", while your compatriot decides upon a slightly more
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formal "Hello". You both make the respective change and commit. Then, you
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merge his change. The result would look something like this:
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+----------------------+------------------------+
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| hello.c.THIS | hello.c.THAT |
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+----------------------+------------------------+
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| | #include <stdio.h> | | #include <stdio.h> |
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| | main() | | main() |
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| | printf("Hi"); | | printf("Hello"); |
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+----------------------+------------------------+
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| hello.c.BASE | hello.c |
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+----------------------+------------------------+
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| | #include <stdio.h> | | #include <stdio.h> |
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| | main() | | main() |
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| | printf("Yo"); | | <<<<<<< TREE |
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| | } | | printf("Hi"); |
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| | | printf("Hello"); |
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| | | <<<<<<< MERGE-SOURCE |
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+----------------------+------------------------+
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Your job as a developer is to decide which better. A multitude of options
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exist for how to solve the conflict. Two of them are:
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1. Decide whether you'd like hello.c.THIS, hello.c.THAT or hello.c.BASE.
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Copy that one to hello.c.
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1. edit hello.c and decide which part you wish to keep. Your solution
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will be between the lines that say "<<<<<<< TREE" and "=======". His
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solution will be between "=======" and "<<<<<<< MERGE-SOURCE"). Do not
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forget to delete the markers too!
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Bazaar also tracks which files conflicted during merge to prevent you from
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accidentally committing the conflict markers to your branch. To tell
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Bazaar-NG that you have fixed one of the conflicted files, run::
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% bzr resolve hello.c
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Using a program such as kdiff3, you can now comfortably merge them into one
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file. To commit you have to rename it to the original basename and delete
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the other two files. As long as there exist files with .BASE, .THIS or
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.OTHER the commit command will complain.
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Publishing your branch
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======================
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You do not need a special server to publish a bzr branch. Generally
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speaking, one can push a branch via sftp to a directory that is served via
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apache. Bazaar-NG supports a variety of methods for reading and writing
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Bazaar-NG can push branches via these methods::
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1. sftp via ssh (the most common)
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3. Any filesystem mounted via remote filesystem tools like NFS and Samba
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4. The Canonical.com branch hosting service (via scoming soon)
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5. Rsync (requires bzrtools plugin from http://bazaar-vcs.org/BzrTools)
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Bazaar-NG can also read branches via a variety of methods::
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1. Standard http, (E.g. Apache)
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The most common approach is to push a branch via sftp to a place that is
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served via SFTP. This usually looks something like::
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* You have a branch in ~/somebranch
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* You have a directory on /home/yourname/public_html on BigServer that
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shows up as http://BigServer/~yourname
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In cases such as this, you'll usually perform the following commands to
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initially push your branch via rsync (which requires the bzrtools plugin)::
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% bzr push yourname@BigServer:public_html/somebranch/
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Other people can then access for your branch by doing the following::
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% bzr merge http://BigServer/~yourname/somebranch
added
removed
doc/tutorial.txt
