~bzr-pqm/bzr/bzr.dev

.. This file is in Python ReStructuredText format - it can be formatted
.. into HTML or text.  In the future we plan to extract the example commands
.. and automatically test them.

.. This text was previously on the wiki at 
.. http://bazaar.canonical.com/IntroductionToBzr
.. but has been moved into the source tree so it can be kept in sync with
.. the source and possibly automatically checked.

==================
Bazaar-NG Tutorial
==================

Current for bzr-0.8, 2006-04


Introduction
============

If you are already familiar with decentralized revision control, then
please feel free to skip ahead to "Introducing Yourself to Bazaar-NG". If,
on the other hand, you are familiar with revision control but not
decentralized revision control, then please start at "How DRCS is
different." Otherwise, get some coffee or tea, get comfortable and get
ready to catch up. 

The Purposes of Revision Control
================================

Odds are that you have worked on some sort of textual data -- the sources
to a program, web sites or the config files that Unix system
administrators have to deal with in /etc. The chances are also good that
you have made some sort of mistake that you deeply regretted. Perhaps you
deleted the configuration file for your mailserver or perhaps mauled the
source code for a pet project. Whatever happened, you have just deleted
important information that you would desperately like to get back. If this
has ever happened to you, then you are probably ready for Bazaar-NG.

Revision control systems (which I'll henceforth call RCS) such as
Bazaar-NG give you the ability to track changes for a directory by turning
it into something slightly more complicated than a directory that we call
a **branch**. The branch not only stores how the directory looks right
now, but also how it looked at various points in the past. Then, when you
do something you wish you hadn't, you can restore the directory to the way
it looked at some point in the past.

Revision control systems give users the ability to save changes to a
branch by "committing a **revision**". The revision created is essentially
a summary of the changes that were made since the last time the tree was
saved. 

These revisions have other uses as well. For example, one can comment
revisions to record what the recent set of changes meant by providing an
optional log message. Real life log messages include things like "Fixed
the web template to close the table" and "Added sftp suppport. Fixes #595"
	
We keep these logs so that if later there is some sort of problem with
sftp, we can figure out when the problem probably happened. 

How DRCS is Different
---------------------

Many Revision Control Systems (RCS) are stored on servers. If one wants to
work on the code stored within an RCS, then one needs to connect to the
server and "checkout" the code. Doing so gives one a directory in which a
person can make changes and then commit. The RCS client then connects to
the RCS server and stores the changes. This method is known as the
centralized model. 

The centralized model can have some drawbacks. A centralized RCS requires
that one is able to connect to the server whenever one wants to do version
control work. This can be a bit of a problem if your server on some other
machine on the internet and you are not. Or, worse yet, you ''are'' on the
internet but the server is missing!

Decentralized Revision Control Systems (which I'll call DRCS after this
point) deal with this problem by keeping branches on the same machine as
the client. In Bazaar-NG's case, the branch is kept in the same place as
the code that is being version controlled. This allows the user to save
his changes (**commit**) whenever he wants -- even if he is offline. The
user only needs internet access when he wants to access the changes in
someone else's branch that are somewhere else.

 
A common requirement that many people have is the need to keep track of
the changes for a directory such as file and subdirectory changes.
Performing this tracking by hand is a awkward process that over time
becomes unwieldy. That is, until one considers version control tools such
as Bazaar-NG. These tools automate the process of storing data by creating
a **revision** of the directory tree whenever the user asks. 

Revision control software such as Bazaar-NG can do much more than just
storage and performing undo.  For example, with Bazaar-NG developer can
take the modifications in one branch of software and apply them to
another, related, branch -- even if those changes exist in a branch owned
by somebody else. This allows developers to cooperate without giving write
access to repository.

Bazaar-NG remembers the ''ancestry'' of a revision: the previous revisions
that it is based upon.  A single revision may have more than one direct
descendant, each with different changes, representing a divergence in the
evolution of the tree. By branching, Bazaar-NG allows multiple people to
cooperate on the evolution of a project, without all needing to work in
strict lock-step.  Branching can be useful even for a single developer.

Introducing yourself to Bazaar-NG
=================================

Bazaar-NG installs a single new command, **bzr**.  Everything else is a
subcommand of this.  You can get some help with `bzr help`.  There will be
more in the future.

One function of a version control system is to keep track of who changed
what.  In a decentralized system, that requires an identifier for each
author that is globally unique.  Most people already have one of these: an
email address. Bzr is smart enough to automatically generate an email
address by looking up your username and hostname. If you don't like the
guess that Bazaar-NG makes, then three options exist:

 1. Setting the email address in the
 ``~/.bazaar/bazaar.conf`` by adding the following lines. Please note that
 ``[DEFAULT]`` is case sensitive::

    [DEFAULT]
    email= Your Name <email@isp.com>
 
 1. Override the previous setting on a
 branch by branch basis by creating a branch section in
 ``~/.bazaar/locations.conf`` by adding the following lines::

    [/the/directory/to/the/branch]
    email=Your Name <email@isp.com>
 
 1. Overriding the two previous options by setting the global environment
 variable ``$BZREMAIL`` or ``$EMAIL`` (``$BZREMAIL`` will take precedence) 
 to your full email address.

Creating a branch
=================

History is by default stored in the .bzr directory of the branch. There
will be a facility to store it in a separate repository, which may be
remote.  We create a new branch by running **bzr init** in an existing
directory::

    % mkdir tutorial
    % cd tutorial
    % ls -a
    ./  ../
    % pwd
    /home/mbp/work/bzr.test/tutorial
    %
    % bzr init
    % ls -aF
    ./  ../  .bzr/
    %

As for CVS, there are three classes of file: unknown, ignored, and
versioned.  The **add** command makes a file versioned: that is, changes
to it will be recorded by the system::

    % echo 'hello world' > hello.txt
    % bzr status
    unknown:
      hello.txt
    % bzr unknowns
    hello.txt
    % bzr add hello.txt
    added hello.txt
    % bzr unknowns


If you add the wrong file, simply use **bzr remove** to make it
unversioned again.  This does not delete the working copy.

Branch locations
================

All history is stored in a branch, which is just an on-disk directory
containing control files.  By default there is no separate repository or
database as used in svn or svk. You can choose to create a repository if
you want to (see the **bzr init-repo** command). You may wish to do this
if you have very large branches, or many branches of a moderate sized
project.

You'll usually refer to branches on your computer's filesystem just by
giving the name of the directory containing the branch.  bzr also supports
accessing branches over http, for example::

    % bzr log http://bazaar-ng.org/bzr/bzr.dev/

By installing bzr plugins you can also access branches over the sftp or
rsync protocols.

Reviewing changes
=================

Once you have completed some work, you will want to **commit** it to the
version history.  It is good to commit fairly often: whenever you get a
new feature working, fix a bug, or improve some code or documentation.
It's also a good practice to make sure that the code compiles and passes
its test suite before committing, to make sure that every revision is a
known-good state.  You can also review your changes, to make sure you're
committing what you intend to, and as a chance to rethink your work before
you permanently record it. 

Two bzr commands are particularly useful here: **status** and **diff**.  

bzr status
----------

The **status** command tells you what changes have been made to the
working directory since the last revision::

    % bzr status
    modified:
       foo

By default **bzr status** hides "boring" files that are either unchanged
or ignored.  To see them too, use the --all option.  The status command
can optionally be given the name of some files or directories to check.

bzr diff
--------

The **diff** command shows the full text of changes to all files as a
standard unified diff.  This can be piped through many programs such as
''patch'', ''diffstat'', ''filterdiff'' and ''colordiff''::

    % bzr diff
    *** added file 'hello.txt'
    --- /dev/null 
    +++ hello.txt 
    @@ -1,0 +1,1 @@
    +hello world


With the ''-r'' option, the tree is compared to an earlier revision, or
the differences between two versions are shown::

    % bzr diff -r 1000..          # everything since r1000
    % bzr diff -r 1000..1100      # changes from 1000 to 1100

The --diff-options option causes bzr to run the external diff program,
passing options.  For example::

    % bzr diff --diff-options --side-by-side foo

Some projects prefer patches to show a prefix at the start of the path for
old and new files.  The --prefix option can be used to provide such a prefix. 
As a shortcut, ``bzr diff -p1`` produces a form that works with the 
command ``patch -p1``.

Committing changes
==================

When the working tree state is satisfactory, it can be **committed** to
the branch, creating a new revision holding a snapshot of that state.  

bzr commit
----------

The **commit** command takes a message describing the changes in the
revision.  It also records your userid, the current time and timezone, and
the inventory and contents of the tree.  The commit message is specified
by the ''-m'' or ''--message'' option. You can enter a multi-line commit
message; in most shells you can enter this just by leaving the quotes open
at the end of the line.

::

    % bzr commit -m "added my first file"

You can also use the -F option to take the message from a file.  Some
people like to make notes for a commit message while they work, then
review the diff to make sure they did what they said they did.  (This file
can also be useful when you pick up your work after a break.)

Message from an editor
======================

If you use neither the `-m` nor the `-F` option then bzr will open an
editor for you to enter a message.  The editor to run is controlled by
your `$EDITOR` environment variable or 
add `editor` to ~/.bazaar/bazaar.conf; `$BZR_EDITOR` will override
the above mentioned editor options.  If you quit the editor without
making any changes, the commit will be cancelled.

Selective commit
----------------

If you give file or directory names on the commit command line then only
the changes to those files will be committed.  For example::

    % bzr commit -m "documentation fix" commit.py

By default bzr always commits all changes to the tree, even if run from a
subdirectory.  To commit from only the current directory down, use::

    % bzr commit .


Removing uncommitted changes
============================

If you've made some changes and don't want to keep them, use the
**revert** command to go back to the previous head version.  It's a good
idea to use **bzr diff** first to see what will be removed. By default the
revert command reverts the whole tree; if file or directory names are
given then only those ones will be affected. **revert** also clears the
list of pending merges revisions.

Ignoring files
==============

Many source trees contain some files that do not need to be versioned,
such as editor backups, object or bytecode files, and built programs.  You
can simply not add them, but then they'll always crop up as unknown files.
You can also tell bzr to ignore these files by adding them to a file
called ''.bzrignore'' at the top of the tree.

This file contains a list of file wildcards (or "globs"), one per line.
Typical contents are like this::

    *.o
    *~
    *.tmp
    *.py[co]

If a glob contains a slash, it is matched against the whole path from the
top of the tree; otherwise it is matched against only the filename.  So
the previous example ignores files with extension ``.o`` in all
subdirectories, but this example ignores only config.h at the top level
and HTML files in ``doc/``::

    ./config.h
    doc/*.html

To get a list of which files are ignored and what pattern they matched,
use ''bzr ignored''::

    % bzr ignored
    config.h                 ./config.h
    configure.in~            *~

It is OK to have either an ignore pattern match a versioned file, or to
add an ignored file.  Ignore patterns have no effect on versioned files;
they only determine whether unversioned files are reported as unknown or
ignored.

The ''.bzrignore'' file should normally be versioned, so that new copies
of the branch see the same patterns::

    % bzr add .bzrignore
    % bzr commit -m "Add ignore patterns"


Examining history
=================

bzr log
-------

The **bzr log** command shows a list of previous revisions. The **bzr log
--forward** command does the same in chronological order to get most
recent revisions printed at last.

As with bzr diff, bzr log supports the -r argument::

    % bzr log -r 1000..          # Revision 1000 and everything after it
    % bzr log -r ..1000          # Everything up to and including r1000
    % bzr log -r 1000..1100      # changes from 1000 to 1100
    % bzr log -r 1000            # The changes in only revision 1000


Branch statistics
=================

The **bzr info** command shows some summary information about the working
tree and the branch history.  


Versioning directories
======================

bzr versions files and directories in a way that can keep track of renames
and intelligently merge them::

    % mkdir src
    % echo 'int main() {}' > src/simple.c
    % bzr add src
    added src
    added src/simple.c
    % bzr status
    added:
      src/
      src/simple.c


Deleting and removing files
===========================

You can delete files or directories by just deleting them from the working
directory.  This is a bit different to CVS, which requires that you also
do **cvs remove**.

    **bzr remove** makes the file un-versioned, but does not delete
    the working copy.  This is useful when you add the wrong file, or decide
    that a file should actually not be versioned. 

::

    % rm -r src
    % bzr remove -v hello.txt
    ?       hello.txt
    % bzr status
    removed:
      hello.txt
      src/
      src/simple.c
    unknown:
      hello.txt

If you remove the wrong file by accident, you can use **bzr revert** to
restore it.


Branching
=========

Often rather than starting your own project, you will want to submit a
change to an existing project.  You can get a copy of an existing branch
by copying its directory, expanding a tarball, or by a remote copy using
something like rsync.  You can also use bzr to fetch a copy.  Because this
new copy is potentially a new branch, the command is called *branch*::

    % bzr branch http://bazaar-ng.org/bzr/bzr.dev 
    % cd bzr.dev

This copies down the complete history of this branch, so we can do all
operations on it locally: log, annotate, making and merging branches.
There will be an option to get only part of the history if you wish.

Following upstream changes
==========================

You can stay up-to-date with the parent branch by "pulling" in their
changes::

    % bzr pull

After this change, the local directory will be a mirror of the source. This
includes the ''revision-history'' - which is a list of the commits done in 
this branch, rather than merged from other branches.

This command only works if your local (destination) branch is either an
older copy of the parent branch with no new commits of its own, or if the
most recent commit in your local branch has been merged into the parent
branch.

Merging from related branches
=============================

If two branches have diverged (both have unique changes) then **bzr
merge** is the appropriate command to use. Merge will automatically
calculate the changes that exist in the branch you're merging from that
are not in your branch and attempt to apply them in your branch.

::

  % bzr merge URL


If there is a conflict during a merge, 3 files with the same basename are
created. The filename of the common base is appended with .BASE, the
filename of the file containing your changes is appended .THIS and the
filename with the changes from the other tree is appended .OTHER.
Using a program such as kdiff3, you can now comfortably merge them into
one file. To commit you have to rename it to the original basename and
delete the other two files. As long as there exist files with .BASE, .THIS
or .OTHER the commit command will complain.

[**TODO**: explain conflict markers within files]


Publishing your branch
======================

You don't need a special server to publish a bzr branch, just a normal web
server.  Just mirror the files to your server, including the .bzr
directory.  One can push a branch (or the changes for a branch) by one of
the following three methods:

* Rsync:   rsync -avrz LOCALBRANCH  servername.com/this/directory/here

  (or any other tool for publishing a directory to a web site.)

* bzr push sftp://servername.com/this/directory/here 

  (The directory that must already exist)

* The rspush plugin that comes with BzrTools