~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/branches.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

    % bzr status

    A       src/

    ?       src/simple.c

    % bzr add src/simple.c

    % bzr status

    A       src/

    A       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

    ?       hello.txt

    D       src/

    D       src/simple.c

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 push plugin that comes with BzrTools