/brz/remove-bazaar

.. 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-0.7pre, 2006-01-06.

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. (**Bazaar-NG 0.6 and later**). 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. (**Bazaar-NG 0.6 and later**) 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.  There is no repository or database as used in

svn or svk.

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

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 (Post Bazaar-NG 0.6) email setting in .

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 revision % 1000

    % 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.

Checkouts

=========

Another thing that gives you files to edit is a checkout. A checkout is

always associated with another branch. One of the purposes of checkouts is

to get multiple working trees for a branch. Another reason for checkouts is

to get access to the files in a branch without keeping a full copy of the

branch available locally. Getting a checkout looks like this::

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

    % cd bzr.dev

Checkouts have several advantages and drawbacks. A checkout does not have

any RCS history as the history is stored in the branch for which a checkout

is assocated with. This behaviour results in two general rules:

 1. checkouts take much less space than a full branch

 2. checkouts are much faster if the branch is on a local filesystem.

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 command only works if your local (destination) branch includes only

changes from the parent branch and no commits of its own.  Otherwise, the

branches are said to have ''diverged'', and they must be merged instead.

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

Conflicts during merge

======================

Sometimes two branches modify the same lines in the same files at the same

time. The result of this collision is called a "conflict". These conflicts

must be resolved by hand as Bazaar-NG can not tell which change you would

prefer to keep. You are, however, provided with some information which

makes the job easier for you to deal with.

The first thing that Bazaar-NG does is to merge in the parts that it can.

The parts that can not be merged are put into the file for you to decide

what to do with.

The second thing that Bazaar-NG does is to provide you with three extra

files for each file that is conflicted. The names of these files are the

same as the original filename with ".BASE", ".THIS" and ".OTHER" appended.

Each of these files serves a different purpose:

+------------------+-----------------------------------------------------+

| filename.BASE   | filename as it looked back when filename was         |

|                 | identical in both branches.                          |

+-----------------+------------------------------------------------------+

| filename.THIS   | The version of filename for this branch. All of the  |

|                 | parts of the merge with the other branch that can be |

|                 | merged from the other branch without conflicts are   |

|                 | accepted. The parts which conflict are thrown away   |

+-----------------+------------------------------------------------------+

| filename.OTHER  | The version of filename for the other branch. All of |

|                 | parts of the merge from this branch that can be      |

|                 | successfully merged are accepted. The parts of the   |

|                 | merge which conflict are thrown away                 |

+-----------------+------------------------------------------------------+

For example, imagine that you and another developer were working on on a

simple branch that only contained hello.c. Both of you agree that saying 

"Yo" to users is a little _too_ informal. Both of you also decide to fix

the problem at the same time, but take slightly different approaches. You

decide upon saying "Hi", while your compatriot decides upon a slightly more

formal "Hello". You both make the respective change and commit. Then, you

merge his change. The result would look something like this:

+----------------------+------------------------+

|  hello.c.THIS        |    hello.c.THAT        |

+----------------------+------------------------+

| | #include <stdio.h> | | #include <stdio.h>   |

| | int                | | int                  |

| | main()             | | main()               |

| | {                  | | {                    |

| |  printf("Hi");     | |   printf("Hello");   |

| | }                  | | }                    |

|                      |                        |

+----------------------+------------------------+

|    hello.c.BASE      |       hello.c          |

+----------------------+------------------------+

| | #include <stdio.h> | | #include <stdio.h>   |

| | int                | | int                  |

| | main()             | | main()               |

| | {                  | | {                    |

| |   printf("Yo");    | | <<<<<<< TREE         |

| | }                  | |   printf("Hi");      |

|                      | | =======              |

|                      | |   printf("Hello");   |

|                      | | <<<<<<< MERGE-SOURCE |

|                      | | }                    |

|                      |                        |

+----------------------+------------------------+

Your job as a developer is to decide which better. A multitude of options

exist for how to solve the conflict. Two of them are:

  1. Decide whether you'd like hello.c.THIS, hello.c.THAT or hello.c.BASE.

  Copy that one to hello.c.

  1. edit hello.c and decide which part you wish to keep. Your solution

  will be between the lines that say "<<<<<<< TREE" and "=======". His

  solution will be between "=======" and "<<<<<<< MERGE-SOURCE").  Do not

  forget to delete the markers too!

Bazaar also tracks which files conflicted during merge to prevent you from

accidentally committing the conflict markers to your branch. To tell

Bazaar-NG that you have fixed one of the conflicted files, run::

 % bzr resolve hello.c

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.

Publishing your branch

======================

You do not need a special server to publish a bzr branch. Generally

speaking, one can push a branch via sftp to a directory that is served via

apache. Bazaar-NG supports a variety of methods for reading and writing

branches.

Bazaar-NG can push branches via these methods::

  1. sftp via ssh (the most common)

  2. standard FTP

  3. Any filesystem mounted via remote filesystem tools like NFS and Samba

  4. The Canonical.com branch hosting service (via scoming soon)

  5. Rsync (requires bzrtools plugin from http://bazaar-vcs.org/BzrTools)

Bazaar-NG can also read branches via a variety of methods::

  1. Standard http, (E.g. Apache)

  2. rsync 

  3. FTP 

  3. SFTP

The most common approach is to push a branch via sftp to a place that is

served via SFTP. This usually looks something like::

 * You have a branch in ~/somebranch

 * You have a directory on /home/yourname/public_html on BigServer that

   shows up as http://BigServer/~yourname

In cases such as this, you'll usually perform the following commands to

initially push your branch via rsync (which requires the bzrtools plugin)::

 % cd somebranch/

 % bzr push yourname@BigServer:public_html/somebranch/

Other people can then access for your branch by doing the following::

 % cd anotherbranch/

 % bzr merge http://BigServer/~yourname/somebranch