~bzr-pqm/bzr/bzr.dev

1185.1.29 by Robert Collins
merge merge tweaks from aaron, which includes latest .dev
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Learn Bazaar in twenty minutes
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:Author:
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  Martin Pool <mbp@sourcefrog.net>
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:Date: November 2004, London
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*Bazaar* is an open source distributed version control system.  A
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version control system helps you develop software (or other documents)
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In Bazaar, branches hold a history of their changes.  All working
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copies are branches, and all branches are working copies.
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Let's get a copy of someone else's published project::
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    $ baz branch http://baz.alice.org/hello-2.6
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This creates a directory called ``hello-2.6`` in your current
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directory, containing Alice's *Hello World* 2.6 tree and a history of
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her changes.  We'll leave this directory containing a pristine copy of
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her work for future reference.
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We want to add a new feature.  Branching and merging is are cheap and
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easy in Baz, so development of each new feature should be done on a
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new branch -- this lets you merge them in different orders, and leave
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aside new development to fix a bug if you want.  It's good to choose a
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meaningful name for your development branches so that you can keep
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them straight.  So let's make an additional branch, based off our
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local copy of Alice's branch::
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    $ baz branch ./hello-2.6 ./hello-2.6-goodbye
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This command completed quickly: we didn't need to fetch anything from
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Alice's server to make a new branch.
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Now we have a second directory containing another copy of the source,
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with a different name.  Of course both are still the same as Alice's
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source.  Time to hack::
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    $ cd hello-2.6-goodbye
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    $ vi hello.c
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We add a new and much-desired ``--goodbye`` option, build and test
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it.  Having got to a good state, we think we're ready to commit our
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changes.  Many people find it helpful to review the changes before
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committing them, just to make sure there were no accidental mistakes::
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    $ baz diff | less
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This shows the changes relative to the version we started with.  If
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that looks OK, we're ready to commit::
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    $ baz commit -m 'Add --goodbye option'
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This records the changes into this branch.  We can see that they got
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recorded::
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    $ baz log | less
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This will show our change as the most recent, preceded by all our
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development.  If we only want to see our own changes, we can filter
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the log in various ways::
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    $ baz log --author bruce@ 
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    $ baz log --date today 
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(That second one might include anything Alice did before we started.)
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Since our changes were committed, we don't have anything outstanding,
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as we can see with this command::
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    $ baz diff 
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    No changes
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Thinking about it a bit more, we decide that it's too messy to mix the
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"Goodbye" implementation in with "Hello world".  We start up our
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editor and split it our into a new separate file, ``bye.c``.  By
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default, Baz assumes unknown files in the working directory are
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scratch files -- the same behaviour as CVS and Subversion.  We need to
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tell Baz that this file should be versioned, and then we can commit::
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    $ baz add bye.c
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    $ baz commit -s 'Refactor bye() into separate file'
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Of course this commits all our changes as a single atomic
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transaction.  If we wanted, we could tell Baz to build the program
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before committing to help ensure we never get a broken build.
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We're ready to publish our improved Hello World, but first we want to
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make sure we've integrated anything Alice has done while we were
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working.  First we update our mirror of Alice's branch::
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    $ baz sync ../hello-2.6
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This pulls the history of her branch onto our machine; we could
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disconnect from the network at this point and do all the merging work
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without needing to connect to ``alice.org``.   
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Now we'll pull Alice's new changes into our branch.  We can use a
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mirror of her branch, or we can go straight to her public branch.  In
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fact, we can merge from different copies of the same branch at
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different times, and Baz will still understand which changesets have
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already been merged.  Either of these commands will work::
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    $ baz merge ../hello-2.6
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    $ baz merge http://baz.alice.org/hello-2.6
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This pulls down any changesets on Alice's branch that aren't in ours,
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and applies them to our tree.  Since we've made changes in parallel
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with Alice, those changes might conflict.  Baz by default will insert
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CVS-style conflict markers into your branch if that happens, but you
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can also ask it to run a graphical merge tool or to tell emacs to do
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the merge.  Baz will help you merge changes other than file text, such
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as a file being renamed in one branch.  
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By running ``baz diff`` we can see the effect of her changes on our
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tree.  By running ``baz log --pending`` we can see a description of
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all of the changes that were pulled in.  Once the changes have been
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reconciled (which will often happen automatically), we can commit this
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to our branch::
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    $ baz commit -s 'Merge from Alice'
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Baz records that our change incorporates those patches from Alice::
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    $ baz log | less
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Now that we have the feature we wanted, we can publish our branch on
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the web.  We could copy it up using ``baz branch``, but because Baz
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branches are simply directories we can just rsync it onto a web
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server, even if the web server doesn't have Baz installed::
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    $ rsync -av ./hello-2.6-goodbye webserver.com:public_html/
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We send an email to Alice asking her to merge from this location.
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Typically she'll want to have a look at those changes before accepting
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them, and she can do that by running ``merge`` then ``diff``, as we
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did before.  If she likes the change, she can merge it, possibly
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applying some fixes in the process.  Next time we merge from her,
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we'll see our changes are in.
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.. Local variables:
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.. mode: rst
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.. compile-command: "rest2html short-demo.txt > short-demo.html"
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.. End:
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