
bos@95: \chapter{A tour of Mercurial: the basics}
bos@95: \label{chap:tour-basic}
bos@84: 
bos@84: \section{Installing Mercurial on your system}
bos@84: \label{sec:tour:install}
bos@84: 
bos@85: Prebuilt binary packages of Mercurial are available for every popular
bos@85: operating system.  These make it easy to start using Mercurial on your
bos@85: computer immediately.
bos@85: 
bos@84: \subsection{Linux}
bos@84: 
bos@84: Because each Linux distribution has its own packaging tools, policies,
bos@84: and rate of development, it's difficult to give a comprehensive set of
bos@85: instructions on how to install Mercurial binaries.  The version of
bos@85: Mercurial that you will end up with can vary depending on how active
bos@85: the person is who maintains the package for your distribution.
bos@84: 
bos@84: To keep things simple, I will focus on installing Mercurial from the
bos@84: command line under the most popular Linux distributions.  Most of
bos@84: these distributions provide graphical package managers that will let
bos@84: you install Mercurial with a single click; the package name to look
bos@84: for is \texttt{mercurial}.
bos@84: 
bos@85: \begin{itemize}
bos@85: \item[Debian]
bos@85:   \begin{codesample4}
bos@85:     apt-get install mercurial
bos@85:   \end{codesample4}
bos@84: 
bos@85: \item[Fedora Core]
bos@85:   \begin{codesample4}
bos@85:     yum install mercurial
bos@85:   \end{codesample4}
bos@84: 
bos@85: \item[Gentoo]
bos@85:   \begin{codesample4}
bos@85:     emerge mercurial
bos@85:   \end{codesample4}
bos@84: 
bos@85: \item[OpenSUSE]
bos@85:   \begin{codesample4}
bos@85:     yum install mercurial
bos@85:   \end{codesample4}
bos@84: 
bos@262: \item[Ubuntu] Ubuntu's Mercurial package is based on Debian's.  To
bos@262:   install it, run the following command.
bos@262:   \begin{codesample4}
bos@262:     apt-get install mercurial
bos@262:   \end{codesample4}
bos@262:   The Ubuntu package for Mercurial tends to lag behind the Debian
bos@262:   version by a considerable time margin (at the time of writing, seven
bos@262:   months), which in some cases will mean that on Ubuntu, you may run
bos@262:   into problems that have since been fixed in the Debian package.
bos@85: \end{itemize}
bos@84: 
bos@84: \subsection{Mac OS X}
bos@84: 
bos@84: Lee Cantey publishes an installer of Mercurial for Mac OS~X at
bos@84: \url{http://mercurial.berkwood.com}.  This package works on both
bos@85: Intel-~and Power-based Macs.  Before you can use it, you must install
bos@85: a compatible version of Universal MacPython~\cite{web:macpython}.  This
bos@85: is easy to do; simply follow the instructions on Lee's site.
bos@84: 
bos@84: \subsection{Solaris}
bos@84: 
bos@84: XXX.
bos@84: 
bos@84: \subsection{Windows}
bos@84: 
bos@84: Lee Cantey publishes an installer of Mercurial for Windows at
bos@84: \url{http://mercurial.berkwood.com}.  This package has no external
bos@84: dependencies; it ``just works''.
bos@84: 
bos@84: \begin{note}
bos@84:   The Windows version of Mercurial does not automatically convert line
bos@84:   endings between Windows and Unix styles.  If you want to share work
bos@84:   with Unix users, you must do a little additional configuration
bos@84:   work. XXX Flesh this out.
bos@84: \end{note}
bos@84: 
bos@87: \section{Getting started}
bos@87: 
bos@87: To begin, we'll use the \hgcmd{version} command to find out whether
bos@87: Mercurial is actually installed properly.  The actual version
bos@87: information that it prints isn't so important; it's whether it prints
bos@87: anything at all that we care about.
bos@87: \interaction{tour.version}
bos@87: 
bos@87: \subsection{Built-in help}
bos@87: 
steve@158: Mercurial provides a built-in help system.  This is invaluable for those
bos@87: times when you find yourself stuck trying to remember how to run a
bos@87: command.  If you are completely stuck, simply run \hgcmd{help}; it
bos@87: will print a brief list of commands, along with a description of what
bos@87: each does.  If you ask for help on a specific command (as below), it
bos@87: prints more detailed information.
bos@87: \interaction{tour.help}
bos@87: For a more impressive level of detail (which you won't usually need)
bos@87: run \hgcmdargs{help}{\hggopt{-v}}.  The \hggopt{-v} option is short
bos@87: for \hggopt{--verbose}, and tells Mercurial to print more information
bos@87: than it usually would.
bos@87: 
bos@87: \section{Working with a repository}
bos@87: 
bos@87: In Mercurial, everything happens inside a \emph{repository}.  The
bos@87: repository for a project contains all of the files that ``belong to''
bos@87: that project, along with a historical record of the project's files.
bos@87: 
bos@87: There's nothing particularly magical about a repository; it is simply
bos@87: a directory tree in your filesystem that Mercurial treats as special.
steve@158: You can rename or delete a repository any time you like, using either the
bos@87: command line or your file browser.
bos@87: 
bos@88: \subsection{Making a local copy of a repository}
bos@87: 
bos@87: \emph{Copying} a repository is just a little bit special.  While you
bos@87: could use a normal file copying command to make a copy of a
bos@87: repository, it's best to use a built-in command that Mercurial
bos@87: provides.  This command is called \hgcmd{clone}, because it creates an
bos@87: identical copy of an existing repository.
bos@87: \interaction{tour.clone}
bos@87: If our clone succeeded, we should now have a local directory called
bos@87: \dirname{hello}.  This directory will contain some files.
bos@87: \interaction{tour.ls}
bos@87: These files have the same contents and history in our repository as
bos@87: they do in the repository we cloned.
bos@87: 
bos@87: Every Mercurial repository is complete, self-contained, and
bos@87: independent.  It contains its own private copy of a project's files
bos@87: and history.  A cloned repository remembers the location of the
bos@87: repository it was cloned from, but it does not communicate with that
bos@87: repository, or any other, unless you tell it to.
bos@87: 
bos@87: What this means for now is that we're free to experiment with our
bos@87: repository, safe in the knowledge that it's a private ``sandbox'' that
bos@87: won't affect anyone else.
bos@85: 
bos@88: \subsection{What's in a repository?}
bos@88: 
bos@88: When we take a more detailed look inside a repository, we can see that
bos@88: it contains a directory named \dirname{.hg}.  This is where Mercurial
bos@88: keeps all of its metadata for the repository.
bos@88: \interaction{tour.ls-a}
bos@88: 
bos@88: The contents of the \dirname{.hg} directory and its subdirectories are
bos@88: private to Mercurial.  Every other file and directory in the
bos@88: repository is yours to do with as you please.
bos@88: 
bos@88: To introduce a little terminology, the \dirname{.hg} directory is the
bos@88: ``real'' repository, and all of the files and directories that coexist
bos@91: with it are said to live in the \emph{working directory}.  An easy way
bos@91: to remember the distinction is that the \emph{repository} contains the
bos@88: \emph{history} of your project, while the \emph{working directory}
bos@88: contains a \emph{snapshot} of your project at a particular point in
bos@88: history.
bos@88: 
bos@88: \section{A tour through history}
bos@88: 
bos@88: One of the first things we might want to do with a new, unfamiliar
bos@88: repository is understand its history.  The \hgcmd{log} command gives
bos@88: us a view of history.
bos@88: \interaction{tour.log}
bos@88: By default, this command prints a brief paragraph of output for each
bos@88: change to the project that was recorded.  In Mercurial terminology, we
bos@88: call each of these recorded events a \emph{changeset}, because it can
bos@88: contain a record of changes to several files.
bos@88: 
bos@88: The fields in a record of output from \hgcmd{log} are as follows.
bos@88: \begin{itemize}
bos@88: \item[\texttt{changeset}] This field has the format of a number,
bos@88:   followed by a colon, followed by a hexadecimal string.  These are
bos@88:   \emph{identifiers} for the changeset.  There are two identifiers
bos@88:   because the number is shorter and easier to type than the hex
bos@88:   string.
bos@88: \item[\texttt{user}] The identity of the person who created the
bos@88:   changeset.  This is a free-form field, but it most often contains a
bos@88:   person's name and email address.
bos@88: \item[\texttt{date}] The date and time on which the changeset was
steve@158:   created, and the timezone in which it was created.  (The date and
bos@88:   time are local to that timezone; they display what time and date it
bos@88:   was for the person who created the changeset.)
bos@88: \item[\texttt{summary}] The first line of the text message that the
bos@88:   creator of the changeset entered to describe the changeset.
bos@88: \end{itemize}
bos@88: The default output printed by \hgcmd{log} is purely a summary; it is
bos@88: missing a lot of detail.
bos@88: 
bos@99: Figure~\ref{fig:tour-basic:history} provides a graphical representation of
bos@97: the history of the \dirname{hello} repository, to make it a little
bos@97: easier to see which direction history is ``flowing'' in.  We'll be
bos@97: returning to this figure several times in this chapter and the chapter
bos@97: that follows.
bos@97: 
bos@96: \begin{figure}[ht]
bos@96:   \centering
bos@96:   \grafix{tour-history}
bos@96:   \caption{Graphical history of the \dirname{hello} repository}
bos@99:   \label{fig:tour-basic:history}
bos@96: \end{figure}
bos@96: 
bos@97: \subsection{Changesets, revisions, and talking to other 
bos@97:   people}
bos@97: 
bos@97: As English is a notoriously sloppy language, and computer science has
bos@99: a hallowed history of terminological confusion (why use one term when
bos@99: four will do?), revision control has a variety of words and phrases
bos@99: that mean the same thing.  If you are talking about Mercurial history
bos@99: with other people, you will find that the word ``changeset'' is often
bos@99: compressed to ``change'' or (when written) ``cset'', and sometimes a
bos@99: changeset is referred to as a ``revision'' or a ``rev''.
bos@88: 
bos@88: While it doesn't matter what \emph{word} you use to refer to the
bos@88: concept of ``a~changeset'', the \emph{identifier} that you use to
bos@88: refer to ``a~\emph{specific} changeset'' is of great importance.
bos@88: Recall that the \texttt{changeset} field in the output from
bos@88: \hgcmd{log} identifies a changeset using both a number and a
bos@97: hexadecimal string.
bos@97: \begin{itemize}
bos@97: \item The revision number is \emph{only valid in that repository},
bos@97: \item while the hex string is the \emph{permanent, unchanging
bos@97:     identifier} that will always identify that exact changeset in
bos@97:   \emph{every} copy of the repository.
bos@97: \end{itemize}
bos@88: This distinction is important.  If you send someone an email talking
bos@88: about ``revision~33'', there's a high likelihood that their
bos@88: revision~33 will \emph{not be the same} as yours.  The reason for this
bos@88: is that a revision number depends on the order in which changes
bos@88: arrived in a repository, and there is no guarantee that the same
bos@88: changes will happen in the same order in different repositories.
bos@88: Three changes $a,b,c$ can easily appear in one repository as $0,1,2$,
bos@88: while in another as $1,0,2$.
bos@88: 
bos@88: Mercurial uses revision numbers purely as a convenient shorthand.  If
bos@88: you need to discuss a changeset with someone, or make a record of a
bos@88: changeset for some other reason (for example, in a bug report), use
bos@88: the hexadecimal identifier.
bos@88: 
bos@88: \subsection{Viewing specific revisions}
bos@88: 
bos@88: To narrow the output of \hgcmd{log} down to a single revision, use the
bos@91: \hgopt{log}{-r} (or \hgopt{log}{--rev}) option.  You can use either a
bos@91: revision number or a long-form changeset identifier, and you can
bos@91: provide as many revisions as you want.  \interaction{tour.log-r}
bos@88: 
bos@88: If you want to see the history of several revisions without having to
bos@88: list each one, you can use \emph{range notation}; this lets you
bos@88: express the idea ``I want all revisions between $a$ and $b$,
bos@88: inclusive''.
bos@88: \interaction{tour.log.range}
bos@88: Mercurial also honours the order in which you specify revisions, so
bos@88: \hgcmdargs{log}{-r 2:4} prints $2,3,4$ while \hgcmdargs{log}{-r 4:2}
bos@88: prints $4,3,2$.
bos@88: 
bos@91: \subsection{More detailed information}
bos@91: 
bos@91: While the summary information printed by \hgcmd{log} is useful if you
bos@91: already know what you're looking for, you may need to see a complete
bos@91: description of the change, or a list of the files changed, if you're
bos@91: trying to decide whether a changeset is the one you're looking for.
bos@91: The \hgcmd{log} command's \hggopt{-v} (or \hggopt{--verbose})
bos@91: option gives you this extra detail.
bos@91: \interaction{tour.log-v}
bos@91: 
bos@91: If you want to see both the description and content of a change, add
bos@91: the \hgopt{log}{-p} (or \hgopt{log}{--patch}) option.  This displays
bos@91: the content of a change as a \emph{unified diff} (if you've never seen
bos@91: a unified diff before, see section~\ref{sec:mq:patch} for an overview).
bos@91: \interaction{tour.log-vp}
bos@91: 
bos@91: \section{All about command options}
bos@91: 
bos@91: Let's take a brief break from exploring Mercurial commands to discuss
bos@91: a pattern in the way that they work; you may find this useful to keep
steve@158: in mind as we continue our tour.
bos@91: 
bos@91: Mercurial has a consistent and straightforward approach to dealing
bos@91: with the options that you can pass to commands.  It follows the
bos@91: conventions for options that are common to modern Linux and Unix
bos@91: systems.
bos@91: \begin{itemize}
bos@91: \item Every option has a long name.  For example, as we've already
bos@91:   seen, the \hgcmd{log} command accepts a \hgopt{log}{--rev} option.
bos@91: \item Most options have short names, too.  Instead of
bos@91:   \hgopt{log}{--rev}, we can use \hgopt{log}{-r}.  (The reason that
bos@91:   some options don't have short names is that the options in question
bos@91:   are rarely used.)
bos@91: \item Long options start with two dashes (e.g.~\hgopt{log}{--rev}),
bos@91:   while short options start with one (e.g.~\hgopt{log}{-r}).
bos@91: \item Option naming and usage is consistent across commands.  For
bos@91:   example, every command that lets you specify a changeset~ID or
bos@91:   revision number accepts both \hgopt{log}{-r} and \hgopt{log}{--rev}
bos@91:   arguments.
bos@91: \end{itemize}
bos@91: In the examples throughout this book, I use short options instead of
bos@91: long.  This just reflects my own preference, so don't read anything
bos@91: significant into it.
bos@91: 
bos@91: Most commands that print output of some kind will print more output
bos@91: when passed a \hggopt{-v} (or \hggopt{--verbose}) option, and less
bos@91: when passed \hggopt{-q} (or \hggopt{--quiet}).
bos@91: 
bos@91: \section{Making and reviewing changes}
bos@91: 
bos@91: Now that we have a grasp of viewing history in Mercurial, let's take a
bos@91: look at making some changes and examining them.
bos@91: 
bos@91: The first thing we'll do is isolate our experiment in a repository of
bos@91: its own.  We use the \hgcmd{clone} command, but we don't need to
bos@91: clone a copy of the remote repository.  Since we already have a copy
bos@91: of it locally, we can just clone that instead.  This is much faster
bos@91: than cloning over the network, and cloning a local repository uses
bos@91: less disk space in most cases, too.
bos@91: \interaction{tour.reclone}
bos@91: As an aside, it's often good practice to keep a ``pristine'' copy of a
bos@91: remote repository around, which you can then make temporary clones of
bos@91: to create sandboxes for each task you want to work on.  This lets you
bos@91: work on multiple tasks in parallel, each isolated from the others
bos@91: until it's complete and you're ready to integrate it back.  Because
bos@91: local clones are so cheap, there's almost no overhead to cloning and
bos@91: destroying repositories whenever you want.
bos@91: 
bos@91: In our \dirname{my-hello} repository, we have a file
bos@91: \filename{hello.c} that contains the classic ``hello, world'' program.
bos@91: Let's use the ancient and venerable \command{sed} command to edit this
bos@91: file so that it prints a second line of output.  (I'm only using
bos@91: \command{sed} to do this because it's easy to write a scripted example
bos@91: this way.  Since you're not under the same constraint, you probably
bos@91: won't want to use \command{sed}; simply use your preferred text editor to
bos@91: do the same thing.)
bos@91: \interaction{tour.sed}
bos@91: 
bos@91: Mercurial's \hgcmd{status} command will tell us what Mercurial knows
bos@91: about the files in the repository.
bos@91: \interaction{tour.status}
bos@91: The \hgcmd{status} command prints no output for some files, but a line
bos@91: starting with ``\texttt{M}'' for \filename{hello.c}.  Unless you tell
bos@91: it to, \hgcmd{status} will not print any output for files that have
bos@91: not been modified.  
bos@91: 
bos@91: The ``\texttt{M}'' indicates that Mercurial has noticed that we
bos@97: modified \filename{hello.c}.  We didn't need to \emph{inform}
bos@97: Mercurial that we were going to modify the file before we started, or
bos@97: that we had modified the file after we were done; it was able to
bos@97: figure this out itself.
bos@91: 
bos@91: It's a little bit helpful to know that we've modified
bos@91: \filename{hello.c}, but we might prefer to know exactly \emph{what}
bos@91: changes we've made to it.  To do this, we use the \hgcmd{diff}
bos@91: command.
bos@91: \interaction{tour.diff}
bos@91: 
bos@91: \section{Recording changes in a new changeset}
bos@91: 
bos@91: We can modify files, build and test our changes, and use
bos@91: \hgcmd{status} and \hgcmd{diff} to review our changes, until we're
bos@91: satisfied with what we've done and arrive at a natural stopping point
bos@91: where we want to record our work in a new changeset.
bos@91: 
bos@91: The \hgcmd{commit} command lets us create a new changeset; we'll
bos@91: usually refer to this as ``making a commit'' or ``committing''.  
bos@91: 
bos@102: \subsection{Setting up a username}
bos@102: 
bos@174: When you try to run \hgcmd{commit} for the first time, it is not
bos@174: guaranteed to succeed.  Mercurial records your name and address with
bos@174: each change that you commit, so that you and others will later be able
bos@174: to tell who made each change.  Mercurial tries to automatically figure
bos@174: out a sensible username to commit the change with.  It will attempt
bos@174: each of the following methods, in order:
bos@174: \begin{enumerate}
bos@174: \item If you specify a \hgopt{commit}{-u} option to the \hgcmd{commit}
bos@174:   command on the command line, followed by a username, this is always
bos@174:   given the highest precedence.
bos@174: \item If you have set the \envar{HGUSER} environment variable, this is
bos@174:   checked next.
bos@174: \item If you create a file in your home directory called
bos@174:   \sfilename{.hgrc}, with a \rcitem{ui}{username} entry, that will be
bos@174:   used next.  To see what the contents of this file should look like,
bos@174:   refer to section~\ref{sec:tour-basic:username} below.
bos@174: \item If you have set the \envar{EMAIL} environment variable, this
bos@174:   will be used next.
bos@174: \item Mercurial will query your system to find out your local user
bos@174:   name and host name, and construct a username from these components.
bos@174:   Since this often results in a username that is not very useful, it
bos@174:   will print a warning if it has to do this.
bos@174: \end{enumerate}
bos@174: If all of these mechanisms fail, Mercurial will fail, printing an
bos@174: error message.  In this case, it will not let you commit until you set
bos@174: up a username.
bos@174: 
bos@174: You should think of the \envar{HGUSER} environment variable and the
bos@174: \hgopt{commit}{-u} option to the \hgcmd{commit} command as ways to
bos@174: \emph{override} Mercurial's default selection of username.  For normal
bos@174: use, the simplest and most robust way to set a username for yourself
bos@174: is by creating a \sfilename{.hgrc} file; see below for details.
bos@102: 
bos@102: \subsubsection{Creating a Mercurial configuration file}
bos@174: \label{sec:tour-basic:username}
bos@102: 
bos@102: To set a user name, use your favourite editor to create a file called
bos@102: \sfilename{.hgrc} in your home directory.  Mercurial will use this
bos@102: file to look up your personalised configuration settings.  The initial
bos@102: contents of your \sfilename{.hgrc} should look like this.
bos@102: \begin{codesample2}
bos@102:   # This is a Mercurial configuration file.
bos@102:   [ui]
bos@102:   username = Firstname Lastname <email.address@domain.net>
bos@102: \end{codesample2}
bos@102: The ``\texttt{[ui]}'' line begins a \emph{section} of the config file,
bos@102: so you can read the ``\texttt{username = ...}'' line as meaning ``set
bos@102: the value of the \texttt{username} item in the \texttt{ui} section''.
bos@102: A section continues until a new section begins, or the end of the
bos@102: file.  Mercurial ignores empty lines and treats any text from
bos@102: ``\texttt{\#}'' to the end of a line as a comment.
bos@102: 
bos@102: \subsubsection{Choosing a user name}
bos@102: 
bos@102: You can use any text you like as the value of the \texttt{username}
bos@102: config item, since this information is for reading by other people,
bos@102: but for interpreting by Mercurial.  The convention that most people
bos@102: follow is to use their name and email address, as in the example
bos@102: above.
bos@102: 
bos@102: \begin{note}
bos@102:   Mercurial's built-in web server obfuscates email addresses, to make
bos@102:   it more difficult for the email harvesting tools that spammers use.
bos@102:   This reduces the likelihood that you'll start receiving more junk
bos@102:   email if you publish a Mercurial repository on the web.
bos@102: \end{note}
bos@102: 
bos@91: \subsection{Writing a commit message}
bos@91: 
bos@91: When we commit a change, Mercurial drops us into a text editor, to
bos@91: enter a message that will describe the modifications we've made in
bos@91: this changeset.  This is called the \emph{commit message}.  It will be
bos@91: a record for readers of what we did and why, and it will be printed by
bos@91: \hgcmd{log} after we've finished committing.
bos@91: \interaction{tour.commit}
bos@91: 
bos@91: The editor that the \hgcmd{commit} command drops us into will contain
bos@91: an empty line, followed by a number of lines starting with
bos@91: ``\texttt{HG:}''.
bos@91: \begin{codesample2}
bos@91:   \emph{empty line}
bos@91:   HG: changed hello.c
bos@91: \end{codesample2}
bos@91: Mercurial ignores the lines that start with ``\texttt{HG:}''; it uses
bos@91: them only to tell us which files it's recording changes to.  Modifying
bos@91: or deleting these lines has no effect.
bos@91: 
bos@91: \subsection{Writing a good commit message}
bos@91: 
bos@91: Since \hgcmd{log} only prints the first line of a commit message by
bos@91: default, it's best to write a commit message whose first line stands
bos@91: alone.  Here's a real example of a commit message that \emph{doesn't}
bos@91: follow this guideline, and hence has a summary that is not readable.
bos@91: \begin{codesample2}
bos@91:   changeset:   73:584af0e231be
bos@91:   user:        Censored Person <censored.person@example.org>
bos@91:   date:        Tue Sep 26 21:37:07 2006 -0700
bos@91:   summary:     include buildmeister/commondefs.   Add an exports and install
bos@91: \end{codesample2}
bos@91: 
bos@91: As far as the remainder of the contents of the commit message are
bos@91: concerned, there are no hard-and-fast rules.  Mercurial itself doesn't
bos@91: interpret or care about the contents of the commit message, though
bos@91: your project may have policies that dictate a certain kind of
bos@91: formatting.
bos@91: 
bos@91: My personal preference is for short, but informative, commit messages
bos@91: that tell me something that I can't figure out with a quick glance at
bos@91: the output of \hgcmdargs{log}{--patch}.
bos@91: 
bos@91: \subsection{Aborting a commit}
bos@91: 
bos@91: If you decide that you don't want to commit while in the middle of
bos@91: editing a commit message, simply exit from your editor without saving
bos@91: the file that it's editing.  This will cause nothing to happen to
bos@91: either the repository or the working directory.
bos@91: 
bos@91: If we run the \hgcmd{commit} command without any arguments, it records
bos@91: all of the changes we've made, as reported by \hgcmd{status} and
bos@91: \hgcmd{diff}.
bos@91: 
bos@102: \subsection{Admiring our new handiwork}
bos@91: 
bos@91: Once we've finished the commit, we can use the \hgcmd{tip} command to
bos@91: display the changeset we just created.  This command produces output
bos@91: that is identical to \hgcmd{log}, but it only displays the newest
bos@91: revision in the repository.
bos@91: \interaction{tour.tip}
bos@91: We refer to the newest revision in the repository as the tip revision,
bos@91: or simply the tip.
bos@91: 
bos@91: \section{Sharing changes}
bos@91: 
bos@91: We mentioned earlier that repositories in Mercurial are
bos@91: self-contained.  This means that the changeset we just created exists
bos@91: only in our \dirname{my-hello} repository.  Let's look at a few ways
bos@91: that we can propagate this change into other repositories.
bos@91: 
bos@91: \subsection{Pulling changes from another repository}
bos@91: \label{sec:tour:pull}
bos@91: 
bos@91: To get started, let's clone our original \dirname{hello} repository,
bos@91: which does not contain the change we just committed.  We'll call our
bos@91: temporary repository \dirname{hello-pull}.
bos@91: \interaction{tour.clone-pull}
bos@91: 
bos@91: We'll use the \hgcmd{pull} command to bring changes from
bos@91: \dirname{my-hello} into \dirname{hello-pull}.  However, blindly
bos@91: pulling unknown changes into a repository is a somewhat scary
bos@91: prospect.  Mercurial provides the \hgcmd{incoming} command to tell us
bos@91: what changes the \hgcmd{pull} command \emph{would} pull into the
bos@91: repository, without actually pulling the changes in.
bos@91: \interaction{tour.incoming}
bos@91: (Of course, someone could cause more changesets to appear in the
bos@91: repository that we ran \hgcmd{incoming} in, before we get a chance to
bos@91: \hgcmd{pull} the changes, so that we could end up pulling changes that we
bos@91: didn't expect.)
bos@91: 
bos@91: Bringing changes into a repository is a simple matter of running the
bos@91: \hgcmd{pull} command, and telling it which repository to pull from.
bos@91: \interaction{tour.pull}
bos@91: As you can see from the before-and-after output of \hgcmd{tip}, we
bos@91: have successfully pulled changes into our repository.  There remains
bos@92: one step before we can see these changes in the working directory.
bos@92: 
bos@92: \subsection{Updating the working directory}
bos@92: 
bos@92: We have so far glossed over the relationship between a repository and
bos@91: its working directory.  The \hgcmd{pull} command that we ran in
bos@91: section~\ref{sec:tour:pull} brought changes into the repository, but
bos@91: if we check, there's no sign of those changes in the working
bos@91: directory.  This is because \hgcmd{pull} does not (by default) touch
bos@91: the working directory.  Instead, we use the \hgcmd{update} command to
bos@91: do this.
bos@91: \interaction{tour.update}
bos@91: 
bos@91: It might seem a bit strange that \hgcmd{pull} doesn't update the
bos@91: working directory automatically.  There's actually a good reason for
bos@91: this: you can use \hgcmd{update} to update the working directory to
bos@91: the state it was in at \emph{any revision} in the history of the
bos@91: repository.  If you had the working directory updated to an old
bos@91: revision---to hunt down the origin of a bug, say---and ran a
bos@91: \hgcmd{pull} which automatically updated the working directory to a
bos@91: new revision, you might not be terribly happy.
bos@91: 
bos@91: However, since pull-then-update is such a common thing to do,
bos@91: Mercurial lets you combine the two by passing the \hgopt{pull}{-u}
bos@91: option to \hgcmd{pull}.
bos@91: \begin{codesample2}
bos@91:   hg pull -u
bos@91: \end{codesample2}
bos@92: If you look back at the output of \hgcmd{pull} in
bos@92: section~\ref{sec:tour:pull} when we ran it without \hgopt{pull}{-u},
bos@92: you can see that it printed a helpful reminder that we'd have to take
bos@92: an explicit step to update the working directory:
bos@92: \begin{codesample2}
bos@92:   (run 'hg update' to get a working copy)
bos@92: \end{codesample2}
bos@91: 
bos@91: To find out what revision the working directory is at, use the
bos@91: \hgcmd{parents} command.
bos@91: \interaction{tour.parents}
bos@101: If you look back at figure~\ref{fig:tour-basic:history}, you'll see
bos@101: arrows connecting each changeset.  The node that the arrow leads
bos@101: \emph{from} in each case is a parent, and the node that the arrow
bos@101: leads \emph{to} is its child.  The working directory has a parent in
bos@101: just the same way; this is the changeset that the working directory
bos@101: currently contains.
bos@101: 
bos@91: To update the working directory to a particular revision, give a
bos@91: revision number or changeset~ID to the \hgcmd{update} command.
bos@91: \interaction{tour.older}
bos@91: If you omit an explicit revision, \hgcmd{update} will update to the
bos@94: tip revision, as shown by the second call to \hgcmd{update} in the
bos@94: example above.
bos@91: 
bos@92: \subsection{Pushing changes to another repository}
bos@92: 
bos@92: Mercurial lets us push changes to another repository, from the
bos@92: repository we're currently visiting.  As with the example of
bos@92: \hgcmd{pull} above, we'll create a temporary repository to push our
bos@92: changes into.
bos@92: \interaction{tour.clone-push}
bos@92: The \hgcmd{outgoing} command tells us what changes would be pushed
bos@92: into another repository.
bos@92: \interaction{tour.outgoing}
bos@92: And the \hgcmd{push} command does the actual push.
bos@92: \interaction{tour.push}
bos@92: As with \hgcmd{pull}, the \hgcmd{push} command does not update the
bos@92: working directory in the repository that it's pushing changes into.
bos@92: (Unlike \hgcmd{pull}, \hgcmd{push} does not provide a \texttt{-u}
bos@92: option that updates the other repository's working directory.)
bos@92: 
bos@92: What happens if we try to pull or push changes and the receiving
bos@92: repository already has those changes?  Nothing too exciting.
bos@92: \interaction{tour.push.nothing}
bos@92: 
bos@93: \subsection{Sharing changes over a network}
bos@93: 
bos@93: The commands we have covered in the previous few sections are not
bos@93: limited to working with local repositories.  Each works in exactly the
bos@93: same fashion over a network connection; simply pass in a URL instead
bos@93: of a local path.
bos@93: \interaction{tour.outgoing.net}
bos@93: In this example, we can see what changes we could push to the remote
bos@93: repository, but the repository is understandably not set up to let
bos@93: anonymous users push to it.
bos@93: \interaction{tour.push.net}
bos@93: 
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