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1 \chapter{A tour of Mercurial: the basics}
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2 \label{chap:tour-basic}
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3
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4 \section{Installing Mercurial on your system}
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5 \label{sec:tour:install}
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6
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7 Prebuilt binary packages of Mercurial are available for every popular
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8 operating system. These make it easy to start using Mercurial on your
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9 computer immediately.
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10
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11 \subsection{Linux}
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12
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13 Because each Linux distribution has its own packaging tools, policies,
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14 and rate of development, it's difficult to give a comprehensive set of
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15 instructions on how to install Mercurial binaries. The version of
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16 Mercurial that you will end up with can vary depending on how active
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17 the person is who maintains the package for your distribution.
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18
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19 To keep things simple, I will focus on installing Mercurial from the
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20 command line under the most popular Linux distributions. Most of
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21 these distributions provide graphical package managers that will let
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22 you install Mercurial with a single click; the package name to look
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23 for is \texttt{mercurial}.
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24
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25 \begin{itemize}
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26 \item[Debian]
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27 \begin{codesample4}
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28 apt-get install mercurial
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29 \end{codesample4}
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30
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31 \item[Fedora Core]
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32 \begin{codesample4}
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33 yum install mercurial
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34 \end{codesample4}
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35
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36 \item[Gentoo]
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37 \begin{codesample4}
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38 emerge mercurial
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39 \end{codesample4}
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40
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41 \item[OpenSUSE]
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42 \begin{codesample4}
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43 yum install mercurial
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44 \end{codesample4}
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45
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46 \item[Ubuntu] Ubuntu's Mercurial package is particularly old, and you
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47 should not use it. If you know how, you can rebuild and install the
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48 Debian package. It's probably easier to build Mercurial from source
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49 and simply run that; see section~\ref{sec:srcinstall:unixlike} for
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50 details.
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51 \end{itemize}
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52
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53 \subsection{Mac OS X}
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54
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55 Lee Cantey publishes an installer of Mercurial for Mac OS~X at
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56 \url{http://mercurial.berkwood.com}. This package works on both
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57 Intel-~and Power-based Macs. Before you can use it, you must install
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58 a compatible version of Universal MacPython~\cite{web:macpython}. This
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59 is easy to do; simply follow the instructions on Lee's site.
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60
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61 \subsection{Solaris}
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62
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63 XXX.
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64
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65 \subsection{Windows}
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66
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67 Lee Cantey publishes an installer of Mercurial for Windows at
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68 \url{http://mercurial.berkwood.com}. This package has no external
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69 dependencies; it ``just works''.
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70
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71 \begin{note}
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72 The Windows version of Mercurial does not automatically convert line
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73 endings between Windows and Unix styles. If you want to share work
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74 with Unix users, you must do a little additional configuration
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75 work. XXX Flesh this out.
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76 \end{note}
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77
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78 \section{Getting started}
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79
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80 To begin, we'll use the \hgcmd{version} command to find out whether
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81 Mercurial is actually installed properly. The actual version
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82 information that it prints isn't so important; it's whether it prints
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83 anything at all that we care about.
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84 \interaction{tour.version}
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85
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86 \subsection{Built-in help}
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87
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88 Mercurial provides a built-in help system. This invaluable for those
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89 times when you find yourself stuck trying to remember how to run a
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90 command. If you are completely stuck, simply run \hgcmd{help}; it
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91 will print a brief list of commands, along with a description of what
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92 each does. If you ask for help on a specific command (as below), it
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93 prints more detailed information.
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94 \interaction{tour.help}
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95 For a more impressive level of detail (which you won't usually need)
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96 run \hgcmdargs{help}{\hggopt{-v}}. The \hggopt{-v} option is short
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97 for \hggopt{--verbose}, and tells Mercurial to print more information
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98 than it usually would.
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99
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100 \section{Working with a repository}
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101
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102 In Mercurial, everything happens inside a \emph{repository}. The
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103 repository for a project contains all of the files that ``belong to''
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104 that project, along with a historical record of the project's files.
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105
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106 There's nothing particularly magical about a repository; it is simply
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107 a directory tree in your filesystem that Mercurial treats as special.
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108 You can rename delete a repository any time you like, using either the
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109 command line or your file browser.
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110
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111 \subsection{Making a local copy of a repository}
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112
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113 \emph{Copying} a repository is just a little bit special. While you
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114 could use a normal file copying command to make a copy of a
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115 repository, it's best to use a built-in command that Mercurial
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116 provides. This command is called \hgcmd{clone}, because it creates an
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117 identical copy of an existing repository.
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118 \interaction{tour.clone}
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119 If our clone succeeded, we should now have a local directory called
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120 \dirname{hello}. This directory will contain some files.
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121 \interaction{tour.ls}
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122 These files have the same contents and history in our repository as
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123 they do in the repository we cloned.
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124
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125 Every Mercurial repository is complete, self-contained, and
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126 independent. It contains its own private copy of a project's files
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127 and history. A cloned repository remembers the location of the
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128 repository it was cloned from, but it does not communicate with that
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129 repository, or any other, unless you tell it to.
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130
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131 What this means for now is that we're free to experiment with our
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132 repository, safe in the knowledge that it's a private ``sandbox'' that
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133 won't affect anyone else.
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134
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135 \subsection{What's in a repository?}
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136
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137 When we take a more detailed look inside a repository, we can see that
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138 it contains a directory named \dirname{.hg}. This is where Mercurial
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139 keeps all of its metadata for the repository.
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140 \interaction{tour.ls-a}
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141
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142 The contents of the \dirname{.hg} directory and its subdirectories are
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143 private to Mercurial. Every other file and directory in the
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144 repository is yours to do with as you please.
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145
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146 To introduce a little terminology, the \dirname{.hg} directory is the
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147 ``real'' repository, and all of the files and directories that coexist
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148 with it are said to live in the \emph{working directory}. An easy way
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149 to remember the distinction is that the \emph{repository} contains the
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150 \emph{history} of your project, while the \emph{working directory}
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151 contains a \emph{snapshot} of your project at a particular point in
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152 history.
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153
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154 \section{A tour through history}
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155
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156 One of the first things we might want to do with a new, unfamiliar
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157 repository is understand its history. The \hgcmd{log} command gives
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158 us a view of history.
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159 \interaction{tour.log}
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160 By default, this command prints a brief paragraph of output for each
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161 change to the project that was recorded. In Mercurial terminology, we
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162 call each of these recorded events a \emph{changeset}, because it can
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163 contain a record of changes to several files.
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164
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165 The fields in a record of output from \hgcmd{log} are as follows.
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166 \begin{itemize}
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167 \item[\texttt{changeset}] This field has the format of a number,
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168 followed by a colon, followed by a hexadecimal string. These are
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169 \emph{identifiers} for the changeset. There are two identifiers
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170 because the number is shorter and easier to type than the hex
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171 string.
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172 \item[\texttt{user}] The identity of the person who created the
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173 changeset. This is a free-form field, but it most often contains a
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174 person's name and email address.
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175 \item[\texttt{date}] The date and time on which the changeset was
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176 created, and the timezone in which it was created. (Thef date and
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177 time are local to that timezone; they display what time and date it
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178 was for the person who created the changeset.)
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179 \item[\texttt{summary}] The first line of the text message that the
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180 creator of the changeset entered to describe the changeset.
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181 \end{itemize}
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182 The default output printed by \hgcmd{log} is purely a summary; it is
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183 missing a lot of detail.
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184
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185 \subsection{Changesets, revisions, and identification}
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186
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187 English being a notoriously sloppy language, we have a variety of
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188 terms that have the same meaning. If you are talking about Mercurial
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189 history with other people, you will find that the word ``changeset''
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190 is often compressed to ``change'' or ``cset'', and sometimes a
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191 changeset is referred to as a ``revision'' or a ``rev''.
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192
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193 While it doesn't matter what \emph{word} you use to refer to the
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194 concept of ``a~changeset'', the \emph{identifier} that you use to
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195 refer to ``a~\emph{specific} changeset'' is of great importance.
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196 Recall that the \texttt{changeset} field in the output from
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197 \hgcmd{log} identifies a changeset using both a number and a
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198 hexadecimal string. The number is \emph{only valid in that
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199 repository}, while the hex string is the \emph{permanent, unchanging
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200 identifier} that will always identify that changeset in every copy
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201 of the repository.
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202
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203 This distinction is important. If you send someone an email talking
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204 about ``revision~33'', there's a high likelihood that their
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205 revision~33 will \emph{not be the same} as yours. The reason for this
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206 is that a revision number depends on the order in which changes
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207 arrived in a repository, and there is no guarantee that the same
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208 changes will happen in the same order in different repositories.
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209 Three changes $a,b,c$ can easily appear in one repository as $0,1,2$,
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210 while in another as $1,0,2$.
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211
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212 Mercurial uses revision numbers purely as a convenient shorthand. If
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213 you need to discuss a changeset with someone, or make a record of a
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214 changeset for some other reason (for example, in a bug report), use
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215 the hexadecimal identifier.
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216
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217 \subsection{Viewing specific revisions}
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218
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219 To narrow the output of \hgcmd{log} down to a single revision, use the
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220 \hgopt{log}{-r} (or \hgopt{log}{--rev}) option. You can use either a
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221 revision number or a long-form changeset identifier, and you can
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222 provide as many revisions as you want. \interaction{tour.log-r}
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223
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224 If you want to see the history of several revisions without having to
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225 list each one, you can use \emph{range notation}; this lets you
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226 express the idea ``I want all revisions between $a$ and $b$,
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227 inclusive''.
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228 \interaction{tour.log.range}
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229 Mercurial also honours the order in which you specify revisions, so
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230 \hgcmdargs{log}{-r 2:4} prints $2,3,4$ while \hgcmdargs{log}{-r 4:2}
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231 prints $4,3,2$.
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232
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233 \subsection{More detailed information}
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234
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235 While the summary information printed by \hgcmd{log} is useful if you
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236 already know what you're looking for, you may need to see a complete
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237 description of the change, or a list of the files changed, if you're
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238 trying to decide whether a changeset is the one you're looking for.
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239 The \hgcmd{log} command's \hggopt{-v} (or \hggopt{--verbose})
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240 option gives you this extra detail.
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241 \interaction{tour.log-v}
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242
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243 If you want to see both the description and content of a change, add
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244 the \hgopt{log}{-p} (or \hgopt{log}{--patch}) option. This displays
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245 the content of a change as a \emph{unified diff} (if you've never seen
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246 a unified diff before, see section~\ref{sec:mq:patch} for an overview).
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247 \interaction{tour.log-vp}
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248
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249 \section{All about command options}
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250
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251 Let's take a brief break from exploring Mercurial commands to discuss
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252 a pattern in the way that they work; you may find this useful to keep
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253 in mind as we continiue our tour.
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254
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255 Mercurial has a consistent and straightforward approach to dealing
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256 with the options that you can pass to commands. It follows the
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257 conventions for options that are common to modern Linux and Unix
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258 systems.
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259 \begin{itemize}
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260 \item Every option has a long name. For example, as we've already
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261 seen, the \hgcmd{log} command accepts a \hgopt{log}{--rev} option.
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262 \item Most options have short names, too. Instead of
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263 \hgopt{log}{--rev}, we can use \hgopt{log}{-r}. (The reason that
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264 some options don't have short names is that the options in question
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265 are rarely used.)
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266 \item Long options start with two dashes (e.g.~\hgopt{log}{--rev}),
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267 while short options start with one (e.g.~\hgopt{log}{-r}).
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268 \item Option naming and usage is consistent across commands. For
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269 example, every command that lets you specify a changeset~ID or
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270 revision number accepts both \hgopt{log}{-r} and \hgopt{log}{--rev}
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271 arguments.
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272 \end{itemize}
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273 In the examples throughout this book, I use short options instead of
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274 long. This just reflects my own preference, so don't read anything
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275 significant into it.
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276
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277 Most commands that print output of some kind will print more output
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278 when passed a \hggopt{-v} (or \hggopt{--verbose}) option, and less
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279 when passed \hggopt{-q} (or \hggopt{--quiet}).
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280
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281 \section{Making and reviewing changes}
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282
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283 Now that we have a grasp of viewing history in Mercurial, let's take a
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284 look at making some changes and examining them.
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285
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286 The first thing we'll do is isolate our experiment in a repository of
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287 its own. We use the \hgcmd{clone} command, but we don't need to
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288 clone a copy of the remote repository. Since we already have a copy
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289 of it locally, we can just clone that instead. This is much faster
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290 than cloning over the network, and cloning a local repository uses
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291 less disk space in most cases, too.
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292 \interaction{tour.reclone}
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293 As an aside, it's often good practice to keep a ``pristine'' copy of a
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294 remote repository around, which you can then make temporary clones of
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295 to create sandboxes for each task you want to work on. This lets you
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296 work on multiple tasks in parallel, each isolated from the others
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297 until it's complete and you're ready to integrate it back. Because
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298 local clones are so cheap, there's almost no overhead to cloning and
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299 destroying repositories whenever you want.
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300
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301 In our \dirname{my-hello} repository, we have a file
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302 \filename{hello.c} that contains the classic ``hello, world'' program.
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303 Let's use the ancient and venerable \command{sed} command to edit this
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304 file so that it prints a second line of output. (I'm only using
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305 \command{sed} to do this because it's easy to write a scripted example
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306 this way. Since you're not under the same constraint, you probably
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307 won't want to use \command{sed}; simply use your preferred text editor to
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308 do the same thing.)
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309 \interaction{tour.sed}
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310
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311 Mercurial's \hgcmd{status} command will tell us what Mercurial knows
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312 about the files in the repository.
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313 \interaction{tour.status}
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314 The \hgcmd{status} command prints no output for some files, but a line
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315 starting with ``\texttt{M}'' for \filename{hello.c}. Unless you tell
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316 it to, \hgcmd{status} will not print any output for files that have
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317 not been modified.
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318
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319 The ``\texttt{M}'' indicates that Mercurial has noticed that we
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320 modified \filename{hello.c}. Notice that we didn't need to
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321 \emph{inform} Mercurial that we were going to modify the file before
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322 we started, or that we had modified the file after we were done; it
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323 was able to figure this out itself.
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324
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325 It's a little bit helpful to know that we've modified
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326 \filename{hello.c}, but we might prefer to know exactly \emph{what}
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327 changes we've made to it. To do this, we use the \hgcmd{diff}
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328 command.
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329 \interaction{tour.diff}
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330
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331 \section{Recording changes in a new changeset}
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332
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333 We can modify files, build and test our changes, and use
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334 \hgcmd{status} and \hgcmd{diff} to review our changes, until we're
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335 satisfied with what we've done and arrive at a natural stopping point
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336 where we want to record our work in a new changeset.
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337
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338 The \hgcmd{commit} command lets us create a new changeset; we'll
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339 usually refer to this as ``making a commit'' or ``committing''.
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340
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341 \subsection{Writing a commit message}
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342
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343 When we commit a change, Mercurial drops us into a text editor, to
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344 enter a message that will describe the modifications we've made in
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345 this changeset. This is called the \emph{commit message}. It will be
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346 a record for readers of what we did and why, and it will be printed by
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347 \hgcmd{log} after we've finished committing.
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348 \interaction{tour.commit}
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349
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350 The editor that the \hgcmd{commit} command drops us into will contain
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351 an empty line, followed by a number of lines starting with
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352 ``\texttt{HG:}''.
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353 \begin{codesample2}
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354 \emph{empty line}
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355 HG: changed hello.c
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356 \end{codesample2}
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357 Mercurial ignores the lines that start with ``\texttt{HG:}''; it uses
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358 them only to tell us which files it's recording changes to. Modifying
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359 or deleting these lines has no effect.
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360
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361 \subsection{Writing a good commit message}
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362
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363 Since \hgcmd{log} only prints the first line of a commit message by
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364 default, it's best to write a commit message whose first line stands
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365 alone. Here's a real example of a commit message that \emph{doesn't}
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366 follow this guideline, and hence has a summary that is not readable.
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367 \begin{codesample2}
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368 changeset: 73:584af0e231be
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369 user: Censored Person <censored.person@example.org>
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370 date: Tue Sep 26 21:37:07 2006 -0700
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371 summary: include buildmeister/commondefs. Add an exports and install
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372 \end{codesample2}
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373
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374 As far as the remainder of the contents of the commit message are
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375 concerned, there are no hard-and-fast rules. Mercurial itself doesn't
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376 interpret or care about the contents of the commit message, though
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377 your project may have policies that dictate a certain kind of
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378 formatting.
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379
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380 My personal preference is for short, but informative, commit messages
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381 that tell me something that I can't figure out with a quick glance at
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382 the output of \hgcmdargs{log}{--patch}.
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383
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384 \subsection{Aborting a commit}
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385
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386 If you decide that you don't want to commit while in the middle of
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387 editing a commit message, simply exit from your editor without saving
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388 the file that it's editing. This will cause nothing to happen to
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389 either the repository or the working directory.
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390
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391 If we run the \hgcmd{commit} command without any arguments, it records
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392 all of the changes we've made, as reported by \hgcmd{status} and
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393 \hgcmd{diff}.
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394
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395 \subsection{Admiring our new handywork}
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396
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397 Once we've finished the commit, we can use the \hgcmd{tip} command to
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398 display the changeset we just created. This command produces output
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399 that is identical to \hgcmd{log}, but it only displays the newest
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400 revision in the repository.
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401 \interaction{tour.tip}
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402 We refer to the newest revision in the repository as the tip revision,
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403 or simply the tip.
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404
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405 \section{Sharing changes}
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406
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407 We mentioned earlier that repositories in Mercurial are
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408 self-contained. This means that the changeset we just created exists
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409 only in our \dirname{my-hello} repository. Let's look at a few ways
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410 that we can propagate this change into other repositories.
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411
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412 \subsection{Pulling changes from another repository}
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413 \label{sec:tour:pull}
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414
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415 To get started, let's clone our original \dirname{hello} repository,
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416 which does not contain the change we just committed. We'll call our
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417 temporary repository \dirname{hello-pull}.
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418 \interaction{tour.clone-pull}
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419
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420 We'll use the \hgcmd{pull} command to bring changes from
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421 \dirname{my-hello} into \dirname{hello-pull}. However, blindly
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422 pulling unknown changes into a repository is a somewhat scary
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423 prospect. Mercurial provides the \hgcmd{incoming} command to tell us
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424 what changes the \hgcmd{pull} command \emph{would} pull into the
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425 repository, without actually pulling the changes in.
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426 \interaction{tour.incoming}
|
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bos@91
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427 (Of course, someone could cause more changesets to appear in the
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428 repository that we ran \hgcmd{incoming} in, before we get a chance to
|
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bos@91
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429 \hgcmd{pull} the changes, so that we could end up pulling changes that we
|
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430 didn't expect.)
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431
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432 Bringing changes into a repository is a simple matter of running the
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433 \hgcmd{pull} command, and telling it which repository to pull from.
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bos@91
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434 \interaction{tour.pull}
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435 As you can see from the before-and-after output of \hgcmd{tip}, we
|
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436 have successfully pulled changes into our repository. There remains
|
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437 one step before we can see these changes in the working directory.
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438
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439 \subsection{Updating the working directory}
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440
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441 We have so far glossed over the relationship between a repository and
|
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442 its working directory. The \hgcmd{pull} command that we ran in
|
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443 section~\ref{sec:tour:pull} brought changes into the repository, but
|
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444 if we check, there's no sign of those changes in the working
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445 directory. This is because \hgcmd{pull} does not (by default) touch
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446 the working directory. Instead, we use the \hgcmd{update} command to
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447 do this.
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bos@91
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448 \interaction{tour.update}
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449
|
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bos@91
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450 It might seem a bit strange that \hgcmd{pull} doesn't update the
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451 working directory automatically. There's actually a good reason for
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452 this: you can use \hgcmd{update} to update the working directory to
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453 the state it was in at \emph{any revision} in the history of the
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454 repository. If you had the working directory updated to an old
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455 revision---to hunt down the origin of a bug, say---and ran a
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456 \hgcmd{pull} which automatically updated the working directory to a
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457 new revision, you might not be terribly happy.
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458
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bos@91
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459 However, since pull-then-update is such a common thing to do,
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460 Mercurial lets you combine the two by passing the \hgopt{pull}{-u}
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461 option to \hgcmd{pull}.
|
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462 \begin{codesample2}
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463 hg pull -u
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464 \end{codesample2}
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465 If you look back at the output of \hgcmd{pull} in
|
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466 section~\ref{sec:tour:pull} when we ran it without \hgopt{pull}{-u},
|
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467 you can see that it printed a helpful reminder that we'd have to take
|
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468 an explicit step to update the working directory:
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469 \begin{codesample2}
|
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bos@92
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470 (run 'hg update' to get a working copy)
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bos@92
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471 \end{codesample2}
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472
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473 To find out what revision the working directory is at, use the
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474 \hgcmd{parents} command.
|
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bos@91
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475 \interaction{tour.parents}
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bos@91
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476 To update the working directory to a particular revision, give a
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477 revision number or changeset~ID to the \hgcmd{update} command.
|
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bos@91
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478 \interaction{tour.older}
|
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bos@91
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479 If you omit an explicit revision, \hgcmd{update} will update to the
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480 tip revision, as shown by the second call to \hgcmd{update} in the
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481 example above.
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482
|
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bos@92
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483 \subsection{Pushing changes to another repository}
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484
|
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bos@92
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485 Mercurial lets us push changes to another repository, from the
|
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486 repository we're currently visiting. As with the example of
|
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487 \hgcmd{pull} above, we'll create a temporary repository to push our
|
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488 changes into.
|
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bos@92
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489 \interaction{tour.clone-push}
|
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bos@92
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490 The \hgcmd{outgoing} command tells us what changes would be pushed
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bos@92
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491 into another repository.
|
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bos@92
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492 \interaction{tour.outgoing}
|
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bos@92
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493 And the \hgcmd{push} command does the actual push.
|
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bos@92
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494 \interaction{tour.push}
|
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bos@92
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495 As with \hgcmd{pull}, the \hgcmd{push} command does not update the
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bos@92
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496 working directory in the repository that it's pushing changes into.
|
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bos@92
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497 (Unlike \hgcmd{pull}, \hgcmd{push} does not provide a \texttt{-u}
|
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bos@92
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498 option that updates the other repository's working directory.)
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bos@92
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499
|
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bos@92
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500 What happens if we try to pull or push changes and the receiving
|
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bos@92
|
501 repository already has those changes? Nothing too exciting.
|
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502 \interaction{tour.push.nothing}
|
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bos@92
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503
|
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bos@93
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504 \subsection{Sharing changes over a network}
|
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bos@93
|
505
|
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bos@93
|
506 The commands we have covered in the previous few sections are not
|
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bos@93
|
507 limited to working with local repositories. Each works in exactly the
|
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bos@93
|
508 same fashion over a network connection; simply pass in a URL instead
|
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509 of a local path.
|
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bos@93
|
510 \interaction{tour.outgoing.net}
|
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bos@93
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511 In this example, we can see what changes we could push to the remote
|
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|
512 repository, but the repository is understandably not set up to let
|
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|
513 anonymous users push to it.
|
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bos@93
|
514 \interaction{tour.push.net}
|
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bos@93
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515
|
|
bos@84
|
516 %%% Local Variables:
|
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bos@84
|
517 %%% mode: latex
|
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bos@84
|
518 %%% TeX-master: "00book"
|
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bos@84
|
519 %%% End:
|
