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1 <!-- vim: set filetype=docbkxml shiftwidth=2 autoindent expandtab tw=77 : -->
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2
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3 <chapter id="chap:daily">
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4 <title>Mercurial in daily use</title>
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5
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6 <sect1>
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7 <title>Telling Mercurial which files to track</title>
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8
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9 <para>Mercurial does not work with files in your repository unless
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10 you tell it to manage them. The <command role="hg-cmd">hg
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11 status</command> command will tell you which files Mercurial
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12 doesn't know about; it uses a
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13 <quote><literal>?</literal></quote> to display such
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14 files.</para>
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15
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16 <para>To tell Mercurial to track a file, use the <command
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17 role="hg-cmd">hg add</command> command. Once you have added a
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18 file, the entry in the output of <command role="hg-cmd">hg
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19 status</command> for that file changes from
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20 <quote><literal>?</literal></quote> to
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21 <quote><literal>A</literal></quote>.</para>
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22
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23 &interaction.daily.files.add;
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24
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25 <para>After you run a <command role="hg-cmd">hg commit</command>,
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26 the files that you added before the commit will no longer be
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27 listed in the output of <command role="hg-cmd">hg
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28 status</command>. The reason for this is that <command
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29 role="hg-cmd">hg status</command> only tells you about
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30 <quote>interesting</quote> files&emdash;those that you have
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31 modified or told Mercurial to do something with&emdash;by
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32 default. If you have a repository that contains thousands of
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33 files, you will rarely want to know about files that Mercurial
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34 is tracking, but that have not changed. (You can still get this
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35 information; we'll return to this later.)</para>
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36
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37 <para>Once you add a file, Mercurial doesn't do anything with it
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38 immediately. Instead, it will take a snapshot of the file's
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39 state the next time you perform a commit. It will then continue
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40 to track the changes you make to the file every time you commit,
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41 until you remove the file.</para>
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42
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43 <sect2>
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44 <title>Explicit versus implicit file naming</title>
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45
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46 <para>A useful behaviour that Mercurial has is that if you pass
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47 the name of a directory to a command, every Mercurial command
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48 will treat this as <quote>I want to operate on every file in
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49 this directory and its subdirectories</quote>.</para>
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50
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51 &interaction.daily.files.add-dir;
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52
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53 <para>Notice in this example that Mercurial printed the names of
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54 the files it added, whereas it didn't do so when we added the
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55 file named <filename>a</filename> in the earlier
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56 example.</para>
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57
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58 <para>What's going on is that in the former case, we explicitly
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59 named the file to add on the command line, so the assumption
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60 that Mercurial makes in such cases is that you know what you
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61 were doing, and it doesn't print any output.</para>
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62
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63 <para>However, when we <emphasis>imply</emphasis> the names of
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64 files by giving the name of a directory, Mercurial takes the
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65 extra step of printing the name of each file that it does
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66 something with. This makes it more clear what is happening,
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67 and reduces the likelihood of a silent and nasty surprise.
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68 This behaviour is common to most Mercurial commands.</para>
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69
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70 </sect2>
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71 <sect2>
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72 <title>Aside: Mercurial tracks files, not directories</title>
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73
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74 <para>Mercurial does not track directory information. Instead,
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75 it tracks the path to a file. Before creating a file, it
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76 first creates any missing directory components of the path.
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77 After it deletes a file, it then deletes any empty directories
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78 that were in the deleted file's path. This sounds like a
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79 trivial distinction, but it has one minor practical
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80 consequence: it is not possible to represent a completely
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81 empty directory in Mercurial.</para>
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82
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83 <para>Empty directories are rarely useful, and there are
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84 unintrusive workarounds that you can use to achieve an
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85 appropriate effect. The developers of Mercurial thus felt
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86 that the complexity that would be required to manage empty
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87 directories was not worth the limited benefit this feature
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88 would bring.</para>
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89
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90 <para>If you need an empty directory in your repository, there
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91 are a few ways to achieve this. One is to create a directory,
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92 then <command role="hg-cmd">hg add</command> a
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93 <quote>hidden</quote> file to that directory. On Unix-like
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94 systems, any file name that begins with a period
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95 (<quote><literal>.</literal></quote>) is treated as hidden by
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96 most commands and GUI tools. This approach is illustrated
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97 below.</para>
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98
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99 &interaction.daily.files.hidden;
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100
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101 <para>Another way to tackle a need for an empty directory is to
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102 simply create one in your automated build scripts before they
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103 will need it.</para>
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104
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105 </sect2>
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106 </sect1>
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107 <sect1>
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108 <title>How to stop tracking a file</title>
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109
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110 <para>Once you decide that a file no longer belongs in your
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111 repository, use the <command role="hg-cmd">hg remove</command>
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112 command; this deletes the file, and tells Mercurial to stop
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113 tracking it. A removed file is represented in the output of
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114 <command role="hg-cmd">hg status</command> with a
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115 <quote><literal>R</literal></quote>.</para>
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116
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117 &interaction.daily.files.remove;
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118
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119 <para>After you <command role="hg-cmd">hg remove</command> a file,
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120 Mercurial will no longer track changes to that file, even if you
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121 recreate a file with the same name in your working directory.
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122 If you do recreate a file with the same name and want Mercurial
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123 to track the new file, simply <command role="hg-cmd">hg
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124 add</command> it. Mercurial will know that the newly added
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125 file is not related to the old file of the same name.</para>
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126
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127 <sect2>
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128 <title>Removing a file does not affect its history</title>
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129
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130 <para>It is important to understand that removing a file has
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131 only two effects.</para>
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132 <itemizedlist>
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133 <listitem><para>It removes the current version of the file
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134 from the working directory.</para>
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135 </listitem>
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136 <listitem><para>It stops Mercurial from tracking changes to
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137 the file, from the time of the next commit.</para>
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138 </listitem></itemizedlist>
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139 <para>Removing a file <emphasis>does not</emphasis> in any way
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140 alter the <emphasis>history</emphasis> of the file.</para>
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141
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142 <para>If you update the working directory to a changeset in
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143 which a file that you have removed was still tracked, it will
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144 reappear in the working directory, with the contents it had
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145 when you committed that changeset. If you then update the
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146 working directory to a later changeset, in which the file had
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147 been removed, Mercurial will once again remove the file from
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148 the working directory.</para>
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149
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150 </sect2>
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151 <sect2>
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152 <title>Missing files</title>
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153
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154 <para>Mercurial considers a file that you have deleted, but not
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155 used <command role="hg-cmd">hg remove</command> to delete, to
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156 be <emphasis>missing</emphasis>. A missing file is
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157 represented with <quote><literal>!</literal></quote> in the
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158 output of <command role="hg-cmd">hg status</command>.
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159 Mercurial commands will not generally do anything with missing
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160 files.</para>
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161
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162 &interaction.daily.files.missing;
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163
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164 <para>If your repository contains a file that <command
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165 role="hg-cmd">hg status</command> reports as missing, and
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166 you want the file to stay gone, you can run <command
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167 role="hg-cmd">hg remove <option
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168 role="hg-opt-remove">--after</option></command> at any
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169 time later on, to tell Mercurial that you really did mean to
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170 remove the file.</para>
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171
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172 &interaction.daily.files.remove-after;
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173
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174 <para>On the other hand, if you deleted the missing file by
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175 accident, give <command role="hg-cmd">hg revert</command> the
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176 name of the file to recover. It will reappear, in unmodified
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177 form.</para>
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178
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179 &interaction.daily.files.recover-missing;
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180
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181 </sect2>
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182 <sect2>
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183 <title>Aside: why tell Mercurial explicitly to remove a
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184 file?</title>
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185
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186 <para>You might wonder why Mercurial requires you to explicitly
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187 tell it that you are deleting a file. Early during the
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188 development of Mercurial, it let you delete a file however you
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189 pleased; Mercurial would notice the absence of the file
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190 automatically when you next ran a <command role="hg-cmd">hg
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191 commit</command>, and stop tracking the file. In practice,
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192 this made it too easy to accidentally remove a file without
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193 noticing.</para>
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194
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195 </sect2>
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196 <sect2>
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197 <title>Useful shorthand&emdash;adding and removing files in one
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198 step</title>
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199
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200 <para>Mercurial offers a combination command, <command
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201 role="hg-cmd">hg addremove</command>, that adds untracked
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202 files and marks missing files as removed.</para>
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203
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204 &interaction.daily.files.addremove;
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205
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206 <para>The <command role="hg-cmd">hg commit</command> command
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207 also provides a <option role="hg-opt-commit">-A</option>
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208 option that performs this same add-and-remove, immediately
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209 followed by a commit.</para>
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210
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211 &interaction.daily.files.commit-addremove;
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212
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213 </sect2>
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214 </sect1>
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215 <sect1>
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216 <title>Copying files</title>
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217
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218 <para>Mercurial provides a <command role="hg-cmd">hg
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219 copy</command> command that lets you make a new copy of a
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220 file. When you copy a file using this command, Mercurial makes
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221 a record of the fact that the new file is a copy of the original
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222 file. It treats these copied files specially when you merge
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223 your work with someone else's.</para>
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224
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225 <sect2>
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226 <title>The results of copying during a merge</title>
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227
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228 <para>What happens during a merge is that changes
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229 <quote>follow</quote> a copy. To best illustrate what this
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230 means, let's create an example. We'll start with the usual
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231 tiny repository that contains a single file.</para>
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232
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233 &interaction.daily.copy.init;
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234
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235 <para>We need to do some work in
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236 parallel, so that we'll have something to merge. So let's
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237 clone our repository.</para>
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238
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239 &interaction.daily.copy.clone;
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240
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241 <para>Back in our initial repository, let's use the <command
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242 role="hg-cmd">hg copy</command> command to make a copy of
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243 the first file we created.</para>
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244
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245 &interaction.daily.copy.copy;
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246
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247 <para>If we look at the output of the <command role="hg-cmd">hg
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248 status</command> command afterwards, the copied file looks
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249 just like a normal added file.</para>
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250
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251 &interaction.daily.copy.status;
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252
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253 <para>But if we pass the <option
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254 role="hg-opt-status">-C</option> option to <command
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255 role="hg-cmd">hg status</command>, it prints another line of
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256 output: this is the file that our newly-added file was copied
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257 <emphasis>from</emphasis>.</para>
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258
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259 &interaction.daily.copy.status-copy;
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260
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261 <para>Now, back in the repository we cloned, let's make a change
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262 in parallel. We'll add a line of content to the original file
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263 that we created.</para>
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264
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265 &interaction.daily.copy.other;
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266
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267 <para>Now we have a modified <filename>file</filename> in this
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268 repository. When we pull the changes from the first
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269 repository, and merge the two heads, Mercurial will propagate
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270 the changes that we made locally to <filename>file</filename>
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271 into its copy, <filename>new-file</filename>.</para>
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272
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273 &interaction.daily.copy.merge;
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274
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275 </sect2>
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276 <sect2 id="sec:daily:why-copy">
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277 <title>Why should changes follow copies?</title>
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278
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279 <para>This behaviour, of changes to a file propagating out to
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280 copies of the file, might seem esoteric, but in most cases
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281 it's highly desirable.</para>
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282
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283 <para>First of all, remember that this propagation
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284 <emphasis>only</emphasis> happens when you merge. So if you
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285 <command role="hg-cmd">hg copy</command> a file, and
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286 subsequently modify the original file during the normal course
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287 of your work, nothing will happen.</para>
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288
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289 <para>The second thing to know is that modifications will only
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290 propagate across a copy as long as the repository that you're
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291 pulling changes from <emphasis>doesn't know</emphasis> about
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292 the copy.</para>
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293
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294 <para>The reason that Mercurial does this is as follows. Let's
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295 say I make an important bug fix in a source file, and commit
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296 my changes. Meanwhile, you've decided to <command
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297 role="hg-cmd">hg copy</command> the file in your repository,
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298 without knowing about the bug or having seen the fix, and you
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299 have started hacking on your copy of the file.</para>
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300
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301 <para>If you pulled and merged my changes, and Mercurial
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302 <emphasis>didn't</emphasis> propagate changes across copies,
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303 your source file would now contain the bug, and unless you
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304 remembered to propagate the bug fix by hand, the bug would
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305 <emphasis>remain</emphasis> in your copy of the file.</para>
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306
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307 <para>By automatically propagating the change that fixed the bug
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308 from the original file to the copy, Mercurial prevents this
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309 class of problem. To my knowledge, Mercurial is the
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310 <emphasis>only</emphasis> revision control system that
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311 propagates changes across copies like this.</para>
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312
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313 <para>Once your change history has a record that the copy and
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314 subsequent merge occurred, there's usually no further need to
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315 propagate changes from the original file to the copied file,
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316 and that's why Mercurial only propagates changes across copies
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317 until this point, and no further.</para>
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318
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319 </sect2>
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bos@559
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320 <sect2>
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321 <title>How to make changes <emphasis>not</emphasis> follow a
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322 copy</title>
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323
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324 <para>If, for some reason, you decide that this business of
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325 automatically propagating changes across copies is not for
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326 you, simply use your system's normal file copy command (on
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327 Unix-like systems, that's <command>cp</command>) to make a
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328 copy of a file, then <command role="hg-cmd">hg add</command>
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329 the new copy by hand. Before you do so, though, please do
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330 reread section <xref linkend="sec:daily:why-copy"/>, and make
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331 an informed
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332 decision that this behaviour is not appropriate to your
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333 specific case.</para>
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334
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335 </sect2>
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bos@559
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336 <sect2>
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bos@559
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337 <title>Behaviour of the <command role="hg-cmd">hg copy</command>
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338 command</title>
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339
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bos@559
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340 <para>When you use the <command role="hg-cmd">hg copy</command>
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341 command, Mercurial makes a copy of each source file as it
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342 currently stands in the working directory. This means that if
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343 you make some modifications to a file, then <command
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344 role="hg-cmd">hg copy</command> it without first having
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345 committed those changes, the new copy will also contain the
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346 modifications you have made up until that point. (I find this
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347 behaviour a little counterintuitive, which is why I mention it
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348 here.)</para>
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349
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bos@559
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350 <para>The <command role="hg-cmd">hg copy</command> command acts
|
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bos@559
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351 similarly to the Unix <command>cp</command> command (you can
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352 use the <command role="hg-cmd">hg cp</command> alias if you
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353 prefer). The last argument is the
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354 <emphasis>destination</emphasis>, and all prior arguments are
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355 <emphasis>sources</emphasis>. If you pass it a single file as
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356 the source, and the destination does not exist, it creates a
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357 new file with that name.</para>
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358
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359 &interaction.daily.copy.simple;
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360
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bos@567
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361 <para>If the destination is a directory, Mercurial copies its
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362 sources into that directory.</para>
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363
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bos@567
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364 &interaction.daily.copy.dir-dest;
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365
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bos@567
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366 <para>Copying a directory is
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367 recursive, and preserves the directory structure of the
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368 source.</para>
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369
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370 &interaction.daily.copy.dir-src;
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371
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bos@567
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372 <para>If the source and destination are both directories, the
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373 source tree is recreated in the destination directory.</para>
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374
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375 &interaction.daily.copy.dir-src-dest;
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376
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bos@559
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377 <para>As with the <command role="hg-cmd">hg rename</command>
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378 command, if you copy a file manually and then want Mercurial
|
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379 to know that you've copied the file, simply use the <option
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bos@559
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380 role="hg-opt-copy">--after</option> option to <command
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381 role="hg-cmd">hg copy</command>.</para>
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382
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bos@567
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383 &interaction.daily.copy.after;
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384
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bos@559
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385 </sect2>
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bos@559
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386 </sect1>
|
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bos@559
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387 <sect1>
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bos@559
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388 <title>Renaming files</title>
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389
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390 <para>It's rather more common to need to rename a file than to
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391 make a copy of it. The reason I discussed the <command
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392 role="hg-cmd">hg copy</command> command before talking about
|
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bos@559
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393 renaming files is that Mercurial treats a rename in essentially
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bos@559
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394 the same way as a copy. Therefore, knowing what Mercurial does
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395 when you copy a file tells you what to expect when you rename a
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bos@559
|
396 file.</para>
|
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bos@559
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397
|
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bos@559
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398 <para>When you use the <command role="hg-cmd">hg rename</command>
|
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bos@559
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399 command, Mercurial makes a copy of each source file, then
|
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bos@567
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400 deletes it and marks the file as removed.</para>
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bos@567
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401
|
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bos@567
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402 &interaction.daily.rename.rename;
|
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bos@567
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403
|
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bos@567
|
404 <para>The <command role="hg-cmd">hg status</command> command shows
|
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bos@567
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405 the newly copied file as added, and the copied-from file as
|
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bos@567
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406 removed.</para>
|
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bos@567
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407
|
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bos@567
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408 &interaction.daily.rename.status;
|
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bos@567
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409
|
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bos@567
|
410 <para>As with the results of a <command role="hg-cmd">hg
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411 copy</command>, we must use the <option
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bos@567
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412 role="hg-opt-status">-C</option> option to <command
|
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bos@559
|
413 role="hg-cmd">hg status</command> to see that the added file
|
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bos@559
|
414 is really being tracked by Mercurial as a copy of the original,
|
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bos@567
|
415 now removed, file.</para>
|
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bos@567
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416
|
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bos@567
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417 &interaction.daily.rename.status-copy;
|
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bos@559
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418
|
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bos@559
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419 <para>As with <command role="hg-cmd">hg remove</command> and
|
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bos@559
|
420 <command role="hg-cmd">hg copy</command>, you can tell Mercurial
|
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bos@559
|
421 about a rename after the fact using the <option
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bos@559
|
422 role="hg-opt-rename">--after</option> option. In most other
|
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bos@559
|
423 respects, the behaviour of the <command role="hg-cmd">hg
|
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bos@559
|
424 rename</command> command, and the options it accepts, are
|
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bos@559
|
425 similar to the <command role="hg-cmd">hg copy</command>
|
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bos@559
|
426 command.</para>
|
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bos@559
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427
|
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bos@559
|
428 <sect2>
|
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bos@559
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429 <title>Renaming files and merging changes</title>
|
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bos@559
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430
|
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bos@559
|
431 <para>Since Mercurial's rename is implemented as
|
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bos@559
|
432 copy-and-remove, the same propagation of changes happens when
|
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bos@559
|
433 you merge after a rename as after a copy.</para>
|
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bos@559
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434
|
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bos@559
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435 <para>If I modify a file, and you rename it to a new name, and
|
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bos@559
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436 then we merge our respective changes, my modifications to the
|
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bos@559
|
437 file under its original name will be propagated into the file
|
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bos@559
|
438 under its new name. (This is something you might expect to
|
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bos@559
|
439 <quote>simply work,</quote> but not all revision control
|
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bos@559
|
440 systems actually do this.)</para>
|
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bos@559
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441
|
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bos@559
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442 <para>Whereas having changes follow a copy is a feature where
|
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bos@559
|
443 you can perhaps nod and say <quote>yes, that might be
|
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bos@559
|
444 useful,</quote> it should be clear that having them follow a
|
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bos@559
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445 rename is definitely important. Without this facility, it
|
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bos@559
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446 would simply be too easy for changes to become orphaned when
|
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bos@559
|
447 files are renamed.</para>
|
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bos@559
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448
|
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bos@559
|
449 </sect2>
|
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bos@559
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450 <sect2>
|
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bos@559
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451 <title>Divergent renames and merging</title>
|
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bos@559
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452
|
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bos@559
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453 <para>The case of diverging names occurs when two developers
|
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bos@559
|
454 start with a file&emdash;let's call it
|
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bos@559
|
455 <filename>foo</filename>&emdash;in their respective
|
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bos@559
|
456 repositories.</para>
|
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bos@559
|
457
|
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bos@567
|
458 &interaction.rename.divergent.clone;
|
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bos@567
|
459
|
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bos@567
|
460 <para>Anne renames the file to <filename>bar</filename>.</para>
|
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bos@567
|
461
|
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bos@567
|
462 &interaction.rename.divergent.rename.anne;
|
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bos@567
|
463
|
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bos@567
|
464 <para>Meanwhile, Bob renames it to
|
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bos@567
|
465 <filename>quux</filename>.</para>
|
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bos@567
|
466
|
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bos@567
|
467 &interaction.rename.divergent.rename.bob;
|
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bos@559
|
468
|
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bos@559
|
469 <para>I like to think of this as a conflict because each
|
|
bos@559
|
470 developer has expressed different intentions about what the
|
|
bos@559
|
471 file ought to be named.</para>
|
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bos@559
|
472
|
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bos@559
|
473 <para>What do you think should happen when they merge their
|
|
bos@559
|
474 work? Mercurial's actual behaviour is that it always preserves
|
|
bos@559
|
475 <emphasis>both</emphasis> names when it merges changesets that
|
|
bos@567
|
476 contain divergent renames.</para>
|
|
bos@567
|
477
|
|
bos@567
|
478 &interaction.rename.divergent.merge;
|
|
bos@559
|
479
|
|
bos@559
|
480 <para>Notice that Mercurial does warn about the divergent
|
|
bos@559
|
481 renames, but it leaves it up to you to do something about the
|
|
bos@559
|
482 divergence after the merge.</para>
|
|
bos@559
|
483
|
|
bos@559
|
484 </sect2>
|
|
bos@559
|
485 <sect2>
|
|
bos@559
|
486 <title>Convergent renames and merging</title>
|
|
bos@559
|
487
|
|
bos@559
|
488 <para>Another kind of rename conflict occurs when two people
|
|
bos@559
|
489 choose to rename different <emphasis>source</emphasis> files
|
|
bos@559
|
490 to the same <emphasis>destination</emphasis>. In this case,
|
|
bos@559
|
491 Mercurial runs its normal merge machinery, and lets you guide
|
|
bos@559
|
492 it to a suitable resolution.</para>
|
|
bos@559
|
493
|
|
bos@559
|
494 </sect2>
|
|
bos@559
|
495 <sect2>
|
|
bos@559
|
496 <title>Other name-related corner cases</title>
|
|
bos@559
|
497
|
|
bos@559
|
498 <para>Mercurial has a longstanding bug in which it fails to
|
|
bos@559
|
499 handle a merge where one side has a file with a given name,
|
|
bos@559
|
500 while another has a directory with the same name. This is
|
|
bos@559
|
501 documented as <ulink role="hg-bug"
|
|
bos@559
|
502 url="http://www.selenic.com/mercurial/bts/issue29">issue
|
|
bos@567
|
503 29</ulink>.</para>
|
|
bos@567
|
504
|
|
bos@567
|
505 &interaction.issue29.go;
|
|
bos@559
|
506
|
|
bos@559
|
507 </sect2>
|
|
bos@559
|
508 </sect1>
|
|
bos@559
|
509 <sect1>
|
|
bos@559
|
510 <title>Recovering from mistakes</title>
|
|
bos@559
|
511
|
|
bos@559
|
512 <para>Mercurial has some useful commands that will help you to
|
|
bos@559
|
513 recover from some common mistakes.</para>
|
|
bos@559
|
514
|
|
bos@559
|
515 <para>The <command role="hg-cmd">hg revert</command> command lets
|
|
bos@559
|
516 you undo changes that you have made to your working directory.
|
|
bos@559
|
517 For example, if you <command role="hg-cmd">hg add</command> a
|
|
bos@559
|
518 file by accident, just run <command role="hg-cmd">hg
|
|
bos@559
|
519 revert</command> with the name of the file you added, and
|
|
bos@559
|
520 while the file won't be touched in any way, it won't be tracked
|
|
bos@559
|
521 for adding by Mercurial any longer, either. You can also use
|
|
bos@559
|
522 <command role="hg-cmd">hg revert</command> to get rid of
|
|
bos@559
|
523 erroneous changes to a file.</para>
|
|
bos@559
|
524
|
|
bos@559
|
525 <para>It's useful to remember that the <command role="hg-cmd">hg
|
|
bos@559
|
526 revert</command> command is useful for changes that you have
|
|
bos@559
|
527 not yet committed. Once you've committed a change, if you
|
|
bos@559
|
528 decide it was a mistake, you can still do something about it,
|
|
bos@559
|
529 though your options may be more limited.</para>
|
|
bos@559
|
530
|
|
bos@559
|
531 <para>For more information about the <command role="hg-cmd">hg
|
|
bos@559
|
532 revert</command> command, and details about how to deal with
|
|
bos@559
|
533 changes you have already committed, see chapter <xref
|
|
bos@559
|
534 linkend="chap:undo"/>.</para>
|
|
bos@559
|
535
|
|
bos@559
|
536 </sect1>
|
|
bos@559
|
537 </chapter>
|
|
bos@559
|
538
|
|
bos@559
|
539 <!--
|
|
bos@559
|
540 local variables:
|
|
bos@559
|
541 sgml-parent-document: ("00book.xml" "book" "chapter")
|
|
bos@559
|
542 end:
|
|
bos@559
|
543 -->
|
