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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 <?dbhtml filename="mercurial-in-daily-use.html"?>
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5 <title>Mercurial in daily use</title>
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6
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7 <sect1>
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8 <title>Telling Mercurial which files to track</title>
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9
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10 <para id="x_1a3">Mercurial does not work with files in your repository unless
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11 you tell it to manage them. The <command role="hg-cmd">hg
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12 status</command> command will tell you which files Mercurial
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13 doesn't know about; it uses a
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14 <quote><literal>?</literal></quote> to display such
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15 files.</para>
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16
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17 <para id="x_1a4">To tell Mercurial to track a file, use the <command
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18 role="hg-cmd">hg add</command> command. Once you have added a
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19 file, the entry in the output of <command role="hg-cmd">hg
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20 status</command> for that file changes from
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21 <quote><literal>?</literal></quote> to
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22 <quote><literal>A</literal></quote>.</para>
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23
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24 &interaction.daily.files.add;
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25
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26 <para id="x_1a5">After you run a <command role="hg-cmd">hg commit</command>,
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27 the files that you added before the commit will no longer be
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28 listed in the output of <command role="hg-cmd">hg
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29 status</command>. The reason for this is that by default, <command
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30 role="hg-cmd">hg status</command> only tells you about
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31 <quote>interesting</quote> files&emdash;those that you have (for
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32 example) modified, removed, or renamed. If you have a repository
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33 that contains thousands of files, you will rarely want to know
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34 about files that Mercurial is tracking, but that have not
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35 changed. (You can still get this information; we'll return to
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36 this later.)</para>
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37
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38 <para id="x_1a6">Once you add a file, Mercurial doesn't do anything with it
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39 immediately. Instead, it will take a snapshot of the file's
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40 state the next time you perform a commit. It will then continue
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41 to track the changes you make to the file every time you commit,
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42 until you remove the file.</para>
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43
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44 <sect2>
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45 <title>Explicit versus implicit file naming</title>
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46
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47 <para id="x_1a7">A useful behavior that Mercurial has is that if you pass
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48 the name of a directory to a command, every Mercurial command
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49 will treat this as <quote>I want to operate on every file in
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50 this directory and its subdirectories</quote>.</para>
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51
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52 &interaction.daily.files.add-dir;
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53
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54 <para id="x_1a8">Notice in this example that Mercurial printed
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55 the names of the files it added, whereas it didn't do so when
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56 we added the file named <filename>myfile.txt</filename> in the
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57 earlier example.</para>
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58
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59 <para id="x_1a9">What's going on is that in the former case, we explicitly
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60 named the file to add on the command line. The assumption
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61 that Mercurial makes in such cases is that we know what we
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62 are doing, and it doesn't print any output.</para>
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63
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64 <para id="x_1aa">However, when we <emphasis>imply</emphasis> the names of
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65 files by giving the name of a directory, Mercurial takes the
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66 extra step of printing the name of each file that it does
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67 something with. This makes it more clear what is happening,
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68 and reduces the likelihood of a silent and nasty surprise.
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69 This behavior is common to most Mercurial commands.</para>
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70 </sect2>
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71
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72 <sect2>
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73 <title>Mercurial tracks files, not directories</title>
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74
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75 <para id="x_1ab">Mercurial does not track directory information. Instead,
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76 it tracks the path to a file. Before creating a file, it
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77 first creates any missing directory components of the path.
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78 After it deletes a file, it then deletes any empty directories
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79 that were in the deleted file's path. This sounds like a
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80 trivial distinction, but it has one minor practical
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81 consequence: it is not possible to represent a completely
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82 empty directory in Mercurial.</para>
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83
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84 <para id="x_1ac">Empty directories are rarely useful, and there are
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85 unintrusive workarounds that you can use to achieve an
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86 appropriate effect. The developers of Mercurial thus felt
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87 that the complexity that would be required to manage empty
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88 directories was not worth the limited benefit this feature
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89 would bring.</para>
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90
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91 <para id="x_1ad">If you need an empty directory in your repository, there
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92 are a few ways to achieve this. One is to create a directory,
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93 then <command role="hg-cmd">hg add</command> a
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94 <quote>hidden</quote> file to that directory. On Unix-like
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95 systems, any file name that begins with a period
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96 (<quote><literal>.</literal></quote>) is treated as hidden by
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97 most commands and GUI tools. This approach is illustrated
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98 below.</para>
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99
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100 &interaction.daily.files.hidden;
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101
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102 <para id="x_1ae">Another way to tackle a need for an empty directory is to
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103 simply create one in your automated build scripts before they
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104 will need it.</para>
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105 </sect2>
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106 </sect1>
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107
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108 <sect1>
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109 <title>How to stop tracking a file</title>
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110
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111 <para id="x_1af">Once you decide that a file no longer belongs in your
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112 repository, use the <command role="hg-cmd">hg remove</command>
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113 command. This deletes the file, and tells Mercurial to stop
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114 tracking it. A removed file is represented in the output of
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115 <command role="hg-cmd">hg status</command> with a
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116 <quote><literal>R</literal></quote>.</para>
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117
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118 &interaction.daily.files.remove;
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119
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120 <para id="x_1b0">After you <command role="hg-cmd">hg remove</command> a file,
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121 Mercurial will no longer track changes to that file, even if you
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122 recreate a file with the same name in your working directory.
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123 If you do recreate a file with the same name and want Mercurial
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124 to track the new file, simply <command role="hg-cmd">hg
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125 add</command> it. Mercurial will know that the newly added
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126 file is not related to the old file of the same name.</para>
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127
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128 <sect2>
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129 <title>Removing a file does not affect its history</title>
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130
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131 <para id="x_1b1">It is important to understand that removing a file has
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132 only two effects.</para>
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133 <itemizedlist>
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134 <listitem><para id="x_1b2">It removes the current version of the file
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135 from the working directory.</para>
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136 </listitem>
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137 <listitem><para id="x_1b3">It stops Mercurial from tracking changes to
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138 the file, from the time of the next commit.</para>
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139 </listitem></itemizedlist>
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140 <para id="x_1b4">Removing a file <emphasis>does not</emphasis> in any way
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141 alter the <emphasis>history</emphasis> of the file.</para>
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142
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143 <para id="x_1b5">If you update the working directory to a
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144 changeset that was committed when it was still tracking a file
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145 that you later removed, the file will reappear in the working
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146 directory, with the contents it had when you committed that
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147 changeset. If you then update the working directory to a
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148 later changeset, in which the file had been removed, Mercurial
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149 will once again remove the file from the working
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150 directory.</para>
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151 </sect2>
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152
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153 <sect2>
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154 <title>Missing files</title>
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155
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156 <para id="x_1b6">Mercurial considers a file that you have deleted, but not
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157 used <command role="hg-cmd">hg remove</command> to delete, to
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158 be <emphasis>missing</emphasis>. A missing file is
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159 represented with <quote><literal>!</literal></quote> in the
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160 output of <command role="hg-cmd">hg status</command>.
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161 Mercurial commands will not generally do anything with missing
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162 files.</para>
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163
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164 &interaction.daily.files.missing;
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165
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166 <para id="x_1b7">If your repository contains a file that <command
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167 role="hg-cmd">hg status</command> reports as missing, and
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168 you want the file to stay gone, you can run <command
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169 role="hg-cmd">hg remove <option
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170 role="hg-opt-remove">--after</option></command> at any
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171 time later on, to tell Mercurial that you really did mean to
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172 remove the file.</para>
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173
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174 &interaction.daily.files.remove-after;
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175
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176 <para id="x_1b8">On the other hand, if you deleted the missing file by
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177 accident, give <command role="hg-cmd">hg revert</command> the
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178 name of the file to recover. It will reappear, in unmodified
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179 form.</para>
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180
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181 &interaction.daily.files.recover-missing;
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182 </sect2>
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183
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184 <sect2>
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185 <title>Aside: why tell Mercurial explicitly to remove a
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186 file?</title>
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187
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188 <para id="x_1b9">You might wonder why Mercurial requires you to explicitly
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189 tell it that you are deleting a file. Early during the
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190 development of Mercurial, it let you delete a file however you
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191 pleased; Mercurial would notice the absence of the file
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192 automatically when you next ran a <command role="hg-cmd">hg
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193 commit</command>, and stop tracking the file. In practice,
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194 this made it too easy to accidentally remove a file without
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195 noticing.</para>
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196 </sect2>
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197
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198 <sect2>
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199 <title>Useful shorthand&emdash;adding and removing files in one
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200 step</title>
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201
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202 <para id="x_1ba">Mercurial offers a combination command, <command
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203 role="hg-cmd">hg addremove</command>, that adds untracked
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204 files and marks missing files as removed.</para>
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205
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206 &interaction.daily.files.addremove;
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207
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208 <para id="x_1bb">The <command role="hg-cmd">hg commit</command> command
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209 also provides a <option role="hg-opt-commit">-A</option>
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210 option that performs this same add-and-remove, immediately
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211 followed by a commit.</para>
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212
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213 &interaction.daily.files.commit-addremove;
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214 </sect2>
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215 </sect1>
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216
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217 <sect1>
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218 <title>Copying files</title>
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219
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220 <para id="x_1bc">Mercurial provides a <command role="hg-cmd">hg
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221 copy</command> command that lets you make a new copy of a
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222 file. When you copy a file using this command, Mercurial makes
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223 a record of the fact that the new file is a copy of the original
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224 file. It treats these copied files specially when you merge
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225 your work with someone else's.</para>
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226
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227 <sect2>
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228 <title>The results of copying during a merge</title>
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229
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230 <para id="x_1bd">What happens during a merge is that changes
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231 <quote>follow</quote> a copy. To best illustrate what this
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232 means, let's create an example. We'll start with the usual
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233 tiny repository that contains a single file.</para>
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234
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235 &interaction.daily.copy.init;
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236
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237 <para id="x_1be">We need to do some work in
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238 parallel, so that we'll have something to merge. So let's
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239 clone our repository.</para>
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240
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241 &interaction.daily.copy.clone;
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242
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243 <para id="x_1bf">Back in our initial repository, let's use the <command
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244 role="hg-cmd">hg copy</command> command to make a copy of
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245 the first file we created.</para>
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246
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247 &interaction.daily.copy.copy;
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248
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249 <para id="x_1c0">If we look at the output of the <command role="hg-cmd">hg
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250 status</command> command afterwards, the copied file looks
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251 just like a normal added file.</para>
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252
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253 &interaction.daily.copy.status;
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254
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255 <para id="x_1c1">But if we pass the <option
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256 role="hg-opt-status">-C</option> option to <command
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257 role="hg-cmd">hg status</command>, it prints another line of
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258 output: this is the file that our newly-added file was copied
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259 <emphasis>from</emphasis>.</para>
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260
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261 &interaction.daily.copy.status-copy;
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262
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263 <para id="x_1c2">Now, back in the repository we cloned, let's make a change
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264 in parallel. We'll add a line of content to the original file
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265 that we created.</para>
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266
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267 &interaction.daily.copy.other;
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268
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269 <para id="x_1c3">Now we have a modified <filename>file</filename> in this
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270 repository. When we pull the changes from the first
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271 repository, and merge the two heads, Mercurial will propagate
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272 the changes that we made locally to <filename>file</filename>
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273 into its copy, <filename>new-file</filename>.</para>
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274
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275 &interaction.daily.copy.merge;
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276 </sect2>
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277
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278 <sect2 id="sec:daily:why-copy">
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279 <title>Why should changes follow copies?</title>
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280
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281 <para id="x_1c4">This behavior&emdash;of changes to a file
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282 propagating out to copies of the file&emdash;might seem
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283 esoteric, but in most cases it's highly desirable.</para>
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284
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285 <para id="x_1c5">First of all, remember that this propagation
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286 <emphasis>only</emphasis> happens when you merge. So if you
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287 <command role="hg-cmd">hg copy</command> a file, and
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288 subsequently modify the original file during the normal course
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289 of your work, nothing will happen.</para>
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290
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291 <para id="x_1c6">The second thing to know is that modifications will only
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292 propagate across a copy as long as the changeset that you're
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293 merging changes from <emphasis>hasn't yet seen</emphasis>
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294 the copy.</para>
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295
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296 <para id="x_1c7">The reason that Mercurial does this is as follows. Let's
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297 say I make an important bug fix in a source file, and commit
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298 my changes. Meanwhile, you've decided to <command
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299 role="hg-cmd">hg copy</command> the file in your repository,
|
|
bos@559
|
300 without knowing about the bug or having seen the fix, and you
|
|
bos@559
|
301 have started hacking on your copy of the file.</para>
|
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bos@559
|
302
|
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bos@584
|
303 <para id="x_1c8">If you pulled and merged my changes, and Mercurial
|
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bos@559
|
304 <emphasis>didn't</emphasis> propagate changes across copies,
|
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bos@674
|
305 your new source file would now contain the bug, and unless you
|
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bos@674
|
306 knew to propagate the bug fix by hand, the bug would
|
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bos@559
|
307 <emphasis>remain</emphasis> in your copy of the file.</para>
|
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bos@559
|
308
|
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bos@584
|
309 <para id="x_1c9">By automatically propagating the change that fixed the bug
|
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bos@559
|
310 from the original file to the copy, Mercurial prevents this
|
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bos@559
|
311 class of problem. To my knowledge, Mercurial is the
|
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bos@559
|
312 <emphasis>only</emphasis> revision control system that
|
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bos@559
|
313 propagates changes across copies like this.</para>
|
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bos@559
|
314
|
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bos@584
|
315 <para id="x_1ca">Once your change history has a record that the copy and
|
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bos@559
|
316 subsequent merge occurred, there's usually no further need to
|
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bos@559
|
317 propagate changes from the original file to the copied file,
|
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bos@559
|
318 and that's why Mercurial only propagates changes across copies
|
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bos@674
|
319 at the first merge, and not afterwards.</para>
|
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bos@674
|
320 </sect2>
|
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bos@674
|
321
|
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bos@559
|
322 <sect2>
|
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bos@559
|
323 <title>How to make changes <emphasis>not</emphasis> follow a
|
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bos@559
|
324 copy</title>
|
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bos@559
|
325
|
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bos@584
|
326 <para id="x_1cb">If, for some reason, you decide that this business of
|
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bos@559
|
327 automatically propagating changes across copies is not for
|
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bos@559
|
328 you, simply use your system's normal file copy command (on
|
|
bos@559
|
329 Unix-like systems, that's <command>cp</command>) to make a
|
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bos@559
|
330 copy of a file, then <command role="hg-cmd">hg add</command>
|
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bos@559
|
331 the new copy by hand. Before you do so, though, please do
|
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bos@592
|
332 reread <xref linkend="sec:daily:why-copy"/>, and make
|
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bos@559
|
333 an informed
|
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bos@672
|
334 decision that this behavior is not appropriate to your
|
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bos@559
|
335 specific case.</para>
|
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bos@559
|
336
|
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bos@559
|
337 </sect2>
|
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bos@559
|
338 <sect2>
|
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bos@674
|
339 <title>Behavior of the <command role="hg-cmd">hg copy</command>
|
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bos@559
|
340 command</title>
|
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bos@559
|
341
|
|
bos@584
|
342 <para id="x_1cc">When you use the <command role="hg-cmd">hg copy</command>
|
|
bos@559
|
343 command, Mercurial makes a copy of each source file as it
|
|
bos@559
|
344 currently stands in the working directory. This means that if
|
|
bos@559
|
345 you make some modifications to a file, then <command
|
|
bos@559
|
346 role="hg-cmd">hg copy</command> it without first having
|
|
bos@559
|
347 committed those changes, the new copy will also contain the
|
|
bos@559
|
348 modifications you have made up until that point. (I find this
|
|
bos@672
|
349 behavior a little counterintuitive, which is why I mention it
|
|
bos@559
|
350 here.)</para>
|
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bos@559
|
351
|
|
bos@674
|
352 <para id="x_1cd">The <command role="hg-cmd">hg copy</command>
|
|
bos@674
|
353 command acts similarly to the Unix <command>cp</command>
|
|
bos@674
|
354 command (you can use the <command role="hg-cmd">hg
|
|
bos@674
|
355 cp</command> alias if you prefer). We must supply two or
|
|
bos@674
|
356 more arguments, of which the last is treated as the
|
|
bos@674
|
357 <emphasis>destination</emphasis>, and all others are
|
|
bos@674
|
358 <emphasis>sources</emphasis>.</para>
|
|
bos@674
|
359
|
|
bos@676
|
360 <para id="x_685">If you pass <command role="hg-cmd">hg copy</command> a
|
|
bos@674
|
361 single file as the source, and the destination does not exist,
|
|
bos@674
|
362 it creates a new file with that name.</para>
|
|
bos@567
|
363
|
|
bos@567
|
364 &interaction.daily.copy.simple;
|
|
bos@567
|
365
|
|
bos@584
|
366 <para id="x_1ce">If the destination is a directory, Mercurial copies its
|
|
bos@567
|
367 sources into that directory.</para>
|
|
bos@567
|
368
|
|
bos@567
|
369 &interaction.daily.copy.dir-dest;
|
|
bos@567
|
370
|
|
bos@584
|
371 <para id="x_1cf">Copying a directory is
|
|
bos@559
|
372 recursive, and preserves the directory structure of the
|
|
bos@567
|
373 source.</para>
|
|
bos@567
|
374
|
|
bos@567
|
375 &interaction.daily.copy.dir-src;
|
|
bos@567
|
376
|
|
bos@584
|
377 <para id="x_1d0">If the source and destination are both directories, the
|
|
bos@567
|
378 source tree is recreated in the destination directory.</para>
|
|
bos@567
|
379
|
|
bos@567
|
380 &interaction.daily.copy.dir-src-dest;
|
|
bos@559
|
381
|
|
bos@674
|
382 <para id="x_1d1">As with the <command role="hg-cmd">hg remove</command>
|
|
bos@559
|
383 command, if you copy a file manually and then want Mercurial
|
|
bos@559
|
384 to know that you've copied the file, simply use the <option
|
|
bos@559
|
385 role="hg-opt-copy">--after</option> option to <command
|
|
bos@567
|
386 role="hg-cmd">hg copy</command>.</para>
|
|
bos@567
|
387
|
|
bos@567
|
388 &interaction.daily.copy.after;
|
|
bos@559
|
389 </sect2>
|
|
bos@559
|
390 </sect1>
|
|
bos@674
|
391
|
|
bos@559
|
392 <sect1>
|
|
bos@559
|
393 <title>Renaming files</title>
|
|
bos@559
|
394
|
|
bos@584
|
395 <para id="x_1d2">It's rather more common to need to rename a file than to
|
|
bos@559
|
396 make a copy of it. The reason I discussed the <command
|
|
bos@559
|
397 role="hg-cmd">hg copy</command> command before talking about
|
|
bos@559
|
398 renaming files is that Mercurial treats a rename in essentially
|
|
bos@559
|
399 the same way as a copy. Therefore, knowing what Mercurial does
|
|
bos@559
|
400 when you copy a file tells you what to expect when you rename a
|
|
bos@559
|
401 file.</para>
|
|
bos@559
|
402
|
|
bos@584
|
403 <para id="x_1d3">When you use the <command role="hg-cmd">hg rename</command>
|
|
bos@559
|
404 command, Mercurial makes a copy of each source file, then
|
|
bos@567
|
405 deletes it and marks the file as removed.</para>
|
|
bos@567
|
406
|
|
bos@567
|
407 &interaction.daily.rename.rename;
|
|
bos@567
|
408
|
|
bos@584
|
409 <para id="x_1d4">The <command role="hg-cmd">hg status</command> command shows
|
|
bos@567
|
410 the newly copied file as added, and the copied-from file as
|
|
bos@567
|
411 removed.</para>
|
|
bos@567
|
412
|
|
bos@567
|
413 &interaction.daily.rename.status;
|
|
bos@567
|
414
|
|
bos@584
|
415 <para id="x_1d5">As with the results of a <command role="hg-cmd">hg
|
|
bos@567
|
416 copy</command>, we must use the <option
|
|
bos@567
|
417 role="hg-opt-status">-C</option> option to <command
|
|
bos@559
|
418 role="hg-cmd">hg status</command> to see that the added file
|
|
bos@559
|
419 is really being tracked by Mercurial as a copy of the original,
|
|
bos@567
|
420 now removed, file.</para>
|
|
bos@567
|
421
|
|
bos@567
|
422 &interaction.daily.rename.status-copy;
|
|
bos@559
|
423
|
|
bos@584
|
424 <para id="x_1d6">As with <command role="hg-cmd">hg remove</command> and
|
|
bos@559
|
425 <command role="hg-cmd">hg copy</command>, you can tell Mercurial
|
|
bos@559
|
426 about a rename after the fact using the <option
|
|
bos@559
|
427 role="hg-opt-rename">--after</option> option. In most other
|
|
bos@672
|
428 respects, the behavior of the <command role="hg-cmd">hg
|
|
bos@559
|
429 rename</command> command, and the options it accepts, are
|
|
bos@559
|
430 similar to the <command role="hg-cmd">hg copy</command>
|
|
bos@559
|
431 command.</para>
|
|
bos@559
|
432
|
|
bos@676
|
433 <para id="x_686">If you're familiar with the Unix command line, you'll be
|
|
bos@674
|
434 glad to know that <command role="hg-cmd">hg rename</command>
|
|
bos@674
|
435 command can be invoked as <command role="hg-cmd">hg
|
|
bos@674
|
436 mv</command>.</para>
|
|
bos@674
|
437
|
|
bos@559
|
438 <sect2>
|
|
bos@559
|
439 <title>Renaming files and merging changes</title>
|
|
bos@559
|
440
|
|
bos@584
|
441 <para id="x_1d7">Since Mercurial's rename is implemented as
|
|
bos@559
|
442 copy-and-remove, the same propagation of changes happens when
|
|
bos@559
|
443 you merge after a rename as after a copy.</para>
|
|
bos@559
|
444
|
|
bos@584
|
445 <para id="x_1d8">If I modify a file, and you rename it to a new name, and
|
|
bos@559
|
446 then we merge our respective changes, my modifications to the
|
|
bos@559
|
447 file under its original name will be propagated into the file
|
|
bos@559
|
448 under its new name. (This is something you might expect to
|
|
bos@559
|
449 <quote>simply work,</quote> but not all revision control
|
|
bos@559
|
450 systems actually do this.)</para>
|
|
bos@559
|
451
|
|
bos@584
|
452 <para id="x_1d9">Whereas having changes follow a copy is a feature where
|
|
bos@559
|
453 you can perhaps nod and say <quote>yes, that might be
|
|
bos@559
|
454 useful,</quote> it should be clear that having them follow a
|
|
bos@559
|
455 rename is definitely important. Without this facility, it
|
|
bos@559
|
456 would simply be too easy for changes to become orphaned when
|
|
bos@559
|
457 files are renamed.</para>
|
|
bos@674
|
458 </sect2>
|
|
bos@674
|
459
|
|
bos@559
|
460 <sect2>
|
|
bos@559
|
461 <title>Divergent renames and merging</title>
|
|
bos@559
|
462
|
|
bos@584
|
463 <para id="x_1da">The case of diverging names occurs when two developers
|
|
bos@559
|
464 start with a file&emdash;let's call it
|
|
bos@559
|
465 <filename>foo</filename>&emdash;in their respective
|
|
bos@559
|
466 repositories.</para>
|
|
bos@559
|
467
|
|
bos@567
|
468 &interaction.rename.divergent.clone;
|
|
bos@567
|
469
|
|
bos@584
|
470 <para id="x_1db">Anne renames the file to <filename>bar</filename>.</para>
|
|
bos@567
|
471
|
|
bos@567
|
472 &interaction.rename.divergent.rename.anne;
|
|
bos@567
|
473
|
|
bos@584
|
474 <para id="x_1dc">Meanwhile, Bob renames it to
|
|
bos@674
|
475 <filename>quux</filename>. (Remember that <command
|
|
bos@674
|
476 role="hg-cmd">hg mv</command> is an alias for <command
|
|
bos@674
|
477 role="hg-cmd">hg rename</command>.)</para>
|
|
bos@567
|
478
|
|
bos@567
|
479 &interaction.rename.divergent.rename.bob;
|
|
bos@559
|
480
|
|
bos@584
|
481 <para id="x_1dd">I like to think of this as a conflict because each
|
|
bos@559
|
482 developer has expressed different intentions about what the
|
|
bos@559
|
483 file ought to be named.</para>
|
|
bos@559
|
484
|
|
bos@584
|
485 <para id="x_1de">What do you think should happen when they merge their
|
|
bos@672
|
486 work? Mercurial's actual behavior is that it always preserves
|
|
bos@559
|
487 <emphasis>both</emphasis> names when it merges changesets that
|
|
bos@567
|
488 contain divergent renames.</para>
|
|
bos@567
|
489
|
|
bos@567
|
490 &interaction.rename.divergent.merge;
|
|
bos@559
|
491
|
|
bos@674
|
492 <para id="x_1df">Notice that while Mercurial warns about the divergent
|
|
bos@674
|
493 renames, it leaves it up to you to do something about the
|
|
bos@559
|
494 divergence after the merge.</para>
|
|
bos@674
|
495 </sect2>
|
|
bos@674
|
496
|
|
bos@559
|
497 <sect2>
|
|
bos@559
|
498 <title>Convergent renames and merging</title>
|
|
bos@559
|
499
|
|
bos@584
|
500 <para id="x_1e0">Another kind of rename conflict occurs when two people
|
|
bos@559
|
501 choose to rename different <emphasis>source</emphasis> files
|
|
bos@559
|
502 to the same <emphasis>destination</emphasis>. In this case,
|
|
bos@559
|
503 Mercurial runs its normal merge machinery, and lets you guide
|
|
bos@559
|
504 it to a suitable resolution.</para>
|
|
bos@674
|
505 </sect2>
|
|
bos@674
|
506
|
|
bos@559
|
507 <sect2>
|
|
bos@559
|
508 <title>Other name-related corner cases</title>
|
|
bos@559
|
509
|
|
bos@584
|
510 <para id="x_1e1">Mercurial has a longstanding bug in which it fails to
|
|
bos@559
|
511 handle a merge where one side has a file with a given name,
|
|
bos@559
|
512 while another has a directory with the same name. This is
|
|
bos@559
|
513 documented as <ulink role="hg-bug"
|
|
bos@559
|
514 url="http://www.selenic.com/mercurial/bts/issue29">issue
|
|
bos@567
|
515 29</ulink>.</para>
|
|
bos@567
|
516
|
|
bos@567
|
517 &interaction.issue29.go;
|
|
bos@559
|
518
|
|
bos@559
|
519 </sect2>
|
|
bos@559
|
520 </sect1>
|
|
bos@674
|
521
|
|
bos@559
|
522 <sect1>
|
|
bos@559
|
523 <title>Recovering from mistakes</title>
|
|
bos@559
|
524
|
|
bos@584
|
525 <para id="x_1e2">Mercurial has some useful commands that will help you to
|
|
bos@559
|
526 recover from some common mistakes.</para>
|
|
bos@559
|
527
|
|
bos@584
|
528 <para id="x_1e3">The <command role="hg-cmd">hg revert</command> command lets
|
|
bos@559
|
529 you undo changes that you have made to your working directory.
|
|
bos@559
|
530 For example, if you <command role="hg-cmd">hg add</command> a
|
|
bos@559
|
531 file by accident, just run <command role="hg-cmd">hg
|
|
bos@559
|
532 revert</command> with the name of the file you added, and
|
|
bos@559
|
533 while the file won't be touched in any way, it won't be tracked
|
|
bos@559
|
534 for adding by Mercurial any longer, either. You can also use
|
|
bos@559
|
535 <command role="hg-cmd">hg revert</command> to get rid of
|
|
bos@559
|
536 erroneous changes to a file.</para>
|
|
bos@559
|
537
|
|
bos@674
|
538 <para id="x_1e4">It's good to remember that the <command role="hg-cmd">hg
|
|
bos@559
|
539 revert</command> command is useful for changes that you have
|
|
bos@559
|
540 not yet committed. Once you've committed a change, if you
|
|
bos@559
|
541 decide it was a mistake, you can still do something about it,
|
|
bos@559
|
542 though your options may be more limited.</para>
|
|
bos@559
|
543
|
|
bos@592
|
544 <para id="x_1e5">For more information about the <command
|
|
bos@592
|
545 role="hg-cmd">hg revert</command> command, and details about
|
|
bos@592
|
546 how to deal with changes you have already committed, see <xref
|
|
bos@559
|
547 linkend="chap:undo"/>.</para>
|
|
bos@674
|
548 </sect1>
|
|
bos@674
|
549
|
|
bos@674
|
550 <sect1>
|
|
bos@674
|
551 <title>Dealing with tricky merges</title>
|
|
bos@674
|
552
|
|
bos@676
|
553 <para id="x_687">In a complicated or large project, it's not unusual for a
|
|
bos@674
|
554 merge of two changesets to result in some headaches. Suppose
|
|
bos@674
|
555 there's a big source file that's been extensively edited by each
|
|
bos@674
|
556 side of a merge: this is almost inevitably going to result in
|
|
bos@674
|
557 conflicts, some of which can take a few tries to sort
|
|
bos@674
|
558 out.</para>
|
|
bos@674
|
559
|
|
bos@676
|
560 <para id="x_688">Let's develop a simple case of this and see how to deal with
|
|
bos@674
|
561 it. We'll start off with a repository containing one file, and
|
|
bos@674
|
562 clone it twice.</para>
|
|
bos@674
|
563
|
|
bos@674
|
564 &interaction.ch04-resolve.init;
|
|
bos@674
|
565
|
|
bos@676
|
566 <para id="x_689">In one clone, we'll modify the file in one way.</para>
|
|
bos@674
|
567
|
|
bos@674
|
568 &interaction.ch04-resolve.left;
|
|
bos@674
|
569
|
|
bos@676
|
570 <para id="x_68a">In another, we'll modify the file differently.</para>
|
|
bos@674
|
571
|
|
bos@674
|
572 &interaction.ch04-resolve.right;
|
|
bos@674
|
573
|
|
bos@676
|
574 <para id="x_68b">Next, we'll pull each set of changes into our original
|
|
bos@674
|
575 repo.</para>
|
|
bos@674
|
576
|
|
bos@674
|
577 &interaction.ch04-resolve.pull;
|
|
bos@674
|
578
|
|
bos@676
|
579 <para id="x_68c">We expect our repository to now contain two heads.</para>
|
|
bos@674
|
580
|
|
bos@674
|
581 &interaction.ch04-resolve.heads;
|
|
bos@674
|
582
|
|
bos@676
|
583 <para id="x_68d">Normally, if we run <command role="hg-cmd">hg
|
|
bos@674
|
584 merge</command> at this point, it will drop us into a GUI that
|
|
bos@674
|
585 will let us manually resolve the conflicting edits to
|
|
bos@674
|
586 <filename>myfile.txt</filename>. However, to simplify things
|
|
bos@674
|
587 for presentation here, we'd like the merge to fail immediately
|
|
bos@674
|
588 instead. Here's one way we can do so.</para>
|
|
bos@674
|
589
|
|
bos@674
|
590 &interaction.ch04-resolve.export;
|
|
bos@674
|
591
|
|
bos@676
|
592 <para id="x_68e">We've told Mercurial's merge machinery to run the command
|
|
bos@674
|
593 <command>false</command> (which, as we desire, fails
|
|
bos@674
|
594 immediately) if it detects a merge that it can't sort out
|
|
bos@674
|
595 automatically.</para>
|
|
bos@674
|
596
|
|
bos@676
|
597 <para id="x_68f">If we now fire up <command role="hg-cmd">hg
|
|
bos@674
|
598 merge</command>, it should grind to a halt and report a
|
|
bos@674
|
599 failure.</para>
|
|
bos@674
|
600
|
|
bos@674
|
601 &interaction.ch04-resolve.merge;
|
|
bos@674
|
602
|
|
bos@676
|
603 <para id="x_690">Even if we don't notice that the merge failed, Mercurial
|
|
bos@674
|
604 will prevent us from accidentally committing the result of a
|
|
bos@674
|
605 failed merge.</para>
|
|
bos@674
|
606
|
|
bos@674
|
607 &interaction.ch04-resolve.cifail;
|
|
bos@674
|
608
|
|
bos@676
|
609 <para id="x_691">When <command role="hg-cmd">hg commit</command> fails in
|
|
bos@674
|
610 this case, it suggests that we use the unfamiliar <command
|
|
bos@674
|
611 role="hg-cmd">hg resolve</command> command. As usual,
|
|
bos@674
|
612 <command role="hg-cmd">hg help resolve</command> will print a
|
|
bos@674
|
613 helpful synopsis.</para>
|
|
bos@674
|
614
|
|
bos@674
|
615 <sect2>
|
|
bos@674
|
616 <title>File resolution states</title>
|
|
bos@674
|
617
|
|
bos@676
|
618 <para id="x_692">When a merge occurs, most files will usually remain
|
|
bos@674
|
619 unmodified. For each file where Mercurial has to do
|
|
bos@674
|
620 something, it tracks the state of the file.</para>
|
|
bos@674
|
621
|
|
bos@674
|
622 <itemizedlist>
|
|
bos@674
|
623 <listitem>
|
|
bos@676
|
624 <para id="x_693">A <emphasis>resolved</emphasis> file has been
|
|
bos@674
|
625 successfully merged, either automatically by Mercurial or
|
|
bos@674
|
626 manually with human intervention.</para>
|
|
bos@674
|
627 </listitem>
|
|
bos@674
|
628 <listitem>
|
|
bos@676
|
629 <para id="x_694">An <emphasis>unresolved</emphasis> file was not merged
|
|
bos@674
|
630 successfully, and needs more attention.</para>
|
|
bos@674
|
631 </listitem>
|
|
bos@674
|
632 </itemizedlist>
|
|
bos@674
|
633
|
|
bos@676
|
634 <para id="x_695">If Mercurial sees <emphasis>any</emphasis> file in the
|
|
bos@674
|
635 unresolved state after a merge, it considers the merge to have
|
|
bos@674
|
636 failed. Fortunately, we do not need to restart the entire
|
|
bos@674
|
637 merge from scratch.</para>
|
|
bos@674
|
638
|
|
bos@676
|
639 <para id="x_696">The <option role="hg-opt-resolve">--list</option> or
|
|
bos@674
|
640 <option role="hg-opt-resolve">-l</option> option to <command
|
|
bos@674
|
641 role="hg-cmd">hg resolve</command> prints out the state of
|
|
bos@674
|
642 each merged file.</para>
|
|
bos@674
|
643
|
|
bos@674
|
644 &interaction.ch04-resolve.list;
|
|
bos@674
|
645
|
|
bos@676
|
646 <para id="x_697">In the output from <command role="hg-cmd">hg
|
|
bos@674
|
647 resolve</command>, a resolved file is marked with
|
|
bos@674
|
648 <literal>R</literal>, while an unresolved file is marked with
|
|
bos@674
|
649 <literal>U</literal>. If any files are listed with
|
|
bos@674
|
650 <literal>U</literal>, we know that an attempt to commit the
|
|
bos@674
|
651 results of the merge will fail.</para>
|
|
bos@674
|
652 </sect2>
|
|
bos@674
|
653
|
|
bos@674
|
654 <sect2>
|
|
bos@674
|
655 <title>Resolving a file merge</title>
|
|
bos@674
|
656
|
|
bos@676
|
657 <para id="x_698">We have several options to move a file from the unresolved
|
|
bos@674
|
658 into the resolved state. By far the most common is to rerun
|
|
bos@674
|
659 <command role="hg-cmd">hg resolve</command>. If we pass the
|
|
bos@674
|
660 names of individual files or directories, it will retry the
|
|
bos@674
|
661 merges of any unresolved files present in those locations. We
|
|
bos@674
|
662 can also pass the <option role="hg-opt-resolve">--all</option>
|
|
bos@674
|
663 or <option role="hg-opt-resolve">-a</option> option, which
|
|
bos@674
|
664 will retry the merges of <emphasis>all</emphasis> unresolved
|
|
bos@674
|
665 files.</para>
|
|
bos@674
|
666
|
|
bos@676
|
667 <para id="x_699">Mercurial also lets us modify the resolution state of a
|
|
bos@674
|
668 file directly. We can manually mark a file as resolved using
|
|
bos@674
|
669 the <option role="hg-opt-resolve">--mark</option> option, or
|
|
bos@674
|
670 as unresolved using the <option
|
|
bos@674
|
671 role="hg-opt-resolve">--unmark</option> option. This allows
|
|
bos@674
|
672 us to clean up a particularly messy merge by hand, and to keep
|
|
bos@674
|
673 track of our progress with each file as we go.</para>
|
|
bos@674
|
674 </sect2>
|
|
bos@559
|
675 </sect1>
|
|
bos@683
|
676
|
|
bos@683
|
677 <sect1>
|
|
bos@683
|
678 <title>More useful diffs</title>
|
|
bos@683
|
679
|
|
bos@684
|
680 <para id="x_6c7">The default output of the <command role="hg-cmd">hg
|
|
bos@683
|
681 diff</command> command is backwards compatible with the
|
|
bos@683
|
682 regular <command>diff</command> command, but this has some
|
|
bos@683
|
683 drawbacks.</para>
|
|
bos@683
|
684
|
|
bos@684
|
685 <para id="x_6c8">Consider the case where we use <command role="hg-cmd">hg
|
|
bos@683
|
686 rename</command> to rename a file.</para>
|
|
bos@683
|
687
|
|
bos@683
|
688 &interaction.ch04-diff.rename.basic;
|
|
bos@683
|
689
|
|
bos@684
|
690 <para id="x_6c9">The output of <command role="hg-cmd">hg diff</command> above
|
|
bos@683
|
691 obscures the fact that we simply renamed a file. The <command
|
|
bos@683
|
692 role="hg-cmd">hg diff</command> command accepts an option,
|
|
bos@683
|
693 <option>--git</option> or <option>-g</option>, to use a newer
|
|
bos@683
|
694 diff format that displays such information in a more readable
|
|
bos@683
|
695 form.</para>
|
|
bos@683
|
696
|
|
bos@683
|
697 &interaction.ch04-diff.rename.git;
|
|
bos@683
|
698
|
|
bos@684
|
699 <para id="x_6ca">This option also helps with a case that can otherwise be
|
|
bos@683
|
700 confusing: a file that appears to be modified according to
|
|
bos@683
|
701 <command role="hg-cmd">hg status</command>, but for which
|
|
bos@683
|
702 <command role="hg-cmd">hg diff</command> prints nothing. This
|
|
bos@683
|
703 situation can arise if we change the file's execute
|
|
bos@683
|
704 permissions.</para>
|
|
bos@683
|
705
|
|
bos@683
|
706 &interaction.ch04-diff.chmod;
|
|
bos@683
|
707
|
|
bos@684
|
708 <para id="x_6cb">The normal <command>diff</command> command pays no attention
|
|
bos@683
|
709 to file permissions, which is why <command role="hg-cmd">hg
|
|
bos@683
|
710 diff</command> prints nothing by default. If we supply it
|
|
bos@683
|
711 with the <option>-g</option> option, it tells us what really
|
|
bos@683
|
712 happened.</para>
|
|
bos@683
|
713
|
|
bos@683
|
714 &interaction.ch04-diff.chmod.git;
|
|
bos@683
|
715 </sect1>
|
|
bos@683
|
716
|
|
bos@683
|
717 <sect1>
|
|
bos@683
|
718 <title>Which files to manage, and which to avoid</title>
|
|
bos@683
|
719
|
|
bos@684
|
720 <para id="x_6cc">Revision control systems are generally best at managing text
|
|
bos@683
|
721 files that are written by humans, such as source code, where the
|
|
bos@683
|
722 files do not change much from one revision to the next. Some
|
|
bos@683
|
723 centralized revision control systems can also deal tolerably
|
|
bos@683
|
724 well with binary files, such as bitmap images.</para>
|
|
bos@683
|
725
|
|
bos@684
|
726 <para id="x_6cd">For instance, a game development team will typically manage
|
|
bos@683
|
727 both its source code and all of its binary assets (e.g. geometry
|
|
bos@683
|
728 data, textures, map layouts) in a revision control
|
|
bos@683
|
729 system.</para>
|
|
bos@683
|
730
|
|
bos@684
|
731 <para id="x_6ce">Because it is usually impossible to merge two conflicting
|
|
bos@683
|
732 modifications to a binary file, centralized systems often
|
|
bos@683
|
733 provide a file locking mechanism that allow a user to say
|
|
bos@683
|
734 <quote>I am the only person who can edit this
|
|
bos@683
|
735 file</quote>.</para>
|
|
bos@683
|
736
|
|
bos@684
|
737 <para id="x_6cf">Compared to a centralized system, a distributed revision
|
|
bos@683
|
738 control system changes some of the factors that guide decisions
|
|
bos@683
|
739 over which files to manage and how.</para>
|
|
bos@683
|
740
|
|
bos@684
|
741 <para id="x_6d0">For instance, a distributed revision control system cannot,
|
|
bos@683
|
742 by its nature, offer a file locking facility. There is thus no
|
|
bos@683
|
743 built-in mechanism to prevent two people from making conflicting
|
|
bos@683
|
744 changes to a binary file. If you have a team where several
|
|
bos@683
|
745 people may be editing binary files frequently, it may not be a
|
|
bos@683
|
746 good idea to use Mercurial&emdash;or any other distributed
|
|
bos@683
|
747 revision control system&emdash;to manage those files.</para>
|
|
bos@683
|
748
|
|
bos@684
|
749 <para id="x_6d1">When storing modifications to a file, Mercurial usually
|
|
bos@683
|
750 saves only the differences between the previous and current
|
|
bos@683
|
751 versions of the file. For most text files, this is extremely
|
|
bos@683
|
752 efficient. However, some files (particularly binary files) are
|
|
bos@683
|
753 laid out in such a way that even a small change to a file's
|
|
bos@683
|
754 logical content results in many or most of the bytes inside the
|
|
bos@683
|
755 file changing. For instance, compressed files are particularly
|
|
bos@683
|
756 susceptible to this. If the differences between each successive
|
|
bos@683
|
757 version of a file are always large, Mercurial will not be able
|
|
bos@683
|
758 to store the file's revision history very efficiently. This can
|
|
bos@683
|
759 affect both local storage needs and the amount of time it takes
|
|
bos@683
|
760 to clone a repository.</para>
|
|
bos@683
|
761
|
|
bos@684
|
762 <para id="x_6d2">To get an idea of how this could affect you in practice,
|
|
bos@683
|
763 suppose you want to use Mercurial to manage an OpenOffice
|
|
bos@683
|
764 document. OpenOffice stores documents on disk as compressed zip
|
|
bos@683
|
765 files. Edit even a single letter of your document in OpenOffice,
|
|
bos@683
|
766 and almost every byte in the entire file will change when you
|
|
bos@683
|
767 save it. Now suppose that file is 2MB in size. Because most of
|
|
bos@683
|
768 the file changes every time you save, Mercurial will have to
|
|
bos@683
|
769 store all 2MB of the file every time you commit, even though
|
|
bos@683
|
770 from your perspective, perhaps only a few words are changing
|
|
bos@683
|
771 each time. A single frequently-edited file that is not friendly
|
|
bos@683
|
772 to Mercurial's storage assumptions can easily have an outsized
|
|
bos@683
|
773 effect on the size of the repository.</para>
|
|
bos@683
|
774
|
|
bos@684
|
775 <para id="x_6d3">Even worse, if both you and someone else edit the OpenOffice
|
|
bos@683
|
776 document you're working on, there is no useful way to merge your
|
|
bos@683
|
777 work. In fact, there isn't even a good way to tell what the
|
|
bos@683
|
778 differences are between your respective changes.</para>
|
|
bos@683
|
779
|
|
bos@684
|
780 <para id="x_6d4">There are thus a few clear recommendations about specific
|
|
bos@683
|
781 kinds of files to be very careful with.</para>
|
|
bos@683
|
782
|
|
bos@683
|
783 <itemizedlist>
|
|
bos@683
|
784 <listitem>
|
|
bos@684
|
785 <para id="x_6d5">Files that are very large and incompressible, e.g. ISO
|
|
bos@683
|
786 CD-ROM images, will by virtue of sheer size make clones over
|
|
bos@683
|
787 a network very slow.</para>
|
|
bos@683
|
788 </listitem>
|
|
bos@683
|
789 <listitem>
|
|
bos@684
|
790 <para id="x_6d6">Files that change a lot from one revision to the next
|
|
bos@683
|
791 may be expensive to store if you edit them frequently, and
|
|
bos@683
|
792 conflicts due to concurrent edits may be difficult to
|
|
bos@683
|
793 resolve.</para>
|
|
bos@683
|
794 </listitem>
|
|
bos@683
|
795 </itemizedlist>
|
|
bos@683
|
796 </sect1>
|
|
bos@683
|
797
|
|
bos@683
|
798 <sect1>
|
|
bos@683
|
799 <title>Backups and mirroring</title>
|
|
bos@683
|
800
|
|
bos@684
|
801 <para id="x_6d7">Since Mercurial maintains a complete copy of history in each
|
|
bos@683
|
802 clone, everyone who uses Mercurial to collaborate on a project
|
|
bos@683
|
803 can potentially act as a source of backups in the event of a
|
|
bos@683
|
804 catastrophe. If a central repository becomes unavailable, you
|
|
bos@683
|
805 can construct a replacement simply by cloning a copy of the
|
|
bos@683
|
806 repository from one contributor, and pulling any changes they
|
|
bos@683
|
807 may not have seen from others.</para>
|
|
bos@683
|
808
|
|
bos@684
|
809 <para id="x_6d8">It is simple to use Mercurial to perform off-site backups
|
|
bos@683
|
810 and remote mirrors. Set up a periodic job (e.g. via the
|
|
bos@683
|
811 <command>cron</command> command) on a remote server to pull
|
|
bos@683
|
812 changes from your master repositories every hour. This will
|
|
bos@683
|
813 only be tricky in the unlikely case that the number of master
|
|
bos@683
|
814 repositories you maintain changes frequently, in which case
|
|
bos@683
|
815 you'll need to do a little scripting to refresh the list of
|
|
bos@683
|
816 repositories to back up.</para>
|
|
bos@683
|
817
|
|
bos@684
|
818 <para id="x_6d9">If you perform traditional backups of your master
|
|
bos@683
|
819 repositories to tape or disk, and you want to back up a
|
|
bos@683
|
820 repository named <filename>myrepo</filename>. Use <command>hg
|
|
bos@683
|
821 clone -U myrepo myrepo.bak</command> to create a
|
|
bos@683
|
822 clone of <filename>myrepo</filename> before you start your
|
|
bos@683
|
823 backups. The <option>-U</option> option doesn't check out a
|
|
bos@683
|
824 working directory after the clone completes, since that would be
|
|
bos@685
|
825 superfluous and make the backup take longer.</para>
|
|
bos@683
|
826
|
|
bos@684
|
827 <para id="x_6da">If you then back up <filename>myrepo.bak</filename> instead
|
|
bos@683
|
828 of <filename>myrepo</filename>, you will be guaranteed to have a
|
|
bos@683
|
829 consistent snapshot of your repository that won't be pushed to
|
|
bos@683
|
830 by an insomniac developer in mid-backup.</para>
|
|
bos@683
|
831 </sect1>
|
|
bos@559
|
832 </chapter>
|
|
bos@559
|
833
|
|
bos@559
|
834 <!--
|
|
bos@559
|
835 local variables:
|
|
bos@559
|
836 sgml-parent-document: ("00book.xml" "book" "chapter")
|
|
bos@559
|
837 end:
|
|
bos@559
|
838 -->
|
