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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:names">
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4 <title>File names and pattern matching</title>
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5
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6 <para>Mercurial provides mechanisms that let you work with file
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7 names in a consistent and expressive way.</para>
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8
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9 <sect1>
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10 <title>Simple file naming</title>
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11
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12 <para>Mercurial uses a unified piece of machinery <quote>under the
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13 hood</quote> to handle file names. Every command behaves
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14 uniformly with respect to file names. The way in which commands
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15 work with file names is as follows.</para>
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16
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17 <para>If you explicitly name real files on the command line,
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18 Mercurial works with exactly those files, as you would expect.
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19 <!-- &interaction.filenames.files; --></para>
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20
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21 <para>When you provide a directory name, Mercurial will interpret
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22 this as <quote>operate on every file in this directory and its
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23 subdirectories</quote>. Mercurial traverses the files and
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24 subdirectories in a directory in alphabetical order. When it
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25 encounters a subdirectory, it will traverse that subdirectory
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26 before continuing with the current directory. <!--
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27 &interaction.filenames.dirs; --></para>
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28
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29 </sect1>
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30 <sect1>
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31 <title>Running commands without any file names</title>
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32
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33 <para>Mercurial's commands that work with file names have useful
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34 default behaviours when you invoke them without providing any
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35 file names or patterns. What kind of behaviour you should
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36 expect depends on what the command does. Here are a few rules
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37 of thumb you can use to predict what a command is likely to do
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38 if you don't give it any names to work with.</para>
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39 <itemizedlist>
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40 <listitem><para>Most commands will operate on the entire working
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41 directory. This is what the <command role="hg-cmd">hg
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42 add</command> command does, for example.</para>
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43 </listitem>
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44 <listitem><para>If the command has effects that are difficult or
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45 impossible to reverse, it will force you to explicitly
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46 provide at least one name or pattern (see below). This
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47 protects you from accidentally deleting files by running
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48 <command role="hg-cmd">hg remove</command> with no
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49 arguments, for example.</para>
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50 </listitem></itemizedlist>
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51
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52 <para>It's easy to work around these default behaviours if they
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53 don't suit you. If a command normally operates on the whole
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54 working directory, you can invoke it on just the current
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55 directory and its subdirectories by giving it the name
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56 <quote><filename class="directory">.</filename></quote>. <!--
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57 &interaction.filenames.wdir-subdir; --></para>
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58
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59 <para>Along the same lines, some commands normally print file
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60 names relative to the root of the repository, even if you're
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61 invoking them from a subdirectory. Such a command will print
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62 file names relative to your subdirectory if you give it explicit
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63 names. Here, we're going to run <command role="hg-cmd">hg
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64 status</command> from a subdirectory, and get it to operate on
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65 the entire working directory while printing file names relative
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66 to our subdirectory, by passing it the output of the <command
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67 role="hg-cmd">hg root</command> command. <!--
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68 &interaction.filenames.wdir-relname; --></para>
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69
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70 </sect1>
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71 <sect1>
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72 <title>Telling you what's going on</title>
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73
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74 <para>The <command role="hg-cmd">hg add</command> example in the
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75 preceding section illustrates something else that's helpful
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76 about Mercurial commands. If a command operates on a file that
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77 you didn't name explicitly on the command line, it will usually
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78 print the name of the file, so that you will not be surprised
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79 what's going on.</para>
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80
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81 <para>The principle here is of <emphasis>least
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82 surprise</emphasis>. If you've exactly named a file on the
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83 command line, there's no point in repeating it back at you. If
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84 Mercurial is acting on a file <emphasis>implicitly</emphasis>,
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85 because you provided no names, or a directory, or a pattern (see
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86 below), it's safest to tell you what it's doing.</para>
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87
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88 <para>For commands that behave this way, you can silence them
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89 using the <option role="hg-opt-global">-q</option> option. You
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90 can also get them to print the name of every file, even those
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91 you've named explicitly, using the <option
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92 role="hg-opt-global">-v</option> option.</para>
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93
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94 </sect1>
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95 <sect1>
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96 <title>Using patterns to identify files</title>
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97
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98 <para>In addition to working with file and directory names,
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99 Mercurial lets you use <emphasis>patterns</emphasis> to identify
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100 files. Mercurial's pattern handling is expressive.</para>
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101
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102 <para>On Unix-like systems (Linux, MacOS, etc.), the job of
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103 matching file names to patterns normally falls to the shell. On
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104 these systems, you must explicitly tell Mercurial that a name is
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105 a pattern. On Windows, the shell does not expand patterns, so
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106 Mercurial will automatically identify names that are patterns,
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107 and expand them for you.</para>
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108
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109 <para>To provide a pattern in place of a regular name on the
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110 command line, the mechanism is simple:</para>
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111 <programlisting>syntax:patternbody</programlisting>
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112 <para>That is, a pattern is identified by a short text string that
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113 says what kind of pattern this is, followed by a colon, followed
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114 by the actual pattern.</para>
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115
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116 <para>Mercurial supports two kinds of pattern syntax. The most
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117 frequently used is called <literal>glob</literal>; this is the
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118 same kind of pattern matching used by the Unix shell, and should
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119 be familiar to Windows command prompt users, too.</para>
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120
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121 <para>When Mercurial does automatic pattern matching on Windows,
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122 it uses <literal>glob</literal> syntax. You can thus omit the
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123 <quote><literal>glob:</literal></quote> prefix on Windows, but
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124 it's safe to use it, too.</para>
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125
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126 <para>The <literal>re</literal> syntax is more powerful; it lets
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127 you specify patterns using regular expressions, also known as
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128 regexps.</para>
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129
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130 <para>By the way, in the examples that follow, notice that I'm
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131 careful to wrap all of my patterns in quote characters, so that
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132 they won't get expanded by the shell before Mercurial sees
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133 them.</para>
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134
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135 <sect2>
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136 <title>Shell-style <literal>glob</literal> patterns</title>
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137
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138 <para>This is an overview of the kinds of patterns you can use
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139 when you're matching on glob patterns.</para>
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140
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141 <para>The <quote><literal>*</literal></quote> character matches
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142 any string, within a single directory. <!--
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143 &interaction.filenames.glob.star; --></para>
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144
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145 <para>The <quote><literal>**</literal></quote> pattern matches
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146 any string, and crosses directory boundaries. It's not a
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147 standard Unix glob token, but it's accepted by several popular
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148 Unix shells, and is very useful. <!--
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149 &interaction.filenames.glob.starstar; --></para>
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150
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151 <para>The <quote><literal>?</literal></quote> pattern matches
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152 any single character. <!--
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153 &interaction.filenames.glob.question; --></para>
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154
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155 <para>The <quote><literal>[</literal></quote> character begins a
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156 <emphasis>character class</emphasis>. This matches any single
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157 character within the class. The class ends with a
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158 <quote><literal>]</literal></quote> character. A class may
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159 contain multiple <emphasis>range</emphasis>s of the form
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160 <quote><literal>a-f</literal></quote>, which is shorthand for
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161 <quote><literal>abcdef</literal></quote>. <!--
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162 &interaction.filenames.glob.range; --> If the first character
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163 after the <quote><literal>[</literal></quote> in a character
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164 class is a <quote><literal>!</literal></quote>, it
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165 <emphasis>negates</emphasis> the class, making it match any
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166 single character not in the class.</para>
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167
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168 <para>A <quote><literal>{</literal></quote> begins a group of
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169 subpatterns, where the whole group matches if any subpattern
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170 in the group matches. The <quote><literal>,</literal></quote>
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171 character separates subpatterns, and <quote><literal>}</literal></quote>
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172 ends the group. <!-- &interaction.filenames.glob.group;
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173 --></para>
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174
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175 <sect3>
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176 <title>Watch out!</title>
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177
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178 <para>Don't forget that if you want to match a pattern in any
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179 directory, you should not be using the
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180 <quote><literal>*</literal></quote> match-any token, as this
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181 will only match within one directory. Instead, use the
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182 <quote><literal>**</literal></quote> token. This small
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183 example illustrates the difference between the two. <!--
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184 &interaction.filenames.glob.star-starstar; --></para>
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185
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186 </sect3>
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187 </sect2>
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188 <sect2>
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189 <title>Regular expression matching with <literal>re</literal>
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190 patterns</title>
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191
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192 <para>Mercurial accepts the same regular expression syntax as
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193 the Python programming language (it uses Python's regexp
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194 engine internally). This is based on the Perl language's
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195 regexp syntax, which is the most popular dialect in use (it's
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196 also used in Java, for example).</para>
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197
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198 <para>I won't discuss Mercurial's regexp dialect in any detail
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199 here, as regexps are not often used. Perl-style regexps are
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200 in any case already exhaustively documented on a multitude of
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201 web sites, and in many books. Instead, I will focus here on a
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202 few things you should know if you find yourself needing to use
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203 regexps with Mercurial.</para>
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204
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205 <para>A regexp is matched against an entire file name, relative
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206 to the root of the repository. In other words, even if you're
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207 already in subbdirectory <filename
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208 class="directory">foo</filename>, if you want to match files
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209 under this directory, your pattern must start with
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210 <quote><literal>foo/</literal></quote>.</para>
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211
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212 <para>One thing to note, if you're familiar with Perl-style
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213 regexps, is that Mercurial's are <emphasis>rooted</emphasis>.
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214 That is, a regexp starts matching against the beginning of a
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215 string; it doesn't look for a match anywhere within the
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216 string. To match anywhere in a string, start your pattern
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217 with <quote><literal>.*</literal></quote>.</para>
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218
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219 </sect2>
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220 </sect1>
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221 <sect1>
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222 <title>Filtering files</title>
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223
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224 <para>Not only does Mercurial give you a variety of ways to
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225 specify files; it lets you further winnow those files using
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226 <emphasis>filters</emphasis>. Commands that work with file
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227 names accept two filtering options.</para>
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228 <itemizedlist>
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229 <listitem><para><option role="hg-opt-global">-I</option>, or
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230 <option role="hg-opt-global">--include</option>, lets you
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231 specify a pattern that file names must match in order to be
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232 processed.</para>
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233 </listitem>
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234 <listitem><para><option role="hg-opt-global">-X</option>, or
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235 <option role="hg-opt-global">--exclude</option>, gives you a
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236 way to <emphasis>avoid</emphasis> processing files, if they
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237 match this pattern.</para>
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238 </listitem></itemizedlist>
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239 <para>You can provide multiple <option
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240 role="hg-opt-global">-I</option> and <option
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241 role="hg-opt-global">-X</option> options on the command line,
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242 and intermix them as you please. Mercurial interprets the
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243 patterns you provide using glob syntax by default (but you can
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244 use regexps if you need to).</para>
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245
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246 <para>You can read a <option role="hg-opt-global">-I</option>
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247 filter as <quote>process only the files that match this
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248 filter</quote>. <!-- &interaction.filenames.filter.include;
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249 --> The <option role="hg-opt-global">-X</option> filter is best
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250 read as <quote>process only the files that don't match this
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251 pattern</quote>. <!-- &interaction.filenames.filter.exclude;
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252 --></para>
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253
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254 </sect1>
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255 <sect1>
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256 <title>Ignoring unwanted files and directories</title>
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257
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258 <para>XXX.</para>
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259
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260 </sect1>
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261 <sect1 id="sec:names:case">
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262 <title>Case sensitivity</title>
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263
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264 <para>If you're working in a mixed development environment that
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265 contains both Linux (or other Unix) systems and Macs or Windows
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266 systems, you should keep in the back of your mind the knowledge
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267 that they treat the case (<quote>N</quote> versus
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268 <quote>n</quote>) of file names in incompatible ways. This is
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269 not very likely to affect you, and it's easy to deal with if it
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270 does, but it could surprise you if you don't know about
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271 it.</para>
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272
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273 <para>Operating systems and filesystems differ in the way they
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274 handle the <emphasis>case</emphasis> of characters in file and
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275 directory names. There are three common ways to handle case in
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276 names.</para>
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277 <itemizedlist>
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278 <listitem><para>Completely case insensitive. Uppercase and
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279 lowercase versions of a letter are treated as identical,
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280 both when creating a file and during subsequent accesses.
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281 This is common on older DOS-based systems.</para>
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282 </listitem>
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283 <listitem><para>Case preserving, but insensitive. When a file
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284 or directory is created, the case of its name is stored, and
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285 can be retrieved and displayed by the operating system.
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286 When an existing file is being looked up, its case is
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287 ignored. This is the standard arrangement on Windows and
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288 MacOS. The names <filename>foo</filename> and
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289 <filename>FoO</filename> identify the same file. This
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290 treatment of uppercase and lowercase letters as
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291 interchangeable is also referred to as <emphasis>case
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292 folding</emphasis>.</para>
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293 </listitem>
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294 <listitem><para>Case sensitive. The case of a name is
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295 significant at all times. The names <filename>foo</filename>
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296 and {FoO} identify different files. This is the way Linux
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297 and Unix systems normally work.</para>
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298 </listitem></itemizedlist>
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299
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300 <para>On Unix-like systems, it is possible to have any or all of
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301 the above ways of handling case in action at once. For example,
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302 if you use a USB thumb drive formatted with a FAT32 filesystem
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303 on a Linux system, Linux will handle names on that filesystem in
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304 a case preserving, but insensitive, way.</para>
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305
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306 <sect2>
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307 <title>Safe, portable repository storage</title>
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308
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309 <para>Mercurial's repository storage mechanism is <emphasis>case
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310 safe</emphasis>. It translates file names so that they can
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311 be safely stored on both case sensitive and case insensitive
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312 filesystems. This means that you can use normal file copying
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313 tools to transfer a Mercurial repository onto, for example, a
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314 USB thumb drive, and safely move that drive and repository
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315 back and forth between a Mac, a PC running Windows, and a
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316 Linux box.</para>
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317
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318 </sect2>
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319 <sect2>
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320 <title>Detecting case conflicts</title>
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321
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322 <para>When operating in the working directory, Mercurial honours
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323 the naming policy of the filesystem where the working
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324 directory is located. If the filesystem is case preserving,
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325 but insensitive, Mercurial will treat names that differ only
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326 in case as the same.</para>
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327
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328 <para>An important aspect of this approach is that it is
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329 possible to commit a changeset on a case sensitive (typically
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330 Linux or Unix) filesystem that will cause trouble for users on
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331 case insensitive (usually Windows and MacOS) users. If a
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332 Linux user commits changes to two files, one named
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333 <filename>myfile.c</filename> and the other named
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334 <filename>MyFile.C</filename>, they will be stored correctly
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335 in the repository. And in the working directories of other
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336 Linux users, they will be correctly represented as separate
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337 files.</para>
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338
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339 <para>If a Windows or Mac user pulls this change, they will not
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340 initially have a problem, because Mercurial's repository
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341 storage mechanism is case safe. However, once they try to
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342 <command role="hg-cmd">hg update</command> the working
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343 directory to that changeset, or <command role="hg-cmd">hg
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344 merge</command> with that changeset, Mercurial will spot the
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345 conflict between the two file names that the filesystem would
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346 treat as the same, and forbid the update or merge from
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347 occurring.</para>
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348
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349 </sect2>
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350 <sect2>
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351 <title>Fixing a case conflict</title>
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352
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353 <para>If you are using Windows or a Mac in a mixed environment
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354 where some of your collaborators are using Linux or Unix, and
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355 Mercurial reports a case folding conflict when you try to
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356 <command role="hg-cmd">hg update</command> or <command
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357 role="hg-cmd">hg merge</command>, the procedure to fix the
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358 problem is simple.</para>
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359
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360 <para>Just find a nearby Linux or Unix box, clone the problem
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361 repository onto it, and use Mercurial's <command
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362 role="hg-cmd">hg rename</command> command to change the
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363 names of any offending files or directories so that they will
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364 no longer cause case folding conflicts. Commit this change,
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365 <command role="hg-cmd">hg pull</command> or <command
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366 role="hg-cmd">hg push</command> it across to your Windows or
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367 MacOS system, and <command role="hg-cmd">hg update</command>
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368 to the revision with the non-conflicting names.</para>
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369
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370 <para>The changeset with case-conflicting names will remain in
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371 your project's history, and you still won't be able to
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372 <command role="hg-cmd">hg update</command> your working
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373 directory to that changeset on a Windows or MacOS system, but
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374 you can continue development unimpeded.</para>
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375
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376 <note>
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377 <para> Prior to version 0.9.3, Mercurial did not use a case
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378 safe repository storage mechanism, and did not detect case
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379 folding conflicts. If you are using an older version of
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380 Mercurial on Windows or MacOS, I strongly recommend that you
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381 upgrade.</para>
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382 </note>
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383
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384 </sect2>
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385 </sect1>
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386 </chapter>
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387
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388 <!--
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389 local variables:
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390 sgml-parent-document: ("00book.xml" "book" "chapter")
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391 end:
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392 -->
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