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annotate en/ch07-filenames.xml @ 559:b90b024729f1

WIP DocBook snapshot that all compiles. Mirabile dictu!
author Bryan O'Sullivan <bos@serpentine.com>
date Wed Feb 18 00:22:09 2009 -0800 (2009-02-18)
parents en/ch07-filenames.tex@f72b7e6cbe90
children 21c62e09b99f
rev   line source
bos@559 1 <!-- vim: set filetype=docbkxml shiftwidth=2 autoindent expandtab tw=77 : -->
bos@559 2
bos@559 3 <chapter id="chap:names">
bos@559 4 <title>File names and pattern matching</title>
bos@559 5
bos@559 6 <para>Mercurial provides mechanisms that let you work with file
bos@559 7 names in a consistent and expressive way.</para>
bos@559 8
bos@559 9 <sect1>
bos@559 10 <title>Simple file naming</title>
bos@559 11
bos@559 12 <para>Mercurial uses a unified piece of machinery <quote>under the
bos@559 13 hood</quote> to handle file names. Every command behaves
bos@559 14 uniformly with respect to file names. The way in which commands
bos@559 15 work with file names is as follows.</para>
bos@559 16
bos@559 17 <para>If you explicitly name real files on the command line,
bos@559 18 Mercurial works with exactly those files, as you would expect.
bos@559 19 <!-- &interaction.filenames.files; --></para>
bos@559 20
bos@559 21 <para>When you provide a directory name, Mercurial will interpret
bos@559 22 this as <quote>operate on every file in this directory and its
bos@559 23 subdirectories</quote>. Mercurial traverses the files and
bos@559 24 subdirectories in a directory in alphabetical order. When it
bos@559 25 encounters a subdirectory, it will traverse that subdirectory
bos@559 26 before continuing with the current directory. <!--
bos@559 27 &interaction.filenames.dirs; --></para>
bos@559 28
bos@559 29 </sect1>
bos@559 30 <sect1>
bos@559 31 <title>Running commands without any file names</title>
bos@559 32
bos@559 33 <para>Mercurial's commands that work with file names have useful
bos@559 34 default behaviours when you invoke them without providing any
bos@559 35 file names or patterns. What kind of behaviour you should
bos@559 36 expect depends on what the command does. Here are a few rules
bos@559 37 of thumb you can use to predict what a command is likely to do
bos@559 38 if you don't give it any names to work with.</para>
bos@559 39 <itemizedlist>
bos@559 40 <listitem><para>Most commands will operate on the entire working
bos@559 41 directory. This is what the <command role="hg-cmd">hg
bos@559 42 add</command> command does, for example.</para>
bos@559 43 </listitem>
bos@559 44 <listitem><para>If the command has effects that are difficult or
bos@559 45 impossible to reverse, it will force you to explicitly
bos@559 46 provide at least one name or pattern (see below). This
bos@559 47 protects you from accidentally deleting files by running
bos@559 48 <command role="hg-cmd">hg remove</command> with no
bos@559 49 arguments, for example.</para>
bos@559 50 </listitem></itemizedlist>
bos@559 51
bos@559 52 <para>It's easy to work around these default behaviours if they
bos@559 53 don't suit you. If a command normally operates on the whole
bos@559 54 working directory, you can invoke it on just the current
bos@559 55 directory and its subdirectories by giving it the name
bos@559 56 <quote><filename class="directory">.</filename></quote>. <!--
bos@559 57 &interaction.filenames.wdir-subdir; --></para>
bos@559 58
bos@559 59 <para>Along the same lines, some commands normally print file
bos@559 60 names relative to the root of the repository, even if you're
bos@559 61 invoking them from a subdirectory. Such a command will print
bos@559 62 file names relative to your subdirectory if you give it explicit
bos@559 63 names. Here, we're going to run <command role="hg-cmd">hg
bos@559 64 status</command> from a subdirectory, and get it to operate on
bos@559 65 the entire working directory while printing file names relative
bos@559 66 to our subdirectory, by passing it the output of the <command
bos@559 67 role="hg-cmd">hg root</command> command. <!--
bos@559 68 &interaction.filenames.wdir-relname; --></para>
bos@559 69
bos@559 70 </sect1>
bos@559 71 <sect1>
bos@559 72 <title>Telling you what's going on</title>
bos@559 73
bos@559 74 <para>The <command role="hg-cmd">hg add</command> example in the
bos@559 75 preceding section illustrates something else that's helpful
bos@559 76 about Mercurial commands. If a command operates on a file that
bos@559 77 you didn't name explicitly on the command line, it will usually
bos@559 78 print the name of the file, so that you will not be surprised
bos@559 79 what's going on.</para>
bos@559 80
bos@559 81 <para>The principle here is of <emphasis>least
bos@559 82 surprise</emphasis>. If you've exactly named a file on the
bos@559 83 command line, there's no point in repeating it back at you. If
bos@559 84 Mercurial is acting on a file <emphasis>implicitly</emphasis>,
bos@559 85 because you provided no names, or a directory, or a pattern (see
bos@559 86 below), it's safest to tell you what it's doing.</para>
bos@559 87
bos@559 88 <para>For commands that behave this way, you can silence them
bos@559 89 using the <option role="hg-opt-global">-q</option> option. You
bos@559 90 can also get them to print the name of every file, even those
bos@559 91 you've named explicitly, using the <option
bos@559 92 role="hg-opt-global">-v</option> option.</para>
bos@559 93
bos@559 94 </sect1>
bos@559 95 <sect1>
bos@559 96 <title>Using patterns to identify files</title>
bos@559 97
bos@559 98 <para>In addition to working with file and directory names,
bos@559 99 Mercurial lets you use <emphasis>patterns</emphasis> to identify
bos@559 100 files. Mercurial's pattern handling is expressive.</para>
bos@559 101
bos@559 102 <para>On Unix-like systems (Linux, MacOS, etc.), the job of
bos@559 103 matching file names to patterns normally falls to the shell. On
bos@559 104 these systems, you must explicitly tell Mercurial that a name is
bos@559 105 a pattern. On Windows, the shell does not expand patterns, so
bos@559 106 Mercurial will automatically identify names that are patterns,
bos@559 107 and expand them for you.</para>
bos@559 108
bos@559 109 <para>To provide a pattern in place of a regular name on the
bos@559 110 command line, the mechanism is simple:</para>
bos@559 111 <programlisting>syntax:patternbody</programlisting>
bos@559 112 <para>That is, a pattern is identified by a short text string that
bos@559 113 says what kind of pattern this is, followed by a colon, followed
bos@559 114 by the actual pattern.</para>
bos@559 115
bos@559 116 <para>Mercurial supports two kinds of pattern syntax. The most
bos@559 117 frequently used is called <literal>glob</literal>; this is the
bos@559 118 same kind of pattern matching used by the Unix shell, and should
bos@559 119 be familiar to Windows command prompt users, too.</para>
bos@559 120
bos@559 121 <para>When Mercurial does automatic pattern matching on Windows,
bos@559 122 it uses <literal>glob</literal> syntax. You can thus omit the
bos@559 123 <quote><literal>glob:</literal></quote> prefix on Windows, but
bos@559 124 it's safe to use it, too.</para>
bos@559 125
bos@559 126 <para>The <literal>re</literal> syntax is more powerful; it lets
bos@559 127 you specify patterns using regular expressions, also known as
bos@559 128 regexps.</para>
bos@559 129
bos@559 130 <para>By the way, in the examples that follow, notice that I'm
bos@559 131 careful to wrap all of my patterns in quote characters, so that
bos@559 132 they won't get expanded by the shell before Mercurial sees
bos@559 133 them.</para>
bos@559 134
bos@559 135 <sect2>
bos@559 136 <title>Shell-style <literal>glob</literal> patterns</title>
bos@559 137
bos@559 138 <para>This is an overview of the kinds of patterns you can use
bos@559 139 when you're matching on glob patterns.</para>
bos@559 140
bos@559 141 <para>The <quote><literal>*</literal></quote> character matches
bos@559 142 any string, within a single directory. <!--
bos@559 143 &interaction.filenames.glob.star; --></para>
bos@559 144
bos@559 145 <para>The <quote><literal>**</literal></quote> pattern matches
bos@559 146 any string, and crosses directory boundaries. It's not a
bos@559 147 standard Unix glob token, but it's accepted by several popular
bos@559 148 Unix shells, and is very useful. <!--
bos@559 149 &interaction.filenames.glob.starstar; --></para>
bos@559 150
bos@559 151 <para>The <quote><literal>?</literal></quote> pattern matches
bos@559 152 any single character. <!--
bos@559 153 &interaction.filenames.glob.question; --></para>
bos@559 154
bos@559 155 <para>The <quote><literal>[</literal></quote> character begins a
bos@559 156 <emphasis>character class</emphasis>. This matches any single
bos@559 157 character within the class. The class ends with a
bos@559 158 <quote><literal>]</literal></quote> character. A class may
bos@559 159 contain multiple <emphasis>range</emphasis>s of the form
bos@559 160 <quote><literal>a-f</literal></quote>, which is shorthand for
bos@559 161 <quote><literal>abcdef</literal></quote>. <!--
bos@559 162 &interaction.filenames.glob.range; --> If the first character
bos@559 163 after the <quote><literal>[</literal></quote> in a character
bos@559 164 class is a <quote><literal>!</literal></quote>, it
bos@559 165 <emphasis>negates</emphasis> the class, making it match any
bos@559 166 single character not in the class.</para>
bos@559 167
bos@559 168 <para>A <quote><literal>{</literal></quote> begins a group of
bos@559 169 subpatterns, where the whole group matches if any subpattern
bos@559 170 in the group matches. The <quote><literal>,</literal></quote>
bos@559 171 character separates subpatterns, and <quote>\texttt{}}</quote>
bos@559 172 ends the group. <!-- &interaction.filenames.glob.group;
bos@559 173 --></para>
bos@559 174
bos@559 175 <sect3>
bos@559 176 <title>Watch out!</title>
bos@559 177
bos@559 178 <para>Don't forget that if you want to match a pattern in any
bos@559 179 directory, you should not be using the
bos@559 180 <quote><literal>*</literal></quote> match-any token, as this
bos@559 181 will only match within one directory. Instead, use the
bos@559 182 <quote><literal>**</literal></quote> token. This small
bos@559 183 example illustrates the difference between the two. <!--
bos@559 184 &interaction.filenames.glob.star-starstar; --></para>
bos@559 185
bos@559 186 </sect3>
bos@559 187 </sect2>
bos@559 188 <sect2>
bos@559 189 <title>Regular expression matching with <literal>re</literal>
bos@559 190 patterns</title>
bos@559 191
bos@559 192 <para>Mercurial accepts the same regular expression syntax as
bos@559 193 the Python programming language (it uses Python's regexp
bos@559 194 engine internally). This is based on the Perl language's
bos@559 195 regexp syntax, which is the most popular dialect in use (it's
bos@559 196 also used in Java, for example).</para>
bos@559 197
bos@559 198 <para>I won't discuss Mercurial's regexp dialect in any detail
bos@559 199 here, as regexps are not often used. Perl-style regexps are
bos@559 200 in any case already exhaustively documented on a multitude of
bos@559 201 web sites, and in many books. Instead, I will focus here on a
bos@559 202 few things you should know if you find yourself needing to use
bos@559 203 regexps with Mercurial.</para>
bos@559 204
bos@559 205 <para>A regexp is matched against an entire file name, relative
bos@559 206 to the root of the repository. In other words, even if you're
bos@559 207 already in subbdirectory <filename
bos@559 208 class="directory">foo</filename>, if you want to match files
bos@559 209 under this directory, your pattern must start with
bos@559 210 <quote><literal>foo/</literal></quote>.</para>
bos@559 211
bos@559 212 <para>One thing to note, if you're familiar with Perl-style
bos@559 213 regexps, is that Mercurial's are <emphasis>rooted</emphasis>.
bos@559 214 That is, a regexp starts matching against the beginning of a
bos@559 215 string; it doesn't look for a match anywhere within the
bos@559 216 string. To match anywhere in a string, start your pattern
bos@559 217 with <quote><literal>.*</literal></quote>.</para>
bos@559 218
bos@559 219 </sect2>
bos@559 220 </sect1>
bos@559 221 <sect1>
bos@559 222 <title>Filtering files</title>
bos@559 223
bos@559 224 <para>Not only does Mercurial give you a variety of ways to
bos@559 225 specify files; it lets you further winnow those files using
bos@559 226 <emphasis>filters</emphasis>. Commands that work with file
bos@559 227 names accept two filtering options.</para>
bos@559 228 <itemizedlist>
bos@559 229 <listitem><para><option role="hg-opt-global">-I</option>, or
bos@559 230 <option role="hg-opt-global">--include</option>, lets you
bos@559 231 specify a pattern that file names must match in order to be
bos@559 232 processed.</para>
bos@559 233 </listitem>
bos@559 234 <listitem><para><option role="hg-opt-global">-X</option>, or
bos@559 235 <option role="hg-opt-global">--exclude</option>, gives you a
bos@559 236 way to <emphasis>avoid</emphasis> processing files, if they
bos@559 237 match this pattern.</para>
bos@559 238 </listitem></itemizedlist>
bos@559 239 <para>You can provide multiple <option
bos@559 240 role="hg-opt-global">-I</option> and <option
bos@559 241 role="hg-opt-global">-X</option> options on the command line,
bos@559 242 and intermix them as you please. Mercurial interprets the
bos@559 243 patterns you provide using glob syntax by default (but you can
bos@559 244 use regexps if you need to).</para>
bos@559 245
bos@559 246 <para>You can read a <option role="hg-opt-global">-I</option>
bos@559 247 filter as <quote>process only the files that match this
bos@559 248 filter</quote>. <!-- &interaction.filenames.filter.include;
bos@559 249 --> The <option role="hg-opt-global">-X</option> filter is best
bos@559 250 read as <quote>process only the files that don't match this
bos@559 251 pattern</quote>. <!-- &interaction.filenames.filter.exclude;
bos@559 252 --></para>
bos@559 253
bos@559 254 </sect1>
bos@559 255 <sect1>
bos@559 256 <title>Ignoring unwanted files and directories</title>
bos@559 257
bos@559 258 <para>XXX.</para>
bos@559 259
bos@559 260 </sect1>
bos@559 261 <sect1 id="sec:names:case">
bos@559 262 <title>Case sensitivity</title>
bos@559 263
bos@559 264 <para>If you're working in a mixed development environment that
bos@559 265 contains both Linux (or other Unix) systems and Macs or Windows
bos@559 266 systems, you should keep in the back of your mind the knowledge
bos@559 267 that they treat the case (<quote>N</quote> versus
bos@559 268 <quote>n</quote>) of file names in incompatible ways. This is
bos@559 269 not very likely to affect you, and it's easy to deal with if it
bos@559 270 does, but it could surprise you if you don't know about
bos@559 271 it.</para>
bos@559 272
bos@559 273 <para>Operating systems and filesystems differ in the way they
bos@559 274 handle the <emphasis>case</emphasis> of characters in file and
bos@559 275 directory names. There are three common ways to handle case in
bos@559 276 names.</para>
bos@559 277 <itemizedlist>
bos@559 278 <listitem><para>Completely case insensitive. Uppercase and
bos@559 279 lowercase versions of a letter are treated as identical,
bos@559 280 both when creating a file and during subsequent accesses.
bos@559 281 This is common on older DOS-based systems.</para>
bos@559 282 </listitem>
bos@559 283 <listitem><para>Case preserving, but insensitive. When a file
bos@559 284 or directory is created, the case of its name is stored, and
bos@559 285 can be retrieved and displayed by the operating system.
bos@559 286 When an existing file is being looked up, its case is
bos@559 287 ignored. This is the standard arrangement on Windows and
bos@559 288 MacOS. The names <filename>foo</filename> and
bos@559 289 <filename>FoO</filename> identify the same file. This
bos@559 290 treatment of uppercase and lowercase letters as
bos@559 291 interchangeable is also referred to as <emphasis>case
bos@559 292 folding</emphasis>.</para>
bos@559 293 </listitem>
bos@559 294 <listitem><para>Case sensitive. The case of a name is
bos@559 295 significant at all times. The names <filename>foo</filename>
bos@559 296 and {FoO} identify different files. This is the way Linux
bos@559 297 and Unix systems normally work.</para>
bos@559 298 </listitem></itemizedlist>
bos@559 299
bos@559 300 <para>On Unix-like systems, it is possible to have any or all of
bos@559 301 the above ways of handling case in action at once. For example,
bos@559 302 if you use a USB thumb drive formatted with a FAT32 filesystem
bos@559 303 on a Linux system, Linux will handle names on that filesystem in
bos@559 304 a case preserving, but insensitive, way.</para>
bos@559 305
bos@559 306 <sect2>
bos@559 307 <title>Safe, portable repository storage</title>
bos@559 308
bos@559 309 <para>Mercurial's repository storage mechanism is <emphasis>case
bos@559 310 safe</emphasis>. It translates file names so that they can
bos@559 311 be safely stored on both case sensitive and case insensitive
bos@559 312 filesystems. This means that you can use normal file copying
bos@559 313 tools to transfer a Mercurial repository onto, for example, a
bos@559 314 USB thumb drive, and safely move that drive and repository
bos@559 315 back and forth between a Mac, a PC running Windows, and a
bos@559 316 Linux box.</para>
bos@559 317
bos@559 318 </sect2>
bos@559 319 <sect2>
bos@559 320 <title>Detecting case conflicts</title>
bos@559 321
bos@559 322 <para>When operating in the working directory, Mercurial honours
bos@559 323 the naming policy of the filesystem where the working
bos@559 324 directory is located. If the filesystem is case preserving,
bos@559 325 but insensitive, Mercurial will treat names that differ only
bos@559 326 in case as the same.</para>
bos@559 327
bos@559 328 <para>An important aspect of this approach is that it is
bos@559 329 possible to commit a changeset on a case sensitive (typically
bos@559 330 Linux or Unix) filesystem that will cause trouble for users on
bos@559 331 case insensitive (usually Windows and MacOS) users. If a
bos@559 332 Linux user commits changes to two files, one named
bos@559 333 <filename>myfile.c</filename> and the other named
bos@559 334 <filename>MyFile.C</filename>, they will be stored correctly
bos@559 335 in the repository. And in the working directories of other
bos@559 336 Linux users, they will be correctly represented as separate
bos@559 337 files.</para>
bos@559 338
bos@559 339 <para>If a Windows or Mac user pulls this change, they will not
bos@559 340 initially have a problem, because Mercurial's repository
bos@559 341 storage mechanism is case safe. However, once they try to
bos@559 342 <command role="hg-cmd">hg update</command> the working
bos@559 343 directory to that changeset, or <command role="hg-cmd">hg
bos@559 344 merge</command> with that changeset, Mercurial will spot the
bos@559 345 conflict between the two file names that the filesystem would
bos@559 346 treat as the same, and forbid the update or merge from
bos@559 347 occurring.</para>
bos@559 348
bos@559 349 </sect2>
bos@559 350 <sect2>
bos@559 351 <title>Fixing a case conflict</title>
bos@559 352
bos@559 353 <para>If you are using Windows or a Mac in a mixed environment
bos@559 354 where some of your collaborators are using Linux or Unix, and
bos@559 355 Mercurial reports a case folding conflict when you try to
bos@559 356 <command role="hg-cmd">hg update</command> or <command
bos@559 357 role="hg-cmd">hg merge</command>, the procedure to fix the
bos@559 358 problem is simple.</para>
bos@559 359
bos@559 360 <para>Just find a nearby Linux or Unix box, clone the problem
bos@559 361 repository onto it, and use Mercurial's <command
bos@559 362 role="hg-cmd">hg rename</command> command to change the
bos@559 363 names of any offending files or directories so that they will
bos@559 364 no longer cause case folding conflicts. Commit this change,
bos@559 365 <command role="hg-cmd">hg pull</command> or <command
bos@559 366 role="hg-cmd">hg push</command> it across to your Windows or
bos@559 367 MacOS system, and <command role="hg-cmd">hg update</command>
bos@559 368 to the revision with the non-conflicting names.</para>
bos@559 369
bos@559 370 <para>The changeset with case-conflicting names will remain in
bos@559 371 your project's history, and you still won't be able to
bos@559 372 <command role="hg-cmd">hg update</command> your working
bos@559 373 directory to that changeset on a Windows or MacOS system, but
bos@559 374 you can continue development unimpeded.</para>
bos@559 375
bos@559 376 <note>
bos@559 377 <para> Prior to version 0.9.3, Mercurial did not use a case
bos@559 378 safe repository storage mechanism, and did not detect case
bos@559 379 folding conflicts. If you are using an older version of
bos@559 380 Mercurial on Windows or MacOS, I strongly recommend that you
bos@559 381 upgrade.</para>
bos@559 382 </note>
bos@559 383
bos@559 384 </sect2>
bos@559 385 </sect1>
bos@559 386 </chapter>
bos@559 387
bos@559 388 <!--
bos@559 389 local variables:
bos@559 390 sgml-parent-document: ("00book.xml" "book" "chapter")
bos@559 391 end:
bos@559 392 -->