
bos@133: \chapter{File names and pattern matching}
bos@133: \label{chap:names}
bos@133: 
bos@133: Mercurial provides mechanisms that let you work with file names in a
bos@133: consistent and expressive way.
bos@133: 
bos@133: \section{Simple file naming}
bos@133: 
bos@133: Mercurial uses a unified piece of machinery ``under the hood'' to
bos@133: handle file names.  Every command behaves uniformly with respect to
bos@133: file names.  The way in which commands work with file names is as
bos@133: follows.
bos@133: 
bos@133: If you explicitly name real files on the command line, Mercurial works
bos@133: with exactly those files, as you would expect.
bos@133: \interaction{filenames.files}
bos@133: 
bos@133: When you provide a directory name, Mercurial will interpret this as
bos@133: ``operate on every file in this directory and its subdirectories''.
bos@133: Mercurial traverses the files and subdirectories in a directory in
bos@133: alphabetical order.  When it encounters a subdirectory, it will
bos@133: traverse that subdirectory before continuing with the current
bos@133: directory.
bos@133: \interaction{filenames.dirs}
bos@133: 
bos@133: \section{Running commands without any file names}
bos@133: 
bos@133: Mercurial's commands that work with file names have useful default
bos@133: behaviours when you invoke them without providing any file names or
bos@133: patterns.  What kind of behaviour you should expect depends on what
bos@133: the command does.  Here are a few rules of thumb you can use to
bos@133: predict what a command is likely to do if you don't give it any names
bos@133: to work with.
bos@133: \begin{itemize}
bos@133: \item Most commands will operate on the entire working directory.
bos@133:   This is what the \hgcmd{add} command does, for example.
bos@133: \item If the command has effects that are difficult or impossible to
bos@133:   reverse, it will force you to explicitly provide at least one name
bos@133:   or pattern (see below).  This protects you from accidentally
bos@133:   deleting files by running \hgcmd{remove} with no arguments, for
bos@133:   example.
bos@133: \end{itemize}
bos@133: 
bos@133: It's easy to work around these default behaviours if they don't suit
bos@133: you.  If a command normally operates on the whole working directory,
bos@133: you can invoke it on just the current directory and its subdirectories
bos@133: by giving it the name ``\dirname{.}''.
bos@133: \interaction{filenames.wdir-subdir}
bos@133: 
bos@133: Along the same lines, some commands normally print file names relative
bos@133: to the root of the repository, even if you're invoking them from a
bos@133: subdirectory.  Such a command will print file names relative to your
bos@133: subdirectory if you give it explicit names.  Here, we're going to run
bos@133: \hgcmd{status} from a subdirectory, and get it to operate on the
bos@133: entire working directory while printing file names relative to our
bos@133: subdirectory, by passing it the output of the \hgcmd{root} command.
bos@133: \interaction{filenames.wdir-relname}
bos@133: 
bos@133: \section{Telling you what's going on}
bos@133: 
bos@133: The \hgcmd{add} example in the preceding section illustrates something
bos@133: else that's helpful about Mercurial commands.  If a command operates
bos@133: on a file that you didn't name explicitly on the command line, it will
bos@133: usually print the name of the file, so that you will not be surprised
bos@133: what's going on.
bos@133: 
bos@133: The principle here is of \emph{least surprise}.  If you've exactly
bos@133: named a file on the command line, there's no point in repeating it
bos@133: back at you.  If Mercurial is acting on a file \emph{implicitly},
bos@133: because you provided no names, or a directory, or a pattern (see
bos@133: below), it's safest to tell you what it's doing.
bos@133: 
bos@133: For commands that behave this way, you can silence them using the
bos@133: \hggopt{-q} option.  You can also get them to print the name of every
bos@133: file, even those you've named explicitly, using the \hggopt{-v}
bos@133: option.
bos@133: 
bos@133: \section{Using patterns to identify files}
bos@133: 
bos@133: In addition to working with file and directory names, Mercurial lets
bos@133: you use \emph{patterns} to identify files.  Mercurial's pattern
bos@133: handling is expressive.
bos@133: 
bos@133: On Unix-like systems (Linux, MacOS, etc.), the job of matching file
bos@133: names to patterns normally falls to the shell.  On these systems, you
bos@133: must explicitly tell Mercurial that a name is a pattern.  On Windows,
bos@133: the shell does not expand patterns, so Mercurial will automatically
bos@133: identify names that are patterns, and expand them for you.
bos@133: 
bos@133: To provide a pattern in place of a regular name on the command line,
bos@133: the mechanism is simple:
bos@133: \begin{codesample2}
bos@133:   syntax:patternbody
bos@133: \end{codesample2}
bos@133: That is, a pattern is identified by a short text string that says what
bos@133: kind of pattern this is, followed by a colon, followed by the actual
bos@133: pattern.
bos@133: 
bos@133: Mercurial supports two kinds of pattern syntax.  The most frequently
bos@133: used is called \texttt{glob}; this is the same kind of pattern
bos@133: matching used by the Unix shell, and should be familiar to Windows
bos@133: command prompt users, too.  
bos@133: 
bos@133: When Mercurial does automatic pattern matching on Windows, it uses
bos@133: \texttt{glob} syntax.  You can thus omit the ``\texttt{glob:}'' prefix
bos@133: on Windows, but it's safe to use it, too.
bos@133: 
bos@133: The \texttt{re} syntax is more powerful; it lets you specify patterns
bos@133: using regular expressions, also known as regexps.
bos@133: 
bos@133: By the way, in the examples that follow, notice that I'm careful to
bos@133: wrap all of my patterns in quote characters, so that they won't get
bos@133: expanded by the shell before Mercurial sees them.
bos@133: 
bos@133: \subsection{Shell-style \texttt{glob} patterns}
bos@133: 
bos@133: This is an overview of the kinds of patterns you can use when you're
bos@133: matching on glob patterns.
bos@133: 
bos@133: The ``\texttt{*}'' character matches any string, within a single
bos@133: directory.
bos@133: \interaction{filenames.glob.star}
bos@133: 
bos@133: The ``\texttt{**}'' pattern matches any string, and crosses directory
bos@133: boundaries.  It's not a standard Unix glob token, but it's accepted by
bos@133: several popular Unix shells, and is very useful.
bos@133: \interaction{filenames.glob.starstar}
bos@133: 
bos@133: The ``\texttt{?}'' pattern matches any single character.
bos@133: \interaction{filenames.glob.question}
bos@133: 
bos@133: The ``\texttt{[}'' character begins a \emph{character class}.  This
bos@133: matches any single character within the class.  The class ends with a
bos@133: ``\texttt{]}'' character.  A class may contain multiple \emph{range}s
bos@133: of the form ``\texttt{a-f}'', which is shorthand for
bos@133: ``\texttt{abcdef}''.
bos@133: \interaction{filenames.glob.range}
bos@133: If the first character after the ``\texttt{[}'' in a character class
bos@133: is a ``\texttt{!}'', it \emph{negates} the class, making it match any
bos@133: single character not in the class.
bos@133: 
bos@133: A ``\texttt{\{}'' begins a group of subpatterns, where the whole group
bos@133: matches if any subpattern in the group matches.  The ``\texttt{,}''
bos@133: character separates subpatterns, and ``\texttt{\}}'' ends the group.
bos@133: \interaction{filenames.glob.group}
bos@133: 
bos@133: \subsubsection{Watch out!}
bos@133: 
bos@133: Don't forget that if you want to match a pattern in any directory, you
bos@133: should not be using the ``\texttt{*}'' match-any token, as this will
bos@133: only match within one directory.  Instead, use the ``\texttt{**}''
bos@133: token.  This small example illustrates the difference between the two.
bos@133: \interaction{filenames.glob.star-starstar}
bos@133: 
bos@133: \subsection{Regular expression matching with \texttt{re} patterns}
bos@133: 
bos@133: Mercurial accepts the same regular expression syntax as the Python
bos@133: programming language (it uses Python's regexp engine internally).
bos@133: This is based on the Perl language's regexp syntax, which is the most
bos@133: popular dialect in use (it's also used in Java, for example).
bos@133: 
bos@133: I won't discuss Mercurial's regexp dialect in any detail here, as
bos@133: regexps are not often used.  Perl-style regexps are in any case
bos@133: already exhaustively documented on a multitude of web sites, and in
bos@133: many books.  Instead, I will focus here on a few things you should
bos@133: know if you find yourself needing to use regexps with Mercurial.
bos@133: 
bos@133: A regexp is matched against an entire file name, relative to the root
bos@133: of the repository.  In other words, even if you're already in
bos@133: subbdirectory \dirname{foo}, if you want to match files under this
bos@133: directory, your pattern must start with ``\texttt{foo/}''.
bos@133: 
bos@133: One thing to note, if you're familiar with Perl-style regexps, is that
bos@133: Mercurial's are \emph{rooted}.  That is, a regexp starts matching
bos@133: against the beginning of a string; it doesn't look for a match
arne@264: anywhere within the string.  To match anywhere in a string, start
bos@133: your pattern with ``\texttt{.*}''.
bos@133: 
bos@133: \section{Filtering files}
bos@133: 
bos@133: Not only does Mercurial give you a variety of ways to specify files;
bos@133: it lets you further winnow those files using \emph{filters}.  Commands
bos@133: that work with file names accept two filtering options.
bos@133: \begin{itemize}
bos@133: \item \hggopt{-I}, or \hggopt{--include}, lets you specify a pattern
bos@133:   that file names must match in order to be processed.
bos@133: \item \hggopt{-X}, or \hggopt{--exclude}, gives you a way to
bos@133:   \emph{avoid} processing files, if they match this pattern.
bos@133: \end{itemize}
bos@133: You can provide multiple \hggopt{-I} and \hggopt{-X} options on the
bos@133: command line, and intermix them as you please.  Mercurial interprets
bos@133: the patterns you provide using glob syntax by default (but you can use
bos@133: regexps if you need to).
bos@133: 
bos@133: You can read a \hggopt{-I} filter as ``process only the files that
bos@133: match this filter''.
bos@133: \interaction{filenames.filter.include}
bos@133: The \hggopt{-X} filter is best read as ``process only the files that
bos@133: don't match this pattern''.
bos@133: \interaction{filenames.filter.exclude}
bos@133: 
bos@133: \section{Ignoring unwanted files and directories}
bos@133: 
bos@133: XXX.
bos@133: 
bos@133: \section{Case sensitivity}
bos@133: \label{sec:names:case}
bos@133: 
bos@133: If you're working in a mixed development environment that contains
bos@133: both Linux (or other Unix) systems and Macs or Windows systems, you
bos@133: should keep in the back of your mind the knowledge that they treat the
bos@133: case (``N'' versus ``n'') of file names in incompatible ways.  This is
bos@133: not very likely to affect you, and it's easy to deal with if it does,
bos@133: but it could surprise you if you don't know about it.
bos@133: 
bos@133: Operating systems and filesystems differ in the way they handle the
bos@133: \emph{case} of characters in file and directory names.  There are
bos@133: three common ways to handle case in names.
bos@133: \begin{itemize}
bos@133: \item Completely case insensitive.  Uppercase and lowercase versions
bos@133:   of a letter are treated as identical, both when creating a file and
bos@133:   during subsequent accesses.  This is common on older DOS-based
bos@133:   systems.
bos@133: \item Case preserving, but insensitive.  When a file or directory is
bos@133:   created, the case of its name is stored, and can be retrieved and
bos@133:   displayed by the operating system.  When an existing file is being
bos@133:   looked up, its case is ignored.  This is the standard arrangement on
bos@133:   Windows and MacOS.  The names \filename{foo} and \filename{FoO}
bos@133:   identify the same file.  This treatment of uppercase and lowercase
bos@133:   letters as interchangeable is also referred to as \emph{case
bos@133:     folding}.
bos@133: \item Case sensitive.  The case of a name is significant at all times.
bos@133:   The names \filename{foo} and {FoO} identify different files.  This
bos@133:   is the way Linux and Unix systems normally work.
bos@133: \end{itemize}
bos@133: 
bos@133: On Unix-like systems, it is possible to have any or all of the above
bos@133: ways of handling case in action at once.  For example, if you use a
bos@133: USB thumb drive formatted with a FAT32 filesystem on a Linux system,
bos@133: Linux will handle names on that filesystem in a case preserving, but
bos@133: insensitive, way.
bos@133: 
bos@133: \subsection{Safe, portable repository storage}
bos@133: 
bos@133: Mercurial's repository storage mechanism is \emph{case safe}.  It
bos@133: translates file names so that they can be safely stored on both case
bos@133: sensitive and case insensitive filesystems.  This means that you can
bos@133: use normal file copying tools to transfer a Mercurial repository onto,
bos@133: for example, a USB thumb drive, and safely move that drive and
bos@133: repository back and forth between a Mac, a PC running Windows, and a
bos@133: Linux box.
bos@133: 
bos@133: \subsection{Detecting case conflicts}
bos@133: 
bos@133: When operating in the working directory, Mercurial honours the naming
bos@133: policy of the filesystem where the working directory is located.  If
bos@133: the filesystem is case preserving, but insensitive, Mercurial will
bos@133: treat names that differ only in case as the same.
bos@133: 
bos@133: An important aspect of this approach is that it is possible to commit
bos@133: a changeset on a case sensitive (typically Linux or Unix) filesystem
bos@133: that will cause trouble for users on case insensitive (usually Windows
bos@133: and MacOS) users.  If a Linux user commits changes to two files, one
bos@133: named \filename{myfile.c} and the other named \filename{MyFile.C},
bos@133: they will be stored correctly in the repository.  And in the working
bos@133: directories of other Linux users, they will be correctly represented
bos@133: as separate files.
bos@133: 
bos@133: If a Windows or Mac user pulls this change, they will not initially
bos@133: have a problem, because Mercurial's repository storage mechanism is
bos@133: case safe.  However, once they try to \hgcmd{update} the working
bos@133: directory to that changeset, or \hgcmd{merge} with that changeset,
bos@133: Mercurial will spot the conflict between the two file names that the
bos@133: filesystem would treat as the same, and forbid the update or merge
bos@133: from occurring.
bos@133: 
bos@133: \subsection{Fixing a case conflict}
bos@133: 
bos@133: If you are using Windows or a Mac in a mixed environment where some of
bos@133: your collaborators are using Linux or Unix, and Mercurial reports a
bos@133: case folding conflict when you try to \hgcmd{update} or \hgcmd{merge},
bos@133: the procedure to fix the problem is simple.
bos@133: 
bos@133: Just find a nearby Linux or Unix box, clone the problem repository
bos@133: onto it, and use Mercurial's \hgcmd{rename} command to change the
bos@133: names of any offending files or directories so that they will no
bos@133: longer cause case folding conflicts.  Commit this change, \hgcmd{pull}
bos@133: or \hgcmd{push} it across to your Windows or MacOS system, and
bos@133: \hgcmd{update} to the revision with the non-conflicting names.
bos@133: 
bos@133: The changeset with case-conflicting names will remain in your
bos@133: project's history, and you still won't be able to \hgcmd{update} your
bos@133: working directory to that changeset on a Windows or MacOS system, but
bos@133: you can continue development unimpeded.
bos@133: 
bos@133: \begin{note}
bos@133:   Prior to version~0.9.3, Mercurial did not use a case safe repository
bos@133:   storage mechanism, and did not detect case folding conflicts.  If
bos@133:   you are using an older version of Mercurial on Windows or MacOS, I
bos@133:   strongly recommend that you upgrade.
bos@133: \end{note}
bos@133: 
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bos@133: %%% TeX-master: "00book"
bos@133: %%% End: 




