@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003,
-@c 2004, 2005, 2006 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
+@c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/files
@node Files, Backups and Auto-Saving, Documentation, Top
@var{filename}.
@end deffn
-@tindex find-file-wildcards
@defopt find-file-wildcards
If this variable is non-@code{nil}, then the various @code{find-file}
commands check for wildcard characters and visit all the files that
@node Saving Buffers
@section Saving Buffers
+@cindex saving buffers
When you edit a file in Emacs, you are actually working on a buffer
that is visiting that file---that is, the contents of the file are
@end deffn
Saving a buffer runs several hooks. It also performs format
-conversion (@pxref{Format Conversion}), and may save text properties in
-``annotations'' (@pxref{Saving Properties}).
+conversion (@pxref{Format Conversion}).
@defvar write-file-functions
The value of this variable is a list of functions to be called before
@node Reading from Files
@comment node-name, next, previous, up
@section Reading from Files
+@cindex reading from files
You can copy a file from the disk and insert it into a buffer
using the @code{insert-file-contents} function. Don't use the user-level
The function @code{insert-file-contents} checks the file contents
against the defined file formats, and converts the file contents if
-appropriate. @xref{Format Conversion}. It also calls the functions in
-the list @code{after-insert-file-functions}; see @ref{Saving
-Properties}. Normally, one of the functions in the
+appropriate and also calls the functions in
+the list @code{after-insert-file-functions}. @xref{Format Conversion}.
+Normally, one of the functions in the
@code{after-insert-file-functions} list determines the coding system
(@pxref{Coding Systems}) used for decoding the file's contents,
including end-of-line conversion.
@node Writing to Files
@comment node-name, next, previous, up
@section Writing to Files
+@cindex writing to files
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the @code{append-to-file} and
@var{filename} and @var{visit} for that purpose.
The function @code{write-region} converts the data which it writes to
-the appropriate file formats specified by @code{buffer-file-format}.
-@xref{Format Conversion}. It also calls the functions in the list
-@code{write-region-annotate-functions}; see @ref{Saving Properties}.
+the appropriate file formats specified by @code{buffer-file-format}
+and also calls the functions in the list
+@code{write-region-annotate-functions}.
+@xref{Format Conversion}.
Normally, @code{write-region} displays the message @samp{Wrote
@var{filename}} in the echo area. If @var{visit} is neither @code{t}
@node File Locks
@section File Locks
@cindex file locks
+@cindex lock file
When two users edit the same file at the same time, they are likely
to interfere with each other. Emacs tries to prevent this situation
stored in the same directory as the file you are editing.
When you access files using NFS, there may be a small probability that
-you and another user will both lock the same file ``simultaneously''.
+you and another user will both lock the same file ``simultaneously.''
If this happens, it is possible for the two users to make changes
simultaneously, but Emacs will still warn the user who saves second.
Also, the detection of modification of a buffer visiting a file changed
@node Information about Files
@section Information about Files
+@cindex file, information about
The functions described in this section all operate on strings that
designate file names. With a few exceptions, all the functions have
(@pxref{Changing Files}).
@item
-The file's @acronym{UID} as a string or an integer. If a string
-value cannot be looked up, the integer value is returned.
+The file's @acronym{UID}, normally as a string. However, if it does
+not correspond to a named user, the value is an integer or a floating
+point number.
@item
-The file's @acronym{GID} likewise.
+The file's @acronym{GID}, likewise.
@item
The time of last access, as a list of two integers.
@item
The time of last modification as a list of two integers (as above).
+@cindex modification time of file
@item
The time of last status change as a list of two integers (as above).
@node Locating Files
@subsection How to Locate Files in Standard Places
-@cindex locate files
-@cindex find files
+@cindex locate file in path
+@cindex find file in path
This section explains how to search for a file in a list of
-directories. One example is when you need to look for a program's
-executable file, e.g., to find out whether a given program is
-installed on the user's system. Another example is the search for
+directories (a @dfn{path}). One example is when you need to look for
+a program's executable file, e.g., to find out whether a given program
+is installed on the user's system. Another example is the search for
Lisp libraries (@pxref{Library Search}). Such searches generally need
to try various possible file name extensions, in addition to various
possible directories. Emacs provides a function for such a
a list of one or more of these symbols.
@end defun
-@cindex find executable program
@defun executable-find program
This function searches for the executable file of the named
@var{program} and returns the full absolute name of the executable,
@node Changing Files
@section Changing File Names and Attributes
-@cindex renaming files
+@c @cindex renaming files Duplicates rename-file
@cindex copying files
@cindex deleting files
@cindex linking files
@end defun
@defun file-name-extension filename &optional period
-This function returns @var{filename}'s final ``extension'', if any,
+This function returns @var{filename}'s final ``extension,'' if any,
after applying @code{file-name-sans-versions} to remove any
version/backup part. The extension, in a file name, is the part that
starts with the last @samp{.} in the last name component (minus
Andrew Innes says that this
@c @defvar directory-sep-char
-@c @tindex directory-sep-char
This variable holds the character that Emacs normally uses to separate
file name components. The default value is @code{?/}, but on MS-Windows
you can set it to @code{?\\}; then the functions that transform file names
@end group
@end example
+In some cases, a leading @samp{..} component can remain in the output:
+
+@example
+@group
+(expand-file-name "../home" "/")
+ @result{} "/../home"
+@end group
+@end example
+
+@noindent
+This is for the sake of filesystems that have the concept of a
+``superroot'' above the root directory @file{/}. On other filesystems,
+@file{/../} is interpreted exactly the same as @file{/}.
+
Note that @code{expand-file-name} does @emph{not} expand environment
variables; only @code{substitute-in-file-name} does that.
two different jobs from trying to use the exact same file name.
@defun make-temp-file prefix &optional dir-flag suffix
-@tindex make-temp-file
This function creates a temporary file and returns its name. Emacs
creates the temporary file's name by adding to @var{prefix} some
random characters that are different in each Emacs job. The result is
non-@code{nil}.
@end defvar
-@tindex small-temporary-file-directory
@defvar small-temporary-file-directory
This variable specifies the directory name for
creating certain temporary files, which are likely to be small.
@cindex completion, file name
This section describes low-level subroutines for completing a file
-name. For other completion functions, see @ref{Completion}.
+name. For higher level functions, see @ref{Reading File Names}.
@defun file-name-all-completions partial-filename directory
This function returns a list of all possible completions for a file
@end example
@end defun
-@defun file-name-completion filename directory
+@defun file-name-completion filename directory &optional predicate
This function completes the file name @var{filename} in directory
@var{directory}. It returns the longest prefix common to all file names
-in directory @var{directory} that start with @var{filename}.
+in directory @var{directory} that start with @var{filename}. If
+@var{predicate} is non-@code{nil} then it ignores possible completions
+that don't satisfy @var{predicate}, after calling that function
+with one argument, the expanded absolute file name.
If only one match exists and @var{filename} matches it exactly, the
function returns @code{t}. The function returns @code{nil} if directory
@var{file} in directory @var{dirname}. It is only available on VMS.
@end defun
-@tindex file-expand-wildcards
@defun file-expand-wildcards pattern &optional full
This function expands the wildcard pattern @var{pattern}, returning
a list of file names that match it.
@node Create/Delete Dirs
@section Creating and Deleting Directories
+@cindex creating and deleting directories
@c Emacs 19 features
Most Emacs Lisp file-manipulation functions get errors when used on
is chosen so that handlers for jobs such as uncompression are handled
first, before handlers for jobs such as remote file access.
-Here are the operations that a magic file name handler gets to handle:
+ Here are the operations that a magic file name handler gets to handle:
@ifnottex
@noindent
@code{directory-file-name},
@code{directory-files},
@code{directory-files-and-attributes},
-@code{dired-call-process},
@code{dired-compress-file}, @code{dired-uncache},@*
@code{expand-file-name},
@code{file-accessible-directory-p},
@code{make-directory},
@code{make-directory-internal},
@code{make-symbolic-link},@*
+@code{process-file},
@code{rename-file}, @code{set-file-modes}, @code{set-file-times},
@code{set-visited-file-modtime}, @code{shell-command},
+@code{start-file-process},
@code{substitute-in-file-name},@*
@code{unhandled-file-name-directory},
@code{vc-registered},
@code{directory-file-name},
@code{directory-files},
@code{directory-files-and-at@discretionary{}{}{}tributes},
-@code{dired-call-process},
@code{dired-compress-file}, @code{dired-uncache},
@code{expand-file-name},
@code{file-accessible-direc@discretionary{}{}{}tory-p},
@code{load}, @code{make-direc@discretionary{}{}{}tory},
@code{make-direc@discretionary{}{}{}tory-internal},
@code{make-symbolic-link},
+@code{process-file},
@code{rename-file}, @code{set-file-modes},
@code{set-visited-file-modtime}, @code{shell-command},
+@code{start-file-process},
@code{substitute-in-file-name},
@code{unhandled-file-name-directory},
@code{vc-regis@discretionary{}{}{}tered},
possibly others to be added in the future. It need not implement all
these operations itself---when it has nothing special to do for a
certain operation, it can reinvoke the primitive, to handle the
-operation ``in the usual way''. It should always reinvoke the primitive
+operation ``in the usual way.'' It should always reinvoke the primitive
for an operation it does not recognize. Here's one way to do this:
@smallexample
functions, so that they won't be loaded except when they have real
work to do.
+ Simply deferring all operations to the usual primitives does not
+work. For instance, if the file name handler applies to
+@code{file-exists-p}, then it must handle @code{load} itself, because
+the usual @code{load} code won't work properly in that case. However,
+if the handler uses the @code{operations} property to say it doesn't
+handle @code{file-exists-p}, then it need not handle @code{load}
+nontrivially.
+
@defvar inhibit-file-name-handlers
This variable holds a list of handlers whose use is presently inhibited
for a certain operation.
of the local copy file.
@end defun
-@defun file-remote-p filename
+@defun file-remote-p filename &optional identification connected
This function tests whether @var{filename} is a remote file. If
@var{filename} is local (not remote), the return value is @code{nil}.
If @var{filename} is indeed remote, the return value is a string that
This identifier string can include a host name and a user name, as
well as characters designating the method used to access the remote
system. For example, the remote identifier string for the filename
-@code{/ssh:user@@host:/some/file} is @code{/ssh:user@@host:}.
+@code{/sudo::/some/file} is @code{/sudo:root@@localhost:}.
If @code{file-remote-p} returns the same identifier for two different
filenames, that means they are stored on the same file system and can
example, that it is possible to start a remote process accessing both
files at the same time. Implementors of file handlers need to ensure
this principle is valid.
+
+@var{identification} specifies which part of the identifier shall be
+returned as string. @var{identification} can be the symbol
+@code{method}, @code{user} or @code{host}; any other value is handled
+like @code{nil} and means to return the complete identifier string.
+In the example above, the remote @code{user} identifier string would
+be @code{root}.
+
+If @var{connected} is non-@code{nil}, this function returns @code{nil}
+even if @var{filename} is remote, if Emacs has no network connection
+to its host. This is useful when you want to avoid the delay of
+making connections when they don't exist.
@end defun
@defun unhandled-file-name-directory filename
@cindex file format conversion
@cindex encoding file formats
@cindex decoding file formats
- The variable @code{format-alist} defines a list of @dfn{file formats},
-which describe textual representations used in files for the data (text,
-text-properties, and possibly other information) in an Emacs buffer.
-Emacs performs format conversion if appropriate when reading and writing
-files.
+@cindex text properties in files
+@cindex saving text properties
+ Emacs performs several steps to convert the data in a buffer (text,
+text properties, and possibly other information) to and from a
+representation suitable for storing into a file. This section describes
+the fundamental functions that perform this @dfn{format conversion},
+namely @code{insert-file-contents} for reading a file into a buffer,
+and @code{write-region} for writing a buffer into a file.
+
+@menu
+* Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}
+* Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}.
+* Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion.
+@end menu
+
+@node Format Conversion Overview
+@subsection Overview
+@noindent
+The function @code{insert-file-contents}:
+
+@itemize
+@item initially, inserts bytes from the file into the buffer;
+@item decodes bytes to characters as appropriate;
+@item processes formats as defined by entries in @code{format-alist}; and
+@item calls functions in @code{after-insert-file-functions}.
+@end itemize
+
+@noindent
+The function @code{write-region}:
+
+@itemize
+@item initially, calls functions in @code{write-region-annotate-functions};
+@item processes formats as defined by entries in @code{format-alist};
+@item encodes characters to bytes as appropriate; and
+@item modifies the file with the bytes.
+@end itemize
+
+ This shows the symmetry of the lowest-level operations; reading and
+writing handle things in opposite order. The rest of this section
+describes the two facilities surrounding the three variables named
+above, as well as some related functions. @ref{Coding Systems}, for
+details on character encoding and decoding.
+
+@node Format Conversion Round-Trip
+@subsection Round-Trip Specification
+
+ The most general of the two facilities is controlled by the variable
+@code{format-alist}, a list of @dfn{file format} specifications, which
+describe textual representations used in files for the data in an Emacs
+buffer. The descriptions for reading and writing are paired, which is
+why we call this ``round-trip'' specification
+(@pxref{Format Conversion Piecemeal}, for non-paired specification).
@defvar format-alist
This list contains one format definition for each defined file format.
-@end defvar
-
-@cindex format definition
Each format definition is a list of this form:
@example
(@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn})
@end example
+@end defvar
+@cindex format definition
+@noindent
Here is what the elements in a format definition mean:
@table @var
If @var{to-fn} is a string, it is a shell command; Emacs runs the
command as a filter to perform the conversion.
-If @var{to-fn} is a function, it is called with two arguments, @var{begin}
-and @var{end}, which specify the part of the buffer it should convert.
-There are two ways it can do the conversion:
+If @var{to-fn} is a function, it is called with three arguments:
+@var{begin} and @var{end}, which specify the part of the buffer it
+should convert, and @var{buffer}, which specifies which buffer. There
+are two ways it can do the conversion:
@itemize @bullet
@item
in all buffers.
@end defvar
+@node Format Conversion Piecemeal
+@subsection Piecemeal Specification
+
+ In contrast to the round-trip specification described in the previous
+subsection (@pxref{Format Conversion Round-Trip}), you can use the variables
+@code{after-insert-file-functions} and @code{write-region-annotate-functions}
+to separately control the respective reading and writing conversions.
+
+ Conversion starts with one representation and produces another
+representation. When there is only one conversion to do, there is no
+conflict about what to start with. However, when there are multiple
+conversions involved, conflict may arise when two conversions need to
+start with the same data.
+
+ This situation is best understood in the context of converting text
+properties during @code{write-region}. For example, the character at
+position 42 in a buffer is @samp{X} with a text property @code{foo}. If
+the conversion for @code{foo} is done by inserting into the buffer, say,
+@samp{FOO:}, then that changes the character at position 42 from
+@samp{X} to @samp{F}. The next conversion will start with the wrong
+data straight away.
+
+ To avoid conflict, cooperative conversions do not modify the buffer,
+but instead specify @dfn{annotations}, a list of elements of the form
+@code{(@var{position} . @var{string})}, sorted in order of increasing
+@var{position}.
+
+ If there is more than one conversion, @code{write-region} merges their
+annotations destructively into one sorted list. Later, when the text
+from the buffer is actually written to the file, it intermixes the
+specified annotations at the corresponding positions. All this takes
+place without modifying the buffer.
+
+@c ??? What about ``overriding'' conversions like those allowed
+@c ??? for `write-region-annotate-functions', below? --ttn
+
+ In contrast, when reading, the annotations intermixed with the text
+are handled immediately. @code{insert-file-contents} sets point to the
+beginning of some text to be converted, then calls the conversion
+functions with the length of that text. These functions should always
+return with point at the beginning of the inserted text. This approach
+makes sense for reading because annotations removed by the first
+converter can't be mistakenly processed by a later converter.
+
+ Each conversion function should scan for the annotations it
+recognizes, remove the annotation, modify the buffer text (to set a text
+property, for example), and return the updated length of the text, as it
+stands after those changes. The value returned by one function becomes
+the argument to the next function.
+
+@defvar write-region-annotate-functions
+A list of functions for @code{write-region} to call. Each function in
+the list is called with two arguments: the start and end of the region
+to be written. These functions should not alter the contents of the
+buffer. Instead, they should return annotations.
+
+@c ??? Following adapted from comment in `build_annotations' (fileio.c).
+@c ??? Perhaps this is intended for internal use only?
+@c ??? Someone who understands this, please reword it. --ttn
+As a special case, if a function returns with a different buffer
+current, Emacs takes it to mean the current buffer contains altered text
+to be output, and discards all previous annotations because they should
+have been dealt with by this function.
+@end defvar
+
+@defvar after-insert-file-functions
+Each function in this list is called by @code{insert-file-contents}
+with one argument, the number of characters inserted, and with point
+at the beginning of the inserted text. Each function should leave
+point unchanged, and return the new character count describing the
+inserted text as modified by the function.
+@c ??? The docstring mentions a handler from `file-name-handler-alist'
+@c "intercepting" `insert-file-contents'. Hmmm. --ttn
+@end defvar
+
+ We invite users to write Lisp programs to store and retrieve text
+properties in files, using these hooks, and thus to experiment with
+various data formats and find good ones. Eventually we hope users
+will produce good, general extensions we can install in Emacs.
+
+ We suggest not trying to handle arbitrary Lisp objects as text property
+names or values---because a program that general is probably difficult
+to write, and slow. Instead, choose a set of possible data types that
+are reasonably flexible, and not too hard to encode.
+
@ignore
arch-tag: 141f74ce-6ae3-40dc-a6c4-ef83fc4ec35c
@end ignore
HCoop / bpt / emacs.git / blobdiff