This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2) v3.2, April, May 1997 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: lispref.info, Node: Accessing Documentation, Next: Keys in Documentation, Prev: Documentation Basics, Up: Documentation Access to Documentation Strings =============================== - Function: documentation-property SYMBOL PROPERTY &optional VERBATIM This function returns the documentation string that is recorded in SYMBOL's property list under property PROPERTY. It retrieves the text from a file if necessary, and runs `substitute-command-keys' to substitute actual key bindings. (This substitution is not done if VERBATIM is non-`nil'; the VERBATIM argument exists only as of Emacs 19.) (documentation-property 'command-line-processed 'variable-documentation) => "t once command line has been processed" (symbol-plist 'command-line-processed) => (variable-documentation 188902) - Function: documentation FUNCTION &optional VERBATIM This function returns the documentation string of FUNCTION. It reads the text from a file if necessary. Then (unless VERBATIM is non-`nil') it calls `substitute-command-keys', to return a value containing the actual (current) key bindings. The function `documentation' signals a `void-function' error if FUNCTION has no function definition. However, it is ok if the function definition has no documentation string. In that case, `documentation' returns `nil'. Here is an example of using the two functions, `documentation' and `documentation-property', to display the documentation strings for several symbols in a `*Help*' buffer. (defun describe-symbols (pattern) "Describe the XEmacs Lisp symbols matching PATTERN. All symbols that have PATTERN in their name are described in the `*Help*' buffer." (interactive "sDescribe symbols matching: ") (let ((describe-func (function (lambda (s) ;; Print description of symbol. (if (fboundp s) ; It is a function. (princ (format "%s\t%s\n%s\n\n" s (if (commandp s) (let ((keys (where-is-internal s))) (if keys (concat "Keys: " (mapconcat 'key-description keys " ")) "Keys: none")) "Function") (or (documentation s) "not documented")))) (if (boundp s) ; It is a variable. (princ (format "%s\t%s\n%s\n\n" s (if (user-variable-p s) "Option " "Variable") (or (documentation-property s 'variable-documentation) "not documented"))))))) sym-list) ;; Build a list of symbols that match pattern. (mapatoms (function (lambda (sym) (if (string-match pattern (symbol-name sym)) (setq sym-list (cons sym sym-list)))))) ;; Display the data. (with-output-to-temp-buffer "*Help*" (mapcar describe-func (sort sym-list 'string<)) (print-help-return-message)))) The `describe-symbols' function works like `apropos', but provides more information. (describe-symbols "goal") ---------- Buffer: *Help* ---------- goal-column Option *Semipermanent goal column for vertical motion, as set by C-x C-n, or nil. set-goal-column Command: C-x C-n Set the current horizontal position as a goal for C-n and C-p. Those commands will move to this position in the line moved to rather than trying to keep the same horizontal position. With a non-nil argument, clears out the goal column so that C-n and C-p resume vertical motion. The goal column is stored in the variable `goal-column'. temporary-goal-column Variable Current goal column for vertical motion. It is the column where point was at the start of current run of vertical motion commands. When the `track-eol' feature is doing its job, the value is 9999. ---------- Buffer: *Help* ---------- - Function: Snarf-documentation FILENAME This function is used only during XEmacs initialization, just before the runnable XEmacs is dumped. It finds the file offsets of the documentation strings stored in the file FILENAME, and records them in the in-core function definitions and variable property lists in place of the actual strings. *Note Building XEmacs::. XEmacs finds the file FILENAME in the `lib-src' directory. When the dumped XEmacs is later executed, the same file is found in the directory `doc-directory'. The usual value for FILENAME is `DOC', but this can be changed by modifying the variable `internal-doc-file-name'. - Variable: internal-doc-file-name This variable holds the name of the file containing documentation strings of built-in symbols, usually `DOC'. The full pathname of the internal doc file is `(concat doc-directory internal-doc-file-name)'. - Variable: doc-directory This variable holds the name of the directory which contains the "internal doc file" that contains documentation strings for built-in and preloaded functions and variables. In most cases, this is the same as `exec-directory'. They may be different when you run XEmacs from the directory where you built it, without actually installing it. See `exec-directory' in *Note Help Functions::. In older Emacs versions, `exec-directory' was used for this. - Variable: data-directory This variable holds the name of the directory in which XEmacs finds certain system independent documentation and text files that come with XEmacs. In older Emacs versions, `exec-directory' was used for this.  File: lispref.info, Node: Keys in Documentation, Next: Describing Characters, Prev: Accessing Documentation, Up: Documentation Substituting Key Bindings in Documentation ========================================== When documentation strings refer to key sequences, they should use the current, actual key bindings. They can do so using certain special text sequences described below. Accessing documentation strings in the usual way substitutes current key binding information for these special sequences. This works by calling `substitute-command-keys'. You can also call that function yourself. Here is a list of the special sequences and what they mean: `\[COMMAND]' stands for a key sequence that will invoke COMMAND, or `M-x COMMAND' if COMMAND has no key bindings. `\{MAPVAR}' stands for a summary of the value of MAPVAR, which should be a keymap. The summary is made by `describe-bindings'. `\' stands for no text itself. It is used for a side effect: it specifies MAPVAR as the keymap for any following `\[COMMAND]' sequences in this documentation string. `\=' quotes the following character and is discarded; this `\=\=' puts `\=' into the output, and `\=\[' puts `\[' into the output. *Please note:* Each `\' must be doubled when written in a string in XEmacs Lisp. - Function: substitute-command-keys STRING This function scans STRING for the above special sequences and replaces them by what they stand for, returning the result as a string. This permits display of documentation that refers accurately to the user's own customized key bindings. Here are examples of the special sequences: (substitute-command-keys "To abort recursive edit, type: \\[abort-recursive-edit]") => "To abort recursive edit, type: C-]" (substitute-command-keys "The keys that are defined for the minibuffer here are: \\{minibuffer-local-must-match-map}") => "The keys that are defined for the minibuffer here are: ? minibuffer-completion-help SPC minibuffer-complete-word TAB minibuffer-complete LFD minibuffer-complete-and-exit RET minibuffer-complete-and-exit C-g abort-recursive-edit " (substitute-command-keys "To abort a recursive edit from the minibuffer, type\ \\\\[abort-recursive-edit].") => "To abort a recursive edit from the minibuffer, type C-g." (substitute-command-keys "Substrings of the form \\=\\{MAPVAR} are replaced by summaries \(made by describe-bindings) of the value of MAPVAR, taken as a keymap. Substrings of the form \\=\\ specify to use the value of MAPVAR as the keymap for future \\=\\[COMMAND] substrings. \\=\\= quotes the following character and is discarded; thus, \\=\\=\\=\\= puts \\=\\= into the output, and \\=\\=\\=\\[ puts \\=\\[ into the output.") => "Substrings of the form \{MAPVAR} are replaced by summaries (made by describe-bindings) of the value of MAPVAR, taken as a keymap. Substrings of the form \ specify to use the value of MAPVAR as the keymap for future \[COMMAND] substrings. \= quotes the following character and is discarded; thus, \=\= puts \= into the output, and \=\[ puts \[ into the output."  File: lispref.info, Node: Describing Characters, Next: Help Functions, Prev: Keys in Documentation, Up: Documentation Describing Characters for Help Messages ======================================= These functions convert events, key sequences or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself. - Function: key-description SEQUENCE This function returns a string containing the XEmacs standard notation for the input events in SEQUENCE. The argument SEQUENCE may be a string, vector or list. *Note Events::, for more information about valid events. See also the examples for `single-key-description', below. - Function: single-key-description KEY This function returns a string describing KEY in the standard XEmacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with `C-', a meta character turns into a string starting with `M-', and space, linefeed, etc. appear as `SPC', `LFD', etc. A symbol appears as the name of the symbol. An event that is a list appears as the name of the symbol in the CAR of the list. (single-key-description ?\C-x) => "C-x" (key-description "\C-x \M-y \n \t \r \f123") => "C-x SPC M-y SPC LFD SPC TAB SPC RET SPC C-l 1 2 3" (single-key-description 'kp_next) => "kp_next" (single-key-description '(shift button1)) => "Sh-button1" - Function: text-char-description CHARACTER This function returns a string describing CHARACTER in the standard XEmacs notation for characters that appear in text--like `single-key-description', except that control characters are represented with a leading caret (which is how control characters in XEmacs buffers are usually displayed). (text-char-description ?\C-c) => "^C" (text-char-description ?\M-m) => "M-m" (text-char-description ?\C-\M-m) => "M-^M"  File: lispref.info, Node: Help Functions, Next: Obsoleteness, Prev: Describing Characters, Up: Documentation Help Functions ============== XEmacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix `C-h', or on some keyboards, `help'. For more information about them, see *Note Help: (emacs)Help. Here we describe some program-level interfaces to the same information. - Command: apropos REGEXP &optional DO-ALL PREDICATE This function finds all symbols whose names contain a match for the regular expression REGEXP, and returns a list of them (*note Regular Expressions::.). It also displays the symbols in a buffer named `*Help*', each with a one-line description. If DO-ALL is non-`nil', then `apropos' also shows key bindings for the functions that are found. If PREDICATE is non-`nil', it should be a function to be called on each symbol that has matched REGEXP. Only symbols for which PREDICATE returns a non-`nil' value are listed or displayed. In the first of the following examples, `apropos' finds all the symbols with names containing `exec'. In the second example, it finds and returns only those symbols that are also commands. (We don't show the output that results in the `*Help*' buffer.) (apropos "exec") => (Buffer-menu-execute command-execute exec-directory exec-path execute-extended-command execute-kbd-macro executing-kbd-macro executing-macro) (apropos "exec" nil 'commandp) => (Buffer-menu-execute execute-extended-command) `apropos' is used by various user-level commands, such as `C-h a' (`hyper-apropos'), a graphical front-end to `apropos'; and `C-h A' (`command-apropos'), which does an apropos over only those functions which are user commands. `command-apropos' calls `apropos', specifying a PREDICATE to restrict the output to symbols that are commands. The call to `apropos' looks like this: (apropos string t 'commandp) - Variable: help-map The value of this variable is a local keymap for characters following the Help key, `C-h'. - Prefix Command: help-command This symbol is not a function; its function definition is actually the keymap known as `help-map'. It is defined in `help.el' as follows: (define-key global-map "\C-h" 'help-command) (fset 'help-command help-map) - Function: print-help-return-message &optional FUNCTION This function builds a string that explains how to restore the previous state of the windows after a help command. After building the message, it applies FUNCTION to it if FUNCTION is non-`nil'. Otherwise it calls `message' to display it in the echo area. This function expects to be called inside a `with-output-to-temp-buffer' special form, and expects `standard-output' to have the value bound by that special form. For an example of its use, see the long example in *Note Accessing Documentation::. - Variable: help-char The value of this variable is the help character--the character that XEmacs recognizes as meaning Help. By default, it is the character `?\^H' (ASCII 8), which is `C-h'. When XEmacs reads this character, if `help-form' is non-`nil' Lisp expression, it evaluates that expression, and displays the result in a window if it is a string. `help-char' can be a character or a key description such as `help' or `(meta h)'. Usually the value of `help-form''s value is `nil'. Then the help character has no special meaning at the level of command input, and it becomes part of a key sequence in the normal way. The standard key binding of `C-h' is a prefix key for several general-purpose help features. The help character is special after prefix keys, too. If it has no binding as a subcommand of the prefix key, it runs `describe-prefix-bindings', which displays a list of all the subcommands of the prefix key. - Variable: help-form If this variable is non-`nil', its value is a form to evaluate whenever the character `help-char' is read. If evaluating the form produces a string, that string is displayed. A command that calls `next-command-event' or `next-event' probably should bind `help-form' to a non-`nil' expression while it does input. (The exception is when `C-h' is meaningful input.) Evaluating this expression should result in a string that explains what the input is for and how to enter it properly. Entry to the minibuffer binds this variable to the value of `minibuffer-help-form' (*note Minibuffer Misc::.). - Variable: prefix-help-command This variable holds a function to print help for a prefix character. The function is called when the user types a prefix key followed by the help character, and the help character has no binding after that prefix. The variable's default value is `describe-prefix-bindings'. - Function: describe-prefix-bindings This function calls `describe-bindings' to display a list of all the subcommands of the prefix key of the most recent key sequence. The prefix described consists of all but the last event of that key sequence. (The last event is, presumably, the help character.) The following two functions are found in the library `helper'. They are for modes that want to provide help without relinquishing control, such as the "electric" modes. You must load that library with `(require 'helper)' in order to use them. Their names begin with `Helper' to distinguish them from the ordinary help functions. - Command: Helper-describe-bindings This command pops up a window displaying a help buffer containing a listing of all of the key bindings from both the local and global keymaps. It works by calling `describe-bindings'. - Command: Helper-help This command provides help for the current mode. It prompts the user in the minibuffer with the message `Help (Type ? for further options)', and then provides assistance in finding out what the key bindings are, and what the mode is intended for. It returns `nil'. This can be customized by changing the map `Helper-help-map'.  File: lispref.info, Node: Obsoleteness, Prev: Help Functions, Up: Documentation Obsoleteness ============ As you add functionality to a package, you may at times want to replace an older function with a new one. To preserve compatibility with existing code, the older function needs to still exist; but users of that function should be told to use the newer one instead. XEmacs Lisp lets you mark a function or variable as "obsolete", and indicate what should be used instead. - Function: make-obsolete FUNCTION NEW This function indicates that FUNCTION is an obsolete function, and the function NEW should be used instead. The byte compiler will issue a warning to this effect when it encounters a usage of the older function, and the help system will also note this in the function's documentation. NEW can also be a string (if there is not a single function with the same functionality any more), and should be a descriptive statement, such as "use FOO or BAR instead" or "this function is unnecessary". - Function: make-obsolete-variable VARIABLE NEW This is like `make-obsolete' but is for variables instead of functions. - Function: define-obsolete-function-alias OLDFUN NEWFUN This function combines `make-obsolete' and `define-function', declaring OLDFUN to be an obsolete variant of NEWFUN and defining OLDFUN as an alias for NEWFUN. - Function: define-obsolete-variable-alias OLDVAR NEWVAR This is like `define-obsolete-function-alias' but for variables. Note that you should not normally put obsoleteness information explicitly in a function or variable's doc string. The obsoleteness information that you specify using the above functions will be displayed whenever the doc string is displayed, and by adding it explicitly the result is redundancy. Also, if an obsolete function is substantially the same as a newer one but is not actually an alias, you should consider omitting the doc string entirely (use a null string `""' as the doc string). That way, the user is told about the obsoleteness and is forced to look at the documentation of the new function, making it more likely that he will use the new function. - Function: function-obsoleteness-doc FUNCTION If FUNCTION is obsolete, this function returns a string describing this. This is the message that is printed out during byte compilation or in the function's documentation. If FUNCTION is not obsolete, `nil' is returned. - Function: variable-obsoleteness-doc VARIABLE This is like `function-obsoleteness-doc' but for variables. The obsoleteness information is stored internally by putting a property `byte-obsolete-info' (for functions) or `byte-obsolete-variable' (for variables) on the symbol that specifies the obsolete function or variable. For more information, see the implementation of `make-obsolete' and `make-obsolete-variable' in `lisp/bytecomp/bytecomp-runtime.el'.  File: lispref.info, Node: Files, Next: Backups and Auto-Saving, Prev: Documentation, Up: Top Files ***** In XEmacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of XEmacs Lisp, but a few others are described in *Note Buffers::, and those related to backups and auto-saving are described in *Note Backups and Auto-Saving::. Many of the file functions take one or more arguments that are file names. A file name is actually a string. Most of these functions expand file name arguments using `expand-file-name', so that `~' is handled correctly, as are relative file names (including `../'). These functions don't recognize environment variable substitutions such as `$HOME'. *Note File Name Expansion::. * Menu: * Visiting Files:: Reading files into Emacs buffers for editing. * Saving Buffers:: Writing changed buffers back into files. * Reading from Files:: Reading files into buffers without visiting. * Writing to Files:: Writing new files from parts of buffers. * File Locks:: Locking and unlocking files, to prevent simultaneous editing by two people. * Information about Files:: Testing existence, accessibility, size of files. * Changing File Attributes:: Renaming files, changing protection, etc. * File Names:: Decomposing and expanding file names. * Contents of Directories:: Getting a list of the files in a directory. * Create/Delete Dirs:: Creating and Deleting Directories. * Magic File Names:: Defining "magic" special handling for certain file names. * Partial Files:: Treating a section of a buffer as a file. * Format Conversion:: Conversion to and from various file formats. * Files and MS-DOS:: Distinguishing text and binary files on MS-DOS.  File: lispref.info, Node: Visiting Files, Next: Saving Buffers, Up: Files Visiting Files ============== Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is "visiting" that file, and call the file "the visited file" of the buffer. A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of XEmacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must "save" the buffer, which means copying the altered buffer contents back into the file. In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, "I am editing a file," rather than, "I am editing a buffer that I will soon save as a file of the same name." Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind. * Menu: * Visiting Functions:: The usual interface functions for visiting. * Subroutines of Visiting:: Lower-level subroutines that they use.  File: lispref.info, Node: Visiting Functions, Next: Subroutines of Visiting, Up: Visiting Files Functions for Visiting Files ---------------------------- This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with `find-' rather than `visit-'. *Note Buffer File Name::, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name. In a Lisp program, if you want to look at the contents of a file but not alter it, the fastest way is to use `insert-file-contents' in a temporary buffer. Visiting the file is not necessary and takes longer. *Note Reading from Files::. - Command: find-file FILENAME This command selects a buffer visiting the file FILENAME, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer. The body of the `find-file' function is very simple and looks like this: (switch-to-buffer (find-file-noselect filename)) (See `switch-to-buffer' in *Note Displaying Buffers::.) When `find-file' is called interactively, it prompts for FILENAME in the minibuffer. - Function: find-file-noselect FILENAME &optional NOWARN This function is the guts of all the file-visiting functions. It finds or creates a buffer visiting the file FILENAME, and returns it. It uses an existing buffer if there is one, and otherwise creates a new buffer and reads the file into it. You may make the buffer current or display it in a window if you wish, but this function does not do so. When `find-file-noselect' uses an existing buffer, it first verifies that the file has not changed since it was last visited or saved in that buffer. If the file has changed, then this function asks the user whether to reread the changed file. If the user says `yes', any changes previously made in the buffer are lost. If `find-file-noselect' needs to create a buffer, and there is no file named FILENAME, it displays the message `New file' in the echo area, and leaves the buffer empty. If NO-WARN is non-`nil', various warnings that XEmacs normally gives (e.g. if another buffer is already visiting FILENAME but FILENAME has been removed from disk since that buffer was created) are suppressed. The `find-file-noselect' function calls `after-find-file' after reading the file (*note Subroutines of Visiting::.). That function sets the buffer major mode, parses local variables, warns the user if there exists an auto-save file more recent than the file just visited, and finishes by running the functions in `find-file-hooks'. The `find-file-noselect' function returns the buffer that is visiting the file FILENAME. (find-file-noselect "/etc/fstab") => # - Command: find-file-other-window FILENAME This command selects a buffer visiting the file FILENAME, but does so in a window other than the selected window. It may use another existing window or split a window; see *Note Displaying Buffers::. When this command is called interactively, it prompts for FILENAME. - Command: find-file-read-only FILENAME This command selects a buffer visiting the file FILENAME, like `find-file', but it marks the buffer as read-only. *Note Read Only Buffers::, for related functions and variables. When this command is called interactively, it prompts for FILENAME. - Command: view-file FILENAME This command visits FILENAME in View mode, and displays it in a recursive edit, returning to the previous buffer when done. View mode is a mode that allows you to skim rapidly through the file but does not let you modify it. Entering View mode runs the normal hook `view-mode-hook'. *Note Hooks::. When `view-file' is called interactively, it prompts for FILENAME. - Variable: find-file-hooks The value of this variable is a list of functions to be called after a file is visited. The file's local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run. This variable works just like a normal hook, but we think that renaming it would not be advisable. - Variable: find-file-not-found-hooks The value of this variable is a list of functions to be called when `find-file' or `find-file-noselect' is passed a nonexistent file name. `find-file-noselect' calls these functions as soon as it detects a nonexistent file. It calls them in the order of the list, until one of them returns non-`nil'. `buffer-file-name' is already set up. This is not a normal hook because the values of the functions are used and they may not all be called.  File: lispref.info, Node: Subroutines of Visiting, Prev: Visiting Functions, Up: Visiting Files Subroutines of Visiting ----------------------- The `find-file-noselect' function uses the `create-file-buffer' and `after-find-file' functions as subroutines. Sometimes it is useful to call them directly. - Function: create-file-buffer FILENAME This function creates a suitably named buffer for visiting FILENAME, and returns it. It uses FILENAME (sans directory) as the name if that name is free; otherwise, it appends a string such as `<2>' to get an unused name. See also *Note Creating Buffers::. *Please note:* `create-file-buffer' does *not* associate the new buffer with a file and does not select the buffer. It also does not use the default major mode. (create-file-buffer "foo") => # (create-file-buffer "foo") => #> (create-file-buffer "foo") => #> This function is used by `find-file-noselect'. It uses `generate-new-buffer' (*note Creating Buffers::.). - Function: after-find-file &optional ERROR WARN NOAUTO This function sets the buffer major mode, and parses local variables (*note Auto Major Mode::.). It is called by `find-file-noselect' and by the default revert function (*note Reverting::.). If reading the file got an error because the file does not exist, but its directory does exist, the caller should pass a non-`nil' value for ERROR. In that case, `after-find-file' issues a warning: `(New File)'. For more serious errors, the caller should usually not call `after-find-file'. If WARN is non-`nil', then this function issues a warning if an auto-save file exists and is more recent than the visited file. If NOAUTO is non-`nil', then this function does not turn on auto-save mode; otherwise, it does. The last thing `after-find-file' does is call all the functions in `find-file-hooks'.  File: lispref.info, Node: Saving Buffers, Next: Reading from Files, Prev: Visiting Files, Up: Files Saving Buffers ============== When you edit a file in XEmacs, you are actually working on a buffer that is visiting that file--that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you "save" the buffer, which means copying the contents of the buffer into the file. - Command: save-buffer &optional BACKUP-OPTION This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing. `save-buffer' is responsible for making backup files. Normally, BACKUP-OPTION is `nil', and `save-buffer' makes a backup file only if this is the first save since visiting the file. Other values for BACKUP-OPTION request the making of backup files in other circumstances: * With an argument of 4 or 64, reflecting 1 or 3 `C-u''s, the `save-buffer' function marks this version of the file to be backed up when the buffer is next saved. * With an argument of 16 or 64, reflecting 2 or 3 `C-u''s, the `save-buffer' function unconditionally backs up the previous version of the file before saving it. - Command: save-some-buffers &optional SAVE-SILENTLY-P EXITING This command saves some modified file-visiting buffers. Normally it asks the user about each buffer. But if SAVE-SILENTLY-P is non-`nil', it saves all the file-visiting buffers without querying the user. The optional EXITING argument, if non-`nil', requests this function to offer also to save certain other buffers that are not visiting files. These are buffers that have a non-`nil' local value of `buffer-offer-save'. (A user who says yes to saving one of these is asked to specify a file name to use.) The `save-buffers-kill-emacs' function passes a non-`nil' value for this argument. - Variable: buffer-offer-save When this variable is non-`nil' in a buffer, XEmacs offers to save the buffer on exit even if the buffer is not visiting a file. The variable is automatically local in all buffers. Normally, Mail mode (used for editing outgoing mail) sets this to `t'. - Command: write-file FILENAME This function writes the current buffer into file FILENAME, makes the buffer visit that file, and marks it not modified. Then it renames the buffer based on FILENAME, appending a string like `<2>' if necessary to make a unique buffer name. It does most of this work by calling `set-visited-file-name' and `save-buffer'. - Variable: write-file-hooks The value of this variable is a list of functions to be called before writing out a buffer to its visited file. If one of them returns non-`nil', the file is considered already written and the rest of the functions are not called, nor is the usual code for writing the file executed. If a function in `write-file-hooks' returns non-`nil', it is responsible for making a backup file (if that is appropriate). To do so, execute the following code: (or buffer-backed-up (backup-buffer)) You might wish to save the file modes value returned by `backup-buffer' and use that to set the mode bits of the file that you write. This is what `save-buffer' normally does. Even though this is not a normal hook, you can use `add-hook' and `remove-hook' to manipulate the list. *Note Hooks::. - Variable: local-write-file-hooks This works just like `write-file-hooks', but it is intended to be made local to particular buffers. It's not a good idea to make `write-file-hooks' local to a buffer--use this variable instead. The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read "file" contents in special ways, and set up hooks to save the data in a corresponding way. - Variable: write-contents-hooks This works just like `write-file-hooks', but it is intended for hooks that pertain to the contents of the file, as opposed to hooks that pertain to where the file came from. Such hooks are usually set up by major modes, as buffer-local bindings for this variable. Switching to a new major mode always resets this variable. - Variable: after-save-hook This normal hook runs after a buffer has been saved in its visited file. - Variable: file-precious-flag If this variable is non-`nil', then `save-buffer' protects against I/O errors while saving by writing the new file to a temporary name instead of the name it is supposed to have, and then renaming it to the intended name after it is clear there are no errors. This procedure prevents problems such as a lack of disk space from resulting in an invalid file. As a side effect, backups are necessarily made by copying. *Note Rename or Copy::. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names. Some modes set this variable non-`nil' locally in particular buffers. - User Option: require-final-newline This variable determines whether files may be written out that do *not* end with a newline. If the value of the variable is `t', then `save-buffer' silently adds a newline at the end of the file whenever the buffer being saved does not already end in one. If the value of the variable is non-`nil', but not `t', then `save-buffer' asks the user whether to add a newline each time the case arises. If the value of the variable is `nil', then `save-buffer' doesn't add newlines at all. `nil' is the default value, but a few major modes set it to `t' in particular buffers.  File: lispref.info, Node: Reading from Files, Next: Writing to Files, Prev: Saving Buffers, Up: Files Reading from Files ================== You can copy a file from the disk and insert it into a buffer using the `insert-file-contents' function. Don't use the user-level command `insert-file' in a Lisp program, as that sets the mark. - Function: insert-file-contents FILENAME &optional VISIT BEG END REPLACE This function inserts the contents of file FILENAME into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if FILENAME is not the name of a file that can be read. The function `insert-file-contents' checks the file contents against the defined file formats, and converts the file contents if appropriate. *Note Format Conversion::. It also calls the functions in the list `after-insert-file-functions'; see *Note Saving Properties::. If VISIT is non-`nil', this function additionally marks the buffer as unmodified and sets up various fields in the buffer so that it is visiting the file FILENAME: these include the buffer's visited file name and its last save file modtime. This feature is used by `find-file-noselect' and you probably should not use it yourself. If BEG and END are non-`nil', they should be integers specifying the portion of the file to insert. In this case, VISIT must be `nil'. For example, (insert-file-contents filename nil 0 500) inserts the first 500 characters of a file. If the argument REPLACE is non-`nil', it means to replace the contents of the buffer (actually, just the accessible portion) with the contents of the file. This is better than simply deleting the buffer contents and inserting the whole file, because (1) it preserves some marker positions and (2) it puts less data in the undo list. If you want to pass a file name to another process so that another program can read the file, use the function `file-local-copy'; see *Note Magic File Names::.  File: lispref.info, Node: Writing to Files, Next: File Locks, Prev: Reading from Files, Up: Files Writing to Files ================ You can write the contents of a buffer, or part of a buffer, directly to a file on disk using the `append-to-file' and `write-region' functions. Don't use these functions to write to files that are being visited; that could cause confusion in the mechanisms for visiting. - Command: append-to-file START END FILENAME This function appends the contents of the region delimited by START and END in the current buffer to the end of file FILENAME. If that file does not exist, it is created. If that file exists it is overwritten. This function returns `nil'. An error is signaled if FILENAME specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created. - Command: write-region START END FILENAME &optional APPEND VISIT This function writes the region delimited by START and END in the current buffer into the file specified by FILENAME. If START is a string, then `write-region' writes or appends that string, rather than text from the buffer. If APPEND is non-`nil', then the specified text is appended to the existing file contents (if any). If VISIT is `t', then XEmacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to FILENAME's modtime, and marks the buffer as not modified. This feature is used by `save-buffer', but you probably should not use it yourself. If VISIT is a string, it specifies the file name to visit. This way, you can write the data to one file (FILENAME) while recording the buffer as visiting another file (VISIT). The argument VISIT is used in the echo area message and also for file locking; VISIT is stored in `buffer-file-name'. This feature is used to implement `file-precious-flag'; don't use it yourself unless you really know what you're doing. The function `write-region' converts the data which it writes to the appropriate file formats specified by `buffer-file-format'. *Note Format Conversion::. It also calls the functions in the list `write-region-annotate-functions'; see *Note Saving Properties::. Normally, `write-region' displays a message `Wrote file FILENAME' in the echo area. If VISIT is neither `t' nor `nil' nor a string, then this message is inhibited. This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.  File: lispref.info, Node: File Locks, Next: Information about Files, Prev: Writing to Files, Up: Files File Locks ========== When two users edit the same file at the same time, they are likely to interfere with each other. XEmacs tries to prevent this situation from arising by recording a "file lock" when a file is being modified. XEmacs can then detect the first attempt to modify a buffer visiting a file that is locked by another XEmacs process, and ask the user what to do. File locks do not work properly when multiple machines can share file systems, such as with NFS. Perhaps a better file locking system will be implemented in the future. When file locks do not work, it is possible for two users to make changes simultaneously, but XEmacs can still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see *Note Modification Time::. - Function: file-locked-p &optional FILENAME This function returns `nil' if the file FILENAME is not locked by this XEmacs process. It returns `t' if it is locked by this XEmacs, and it returns the name of the user who has locked it if it is locked by someone else. (file-locked-p "foo") => nil - Function: lock-buffer &optional FILENAME This function locks the file FILENAME, if the current buffer is modified. The argument FILENAME defaults to the current buffer's visited file. Nothing is done if the current buffer is not visiting a file, or is not modified. - Function: unlock-buffer This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file. - Function: ask-user-about-lock FILE OTHER-USER This function is called when the user tries to modify FILE, but it is locked by another user named OTHER-USER. The value it returns determines what happens next: * A value of `t' says to grab the lock on the file. Then this user may edit the file and OTHER-USER loses the lock. * A value of `nil' says to ignore the lock and let this user edit the file anyway. * This function may instead signal a `file-locked' error, in which case the change that the user was about to make does not take place. The error message for this error looks like this: error--> File is locked: FILE OTHER-USER where `file' is the name of the file and OTHER-USER is the name of the user who has locked the file. The default definition of this function asks the user to choose what to do. If you wish, you can replace the `ask-user-about-lock' function with your own version that decides in another way. The code for its usual definition is in `userlock.el'.  File: lispref.info, Node: Information about Files, Next: Changing File Attributes, Prev: File Locks, Up: Files Information about Files ======================= The functions described in this section all operate on strings that designate file names. All the functions have names that begin with the word `file'. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted. * Menu: * Testing Accessibility:: Is a given file readable? Writable? * Kinds of Files:: Is it a directory? A symbolic link? * Truenames:: Eliminating symbolic links from a file name. * File Attributes:: How large is it? Any other names? Etc.