This is Info file elisp, produced by Makeinfo version 1.68 from the input file elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This version is the edition 2.5 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 20.3 Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998 Free Software Foundation, Inc. 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: elisp, Node: Subroutines of Visiting, Prev: Visiting Functions, Up: Visiting Files Subroutines of Visiting ----------------------- The `find-file-noselect' function uses two important subroutines which are sometimes useful in user Lisp code: `create-file-buffer' and `after-find-file'. This section explains how to use them. - 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 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. The last thing `after-find-file' does is call all the functions in the list `find-file-hooks'.  File: elisp, Node: Saving Buffers, Next: Reading from Files, Prev: Visiting Files, Up: Files 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 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' buffer-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. - 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' (*note Buffer File Name::.) and `save-buffer'. Saving a buffer runs several hooks. It also performs format conversion (*note Format Conversion::.), and may save text properties in "annotations" (*note Saving Properties::.). - 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. The hook functions in `write-file-hooks' are also responsible for encoding the data (if desired): they must choose a suitable coding system (*note Lisp and Coding Systems::.), perform the encoding (*note Explicit Encoding::.), and set `last-coding-system-used' to the coding system that was used (*note Encoding and I/O::.). Do not make this variable buffer-local. To set up buffer-specific hook functions, use `write-contents-hooks' instead. 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 buffer-local in particular buffers, and used for hooks that pertain to the file name or the way the buffer contents were obtained. 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. This variable automatically becomes buffer-local whenever it is set; switching to a new major mode always resets this variable. When you use `add-hooks' to add an element to this hook, you should *not* specify a non-`nil' LOCAL argument, since this variable is used *only* buffer-locally. - Variable: after-save-hook This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache 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 give this variable a non-`nil' buffer-local value 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. See also the function `set-visited-file-name' (*note Buffer File Name::.).  File: elisp, 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. It is possible to read a special file (such as a FIFO or an I/O device) with `insert-file-contents', as long as REPLACE and VISIT are `nil'. - Function: insert-file-contents-literally FILENAME &optional VISIT BEG END REPLACE This function works like `insert-file-contents' except that it does not do format decoding (*note Format Conversion::.), does not do character code conversion (*note Coding Systems::.), does not run `find-file-hooks', does not perform automatic uncompression, and so on. 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: elisp, 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. 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 CONFIRM 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 CONFIRM is non-`nil', then `write-region' asks for confirmation if FILENAME names an existing file. If VISIT is `t', then Emacs 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 the message `Wrote 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. - Macro: with-temp-file FILE BODY... The `with-temp-file' macro evaluates the BODY forms with a temporary buffer as the current buffer; then, at the end, it writes the buffer contents into file FILE. It kills the temporary buffer when finished, restoring the buffer that was current before the `with-temp-file' form. Then it returns the value of the last form in BODY. The current buffer is restored even in case of an abnormal exit via `throw' or error (*note Nonlocal Exits::.). See also `with-temp-buffer' in *Note Current Buffer::.  File: elisp, 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. Emacs tries to prevent this situation from arising by recording a "file lock" when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do. File locks are not completely reliable when multiple machines can share file systems. When file locks do not work, it is possible for two users to make changes simultaneously, but Emacs 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 FILENAME This function returns `nil' if the file FILENAME is not locked. It returns `t' if it is locked by this Emacs process, and it returns the name of the user who has locked it if it is locked by some other job. (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 default definition of this function asks the user to say what to do. The value this function returns determines what Emacs does 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. If you wish, you can replace the `ask-user-about-lock' function with your own version that makes the decision in another way. The code for its usual definition is in `userlock.el'.  File: elisp, Node: Information about Files, Next: Changing Files, 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.  File: elisp, Node: Testing Accessibility, Next: Kinds of Files, Up: Information about Files Testing Accessibility --------------------- These functions test for permission to access a file in specific ways. - Function: file-exists-p FILENAME This function returns `t' if a file named FILENAME appears to exist. This does not mean you can necessarily read the file, only that you can find out its attributes. (On Unix, this is true if the file exists and you have execute permission on the containing directories, regardless of the protection of the file itself.) If the file does not exist, or if fascist access control policies prevent you from finding the attributes of the file, this function returns `nil'. - Function: file-readable-p FILENAME This function returns `t' if a file named FILENAME exists and you can read it. It returns `nil' otherwise. (file-readable-p "files.texi") => t (file-exists-p "/usr/spool/mqueue") => t (file-readable-p "/usr/spool/mqueue") => nil - Function: file-executable-p FILENAME This function returns `t' if a file named FILENAME exists and you can execute it. It returns `nil' otherwise. If the file is a directory, execute permission means you can check the existence and attributes of files inside the directory, and open those files if their modes permit. - Function: file-writable-p FILENAME This function returns `t' if the file FILENAME can be written or created by you, and `nil' otherwise. A file is writable if the file exists and you can write it. It is creatable if it does not exist, but the specified directory does exist and you can write in that directory. In the third example below, `foo' is not writable because the parent directory does not exist, even though the user could create such a directory. (file-writable-p "~/foo") => t (file-writable-p "/foo") => nil (file-writable-p "~/no-such-dir/foo") => nil - Function: file-accessible-directory-p DIRNAME This function returns `t' if you have permission to open existing files in the directory whose name as a file is DIRNAME; otherwise (or if there is no such directory), it returns `nil'. The value of DIRNAME may be either a directory name or the file name of a file which is a directory. Example: after the following, (file-accessible-directory-p "/foo") => nil we can deduce that any attempt to read a file in `/foo/' will give an error. - Function: access-file FILENAME STRING This function opens file FILENAME for reading, then closes it and returns `nil'. However, if the open fails, it signals an error using STRING as the error message text. - Function: file-ownership-preserved-p FILENAME This function returns `t' if deleting the file FILENAME and then creating it anew would keep the file's owner unchanged. - Function: file-newer-than-file-p FILENAME1 FILENAME2 This function returns `t' if the file FILENAME1 is newer than file FILENAME2. If FILENAME1 does not exist, it returns `nil'. If FILENAME2 does not exist, it returns `t'. In the following example, assume that the file `aug-19' was written on the 19th, `aug-20' was written on the 20th, and the file `no-file' doesn't exist at all. (file-newer-than-file-p "aug-19" "aug-20") => nil (file-newer-than-file-p "aug-20" "aug-19") => t (file-newer-than-file-p "aug-19" "no-file") => t (file-newer-than-file-p "no-file" "aug-19") => nil You can use `file-attributes' to get a file's last modification time as a list of two numbers. *Note File Attributes::.  File: elisp, Node: Kinds of Files, Next: Truenames, Prev: Testing Accessibility, Up: Information about Files Distinguishing Kinds of Files ----------------------------- This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files. - Function: file-symlink-p FILENAME If the file FILENAME is a symbolic link, the `file-symlink-p' function returns the file name to which it is linked. This may be the name of a text file, a directory, or even another symbolic link, or it may be a nonexistent file name. If the file FILENAME is not a symbolic link (or there is no such file), `file-symlink-p' returns `nil'. (file-symlink-p "foo") => nil (file-symlink-p "sym-link") => "foo" (file-symlink-p "sym-link2") => "sym-link" (file-symlink-p "/bin") => "/pub/bin" - Function: file-directory-p FILENAME This function returns `t' if FILENAME is the name of an existing directory, `nil' otherwise. (file-directory-p "~rms") => t (file-directory-p "~rms/lewis/files.texi") => nil (file-directory-p "~rms/lewis/no-such-file") => nil (file-directory-p "$HOME") => nil (file-directory-p (substitute-in-file-name "$HOME")) => t - Function: file-regular-p FILENAME This function returns `t' if the file FILENAME exists and is a regular file (not a directory, symbolic link, named pipe, terminal, or other I/O device).  File: elisp, Node: Truenames, Next: File Attributes, Prev: Kinds of Files, Up: Information about Files Truenames --------- The "truename" of a file is the name that you get by following symbolic links until none remain, then simplifying away `.' and `..' appearing as components. Strictly speaking, a file need not have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation. - Function: file-truename FILENAME The function `file-truename' returns the true name of the file FILENAME. This is the name that you get by following symbolic links until none remain. The argument must be an absolute file name. *Note Buffer File Name::, for related information.  File: elisp, Node: File Attributes, Prev: Truenames, Up: Information about Files Other Information about Files ----------------------------- This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification. - Function: file-modes FILENAME This function returns the mode bits of FILENAME, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second-lowest-order bit is 1, then the file is writable by all users, etc. The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the SUID bit is set for both others and group, and that the sticky bit is set. (file-modes "~/junk/diffs") => 492 ; Decimal integer. (format "%o" 492) => "754" ; Convert to octal. (set-file-modes "~/junk/diffs" 438) => nil (format "%o" 438) => "666" ; Convert to octal. % ls -l diffs -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs - Function: file-nlinks FILENAME This functions returns the number of names (i.e., hard links) that file FILENAME has. If the file does not exist, then this function returns `nil'. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to. % ls -l foo* -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 (file-nlinks "foo") => 2 (file-nlinks "doesnt-exist") => nil - Function: file-attributes FILENAME This function returns a list of attributes of file FILENAME. If the specified file cannot be opened, it returns `nil'. The elements of the list, in order, are: 0. `t' for a directory, a string for a symbolic link (the name linked to), or `nil' for a text file. 1. The number of names the file has. Alternate names, also known as hard links, can be created by using the `add-name-to-file' function (*note Changing Files::.). 2. The file's UID. 3. The file's GID. 4. The time of last access, as a list of two integers. The first integer has the high-order 16 bits of time, the second has the low 16 bits. (This is similar to the value of `current-time'; see *Note Time of Day::.) 5. The time of last modification as a list of two integers (as above). 6. The time of last status change as a list of two integers (as above). 7. The size of the file in bytes. 8. The file's modes, as a string of ten letters or dashes, as in `ls -l'. 9. `t' if the file's GID would change if file were deleted and recreated; `nil' otherwise. 10. The file's inode number. If possible, this is an integer. If the inode number is too large to be represented as an integer in Emacs Lisp, then the value has the form `(HIGH . LOW)', where LOW holds the low 16 bits. 11. The file system number of the file system that the file is in. This element and the file's inode number together give enough information to distinguish any two files on the system--no two files can have the same values for both of these numbers. For example, here are the file attributes for `files.texi': (file-attributes "files.texi") => (nil 1 2235 75 (8489 20284) (8489 20284) (8489 20285) 14906 "-rw-rw-rw-" nil 129500 -32252) and here is how the result is interpreted: `nil' is neither a directory nor a symbolic link. `1' has only one name (the name `files.texi' in the current default directory). `2235' is owned by the user with UID 2235. `75' is in the group with GID 75. `(8489 20284)' was last accessed on Aug 19 00:09. `(8489 20284)' was last modified on Aug 19 00:09. `(8489 20285)' last had its inode changed on Aug 19 00:09. `14906' is 14906 characters long. `"-rw-rw-rw-"' has a mode of read and write access for the owner, group, and world. `nil' would retain the same GID if it were recreated. `129500' has an inode number of 129500. `-32252' is on file system number -32252.  File: elisp, Node: Changing Files, Next: File Names, Prev: Information about Files, Up: Files Changing File Names and Attributes ================================== The functions in this section rename, copy, delete, link, and set the modes of files. In the functions that have an argument NEWNAME, if a file by the name of NEWNAME already exists, the actions taken depend on the value of the argument OK-IF-ALREADY-EXISTS: * Signal a `file-already-exists' error if OK-IF-ALREADY-EXISTS is `nil'. * Request confirmation if OK-IF-ALREADY-EXISTS is a number. * Replace the old file without confirmation if OK-IF-ALREADY-EXISTS is any other value. - Function: add-name-to-file OLDNAME NEWNAME &optional OK-IF-ALREADY-EXISTS This function gives the file named OLDNAME the additional name NEWNAME. This means that NEWNAME becomes a new "hard link" to OLDNAME. In the first part of the following example, we list two files, `foo' and `foo3'. % ls -li fo* 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Now we create a hard link, by calling `add-name-to-file', then list the files again. This shows two names for one file, `foo' and `foo2'. (add-name-to-file "foo" "foo2") => nil % ls -li fo* 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Finally, we evaluate the following: (add-name-to-file "foo" "foo3" t) and list the files again. Now there are three names for one file: `foo', `foo2', and `foo3'. The old contents of `foo3' are lost. (add-name-to-file "foo1" "foo3") => nil % ls -li fo* 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3 This function is meaningless on operating systems where multiple names for one file are not allowed. See also `file-nlinks' in *Note File Attributes::. - Command: rename-file FILENAME NEWNAME &optional OK-IF-ALREADY-EXISTS This command renames the file FILENAME as NEWNAME. If FILENAME has additional names aside from FILENAME, it continues to have those names. In fact, adding the name NEWNAME with `add-name-to-file' and then deleting FILENAME has the same effect as renaming, aside from momentary intermediate states. In an interactive call, this function prompts for FILENAME and NEWNAME in the minibuffer; also, it requests confirmation if NEWNAME already exists. - Command: copy-file OLDNAME NEWNAME &optional OK-IF-EXISTS TIME This command copies the file OLDNAME to NEWNAME. An error is signaled if OLDNAME does not exist. If TIME is non-`nil', then this function gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) If setting the time gets an error, `copy-file' signals a `file-date-error' error. In an interactive call, this function prompts for FILENAME and NEWNAME in the minibuffer; also, it requests confirmation if NEWNAME already exists. - Command: delete-file FILENAME This command deletes the file FILENAME, like the shell command `rm FILENAME'. If the file has multiple names, it continues to exist under the other names. A suitable kind of `file-error' error is signaled if the file does not exist, or is not deletable. (On Unix, a file is deletable if its directory is writable.) See also `delete-directory' in *Note Create/Delete Dirs::. - Command: make-symbolic-link FILENAME NEWNAME &optional OK-IF-EXISTS This command makes a symbolic link to FILENAME, named NEWNAME. This is like the shell command `ln -s FILENAME NEWNAME'. In an interactive call, this function prompts for FILENAME and NEWNAME in the minibuffer; also, it requests confirmation if NEWNAME already exists. - Function: define-logical-name VARNAME STRING This function defines the logical name NAME to have the value STRING. It is available only on VMS. - Function: set-file-modes FILENAME MODE This function sets mode bits of FILENAME to MODE (which must be an integer). Only the low 12 bits of MODE are used. - Function: set-default-file-modes MODE This function sets the default file protection for new files created by Emacs and its subprocesses. Every file created with Emacs initially has this protection. On Unix, the default protection is the bitwise complement of the "umask" value. The argument MODE must be an integer. On most systems, only the low 9 bits of MODE are meaningful. Saving a modified version of an existing file does not count as creating the file; it does not change the file's mode, and does not use the default file protection. - Function: default-file-modes This function returns the current default protection value. On MS-DOS, there is no such thing as an "executable" file mode bit. So Emacs considers a file executable if its name ends in `.com', `.bat' or `.exe'. This is reflected in the values returned by `file-modes' and `file-attributes'.  File: elisp, Node: File Names, Next: Contents of Directories, Prev: Changing Files, Up: Files File Names ========== Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument. In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names. The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory. On VMS, all these functions understand both VMS file-name syntax and Unix syntax. This is so that all the standard Lisp libraries can specify file names in Unix syntax and work properly on VMS without change. On MS-DOS and MS-Windows, these functions understand MS-DOS or MS-Windows file-name syntax as well as Unix syntax. * Menu: * File Name Components:: The directory part of a file name, and the rest. * Directory Names:: A directory's name as a directory is different from its name as a file. * Relative File Names:: Some file names are relative to a current directory. * File Name Expansion:: Converting relative file names to absolute ones. * Unique File Names:: Generating names for temporary files. * File Name Completion:: Finding the completions for a given file name. * Standard File Names:: If your package uses a fixed file name, how to handle various operating systems simply.  File: elisp, Node: File Name Components, Next: Directory Names, Up: File Names File Name Components -------------------- The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the "directory name" part, and the "nondirectory" part (or "file name within the directory"). Either part may be empty. Concatenating these two parts reproduces the original file name. On Unix, the directory part is everything up to and including the last slash; the nondirectory part is the rest. The rules in VMS syntax are complicated. For some purposes, the nondirectory part is further subdivided into the name proper and the "version number". On Unix, only backup files have version numbers in their names. On VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number, so that version numbers in Emacs are found mostly in directory lists. - Function: file-name-directory FILENAME This function returns the directory part of FILENAME (or `nil' if FILENAME does not include a directory part). On Unix, the function returns a string ending in a slash. On VMS, it returns a string ending in one of the three characters `:', `]', or `>'. (file-name-directory "lewis/foo") ; Unix example => "lewis/" (file-name-directory "foo") ; Unix example => nil (file-name-directory "[X]FOO.TMP") ; VMS example => "[X]" - Function: file-name-nondirectory FILENAME This function returns the nondirectory part of FILENAME. (file-name-nondirectory "lewis/foo") => "foo" (file-name-nondirectory "foo") => "foo" ;; The following example is accurate only on VMS. (file-name-nondirectory "[X]FOO.TMP") => "FOO.TMP" - Function: file-name-sans-versions FILENAME This function returns FILENAME with any file version numbers, backup version numbers, or trailing tildes deleted. (file-name-sans-versions "~rms/foo.~1~") => "~rms/foo" (file-name-sans-versions "~rms/foo~") => "~rms/foo" (file-name-sans-versions "~rms/foo") => "~rms/foo" ;; The following example applies to VMS only. (file-name-sans-versions "foo;23") => "foo" - Function: file-name-sans-extension FILENAME This function returns FILENAME minus its "extension," if any. The extension, in a file name, is the part that starts with the last `.' in the last name component. For example, (file-name-sans-extension "foo.lose.c") => "foo.lose" (file-name-sans-extension "big.hack/foo") => "big.hack/foo"  File: elisp, Node: Directory Names, Next: Relative File Names, Prev: File Name Components, Up: File Names Directory Names --------------- A "directory name" is the name of a directory. A directory is a kind of file, and it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On Unix, this is simple: a directory name ends in a slash, whereas the directory's name as a file lacks that slash. On VMS, the relationship is more complicated. The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable. The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as `$HOME', and the constructs `~', and `..'. - Function: file-name-as-directory FILENAME This function returns a string representing FILENAME in a form that the operating system will interpret as the name of a directory. In Unix, this means appending a slash to the string (if it does not already end in one). On VMS, the function converts a string of the form `[X]Y.DIR.1' to the form `[X.Y]'. (file-name-as-directory "~rms/lewis") => "~rms/lewis/" - Function: directory-file-name DIRNAME This function returns a string representing DIRNAME in a form that the operating system will interpret as the name of a file. On Unix, this means removing the final slash from the string. On VMS, the function converts a string of the form `[X.Y]' to `[X]Y.DIR.1'. (directory-file-name "~lewis/") => "~lewis" Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as "the name" of the directory, and find it annoying to see the directory's "real" name. If you define the link name as an abbreviation for the "real" name, Emacs shows users the abbreviation instead. - Variable: directory-abbrev-alist The variable `directory-abbrev-alist' contains an alist of abbreviations to use for file directories. Each element has the form `(FROM . TO)', and says to replace FROM with TO when it appears in a directory name. The FROM string is actually a regular expression; it should always start with `^'. The function `abbreviate-file-name' performs these substitutions. You can set this variable in `site-init.el' to describe the abbreviations appropriate for your site. Here's an example, from a system on which file system `/home/fsf' and so on are normally accessed through symbolic links named `/fsf' and so on. (("^/home/fsf" . "/fsf") ("^/home/gp" . "/gp") ("^/home/gd" . "/gd")) To convert a directory name to its abbreviation, use this function: - Function: abbreviate-file-name DIRNAME This function applies abbreviations from `directory-abbrev-alist' to its argument, and substitutes `~' for the user's home directory.  File: elisp, Node: Relative File Names, Next: File Name Expansion, Prev: Directory Names, Up: File Names Absolute and Relative File Names -------------------------------- All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an "absolute" file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a "relative" file name. On Unix, an absolute file name starts with a slash or a tilde (`~'), and a relative one does not. The rules on VMS are complicated. - Function: file-name-absolute-p FILENAME This function returns `t' if file FILENAME is an absolute file name, `nil' otherwise. On VMS, this function understands both Unix syntax and VMS syntax. (file-name-absolute-p "~rms/foo") => t (file-name-absolute-p "rms/foo") => nil (file-name-absolute-p "/user/rms/foo") => t  File: elisp, Node: File Name Expansion, Next: Unique File Names, Prev: Relative File Names, Up: File Names Functions that Expand Filenames ------------------------------- "Expansion" of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as `./' and `NAME/../'. - Function: expand-file-name FILENAME &optional DIRECTORY This function converts FILENAME to an absolute file name. If DIRECTORY is supplied, it is the default directory to start with if FILENAME is relative. (The value of DIRECTORY should itself be an absolute directory name; it may start with `~'.) Otherwise, the current buffer's value of `default-directory' is used. For example: (expand-file-name "foo") => "/xcssun/users/rms/lewis/foo" (expand-file-name "../foo") => "/xcssun/users/rms/foo" (expand-file-name "foo" "/usr/spool/") => "/usr/spool/foo" (expand-file-name "$HOME/foo") => "/xcssun/users/rms/lewis/$HOME/foo" Filenames containing `.' or `..' are simplified to their canonical form: (expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo" Note that `expand-file-name' does *not* expand environment variables; only `substitute-in-file-name' does that. - Function: file-relative-name FILENAME DIRECTORY This function does the inverse of expansion--it tries to return a relative name that is equivalent to FILENAME when interpreted relative to DIRECTORY. On some operating systems, an absolute file name begins with a device name. On such systems, FILENAME has no relative equivalent based on DIRECTORY if they start with two different device names. In this case, `file-relative-name' returns FILENAME in absolute form. (file-relative-name "/foo/bar" "/foo/") => "bar" (file-relative-name "/foo/bar" "/hack/") => "/foo/bar" - Variable: default-directory The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with `~'. This variable is buffer-local in every buffer. `expand-file-name' uses the default directory when its second argument is `nil'. On Unix systems, the value is always a string ending with a slash. default-directory => "/user/lewis/manual/" - Function: substitute-in-file-name FILENAME This function replaces environment variables references in FILENAME with the environment variable values. Following standard Unix shell syntax, `$' is the prefix to substitute an environment variable value. The environment variable name is the series of alphanumeric characters (including underscores) that follow the `$'. If the character following the `$' is a `{', then the variable name is everything up to the matching `}'. Here we assume that the environment variable `HOME', which holds the user's home directory name, has value `/xcssun/users/rms'. (substitute-in-file-name "$HOME/foo") => "/xcssun/users/rms/foo" After substitution, if a `~' or a `/' appears following a `/', everything before the following `/' is discarded: (substitute-in-file-name "bar/~/foo") => "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") => "/xcssun/users/rms/foo" ;; `/usr/local/' has been discarded. On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.