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This is Info file ../../info/lispref.info, produced by Makeinfo-1.63 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 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Copyright (C) 1995 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: 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 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 job, 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. File: lispref.info, 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 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: 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: lispref.info, 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: lispref.info, 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 expanding to get rid of `.' and `..' 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 &optional DEFAULT 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. If the filename is relative, DEFAULT is the directory to start with. If DEFAULT is `nil' or missing, the current buffer's value of `default-directory' is used. *Note Buffer File Name::, for related information. File: lispref.info, 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 File Attributes::.). 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. 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. Unfortunately, you cannot convert this number into a time string in XEmacs. `(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: lispref.info, Node: Changing File Attributes, 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. - Command: 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 -l fo* -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Then we evaluate the form `(add-name-to-file "~/lewis/foo" "~/lewis/foo2")'. Again we list the files. This shows two names, `foo' and `foo2'. (add-name-to-file "~/lewis/foo1" "~/lewis/foo2") => nil % ls -l fo* -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Finally, we evaluate the following: (add-name-to-file "~/lewis/foo" "~/lewis/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 "~/lewis/foo1" "~/lewis/foo3") => nil % ls -l fo* -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3 This function is meaningless on VMS, 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 functions gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) 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 XEmacs and its subprocesses. Every file created with XEmacs initially has this protection. On Unix, the default protection is the bitwise complement of the "umask" value. The argument MODE must be an integer. Only the low 9 bits of MODE are used. 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: lispref.info, Node: File Names, Next: Contents of Directories, Prev: Changing File Attributes, Up: Files File Names ========== Files are generally referred to by their names, in XEmacs as elsewhere. File names in XEmacs 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 the 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, these functions understand MS-DOS 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. File: lispref.info, 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, XEmacs 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 XEmacs omits the version number. Version numbers 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 &optional KEEP-BACKUP-VERSION This function returns FILENAME without any file version numbers, backup version numbers, or trailing tildes. If KEEP-BACKUP-VERSION is non-`nil', we do not remove backup version numbers, only true file version numbers. (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: lispref.info, 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 XEmacs 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. 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 a 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, XEmacs shows users the abbreviation instead. If you wish to convert a directory name to its abbreviation, use this function: - Function: abbreviate-file-name DIRNAME &optional HACK-HOMEDIR This function applies abbreviations from `directory-abbrev-alist' to its argument, and substitutes `~' for the user's home directory. If HACK-HOMEDIR is non-`nil', then this also substitutes `~' for the user's home directory. - 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: lispref.info, 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: lispref.info, 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 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/$HOME/foo" Filenames containing `.' or `..' are simplified to their canonical form: (expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo" `~/' is expanded into the user's home directory. A `/' or `~' following a `/' is taken to be the start of an absolute file name that overrides what precedes it, so everything before that `/' or `~' is deleted. For example: (expand-file-name "/a1/gnu//usr/local/lib/emacs/etc/MACHINES") => "/usr/local/lib/emacs/etc/MACHINES" (expand-file-name "/a1/gnu/~/foo") => "/xcssun/users/rms/foo" In both cases, `/a1/gnu/' is discarded because an absolute file name follows it. Note that `expand-file-name' does *not* expand environment variables; only `substitute-in-file-name' does that. - Function: file-relative-name FILENAME &optional DIRECTORY This function does the inverse of expansion--it tries to return a relative name that is equivalent to FILENAME when interpreted relative to DIRECTORY. (If such a relative name would be longer than the absolute name, it returns the absolute name instead.) If DIRECTORY is `nil' or omitted, the value of `default-directory' is used. (file-relative-name "/foo/bar" "/foo/") => "bar") (file-relative-name "/foo/bar" "/hack/") => "/foo/bar") - Variable: default-directory The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with `~'. This variable is local in every buffer. `expand-file-name' uses the default directory when its second argument is `nil'. On Unix systems, the value is always a string ending with a slash. default-directory => "/user/lewis/manual/" - Function: substitute-in-file-name FILENAME This function replaces environment variables references in FILENAME with the environment variable values. Following standard Unix shell syntax, `$' 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 "$HOME/foo") => "/xcssun/users/rms/foo" If a `~' or a `/' appears following a `/', after substitution, everything before the following `/' is discarded: (substitute-in-file-name "bar/~/foo") => "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") => "/xcssun/users/rms/foo" On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above. File: lispref.info, Node: Unique File Names, Next: File Name Completion, Prev: File Name Expansion, Up: File Names Generating Unique File Names ---------------------------- Some programs need to write temporary files. Here is the usual way to construct a name for such a file: (make-temp-name (concat "/tmp/" NAME-OF-APPLICATION)) Here we use the directory `/tmp/' because that is the standard place on Unix for temporary files. The job of `make-temp-name' is to prevent two different users or two different jobs from trying to use the same name. - Function: make-temp-name STRING This function generates string that can be used as a unique name. The name starts with STRING, and ends with a number that is different in each XEmacs job. (make-temp-name "/tmp/foo") => "/tmp/foo021304" To prevent conflicts among different libraries running in the same XEmacs, each Lisp program that uses `make-temp-name' should have its own STRING. The number added to the end of the name distinguishes between the same application running in different XEmacs jobs. File: lispref.info, Node: File Name Completion, Prev: Unique File Names, Up: File Names File Name Completion -------------------- This section describes low-level subroutines for completing a file name. For other completion functions, see *Note Completion::. - Function: file-name-all-completions PARTIAL-FILENAME DIRECTORY This function returns a list of all possible completions for a file whose name starts with PARTIAL-FILENAME in directory DIRECTORY. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information. The argument PARTIAL-FILENAME must be a file name containing no directory part and no slash. The current buffer's default directory is prepended to DIRECTORY, if DIRECTORY is not absolute. In the following example, suppose that the current default directory, `~rms/lewis', has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'. (file-name-all-completions "f" "") => ("foo" "file~" "file.c.~2~" "file.c.~1~" "file.c") (file-name-all-completions "fo" "") => ("foo") - Function: file-name-completion FILENAME DIRECTORY This function completes the file name FILENAME in directory DIRECTORY. It returns the longest prefix common to all file names in directory DIRECTORY that start with FILENAME. If only one match exists and FILENAME matches it exactly, the function returns `t'. The function returns `nil' if directory DIRECTORY contains no name starting with FILENAME. In the following example, suppose that the current default directory has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'. (file-name-completion "fi" "") => "file" (file-name-completion "file.c.~1" "") => "file.c.~1~" (file-name-completion "file.c.~1~" "") => t (file-name-completion "file.c.~3" "") => nil - User Option: completion-ignored-extensions `file-name-completion' usually ignores file names that end in any string in this list. It does not ignore them when all the possible completions end in one of these suffixes or when a buffer showing all possible completions is displayed. A typical value might look like this: completion-ignored-extensions => (".o" ".elc" "~" ".dvi") File: lispref.info, Node: Contents of Directories, Next: Create/Delete Dirs, Prev: File Names, Up: Files Contents of Directories ======================= A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system. XEmacs can list the names of the files in a directory as a Lisp list, or display the names in a buffer using the `ls' shell command. In the latter case, it can optionally display information about each file, depending on the value of switches passed to the `ls' command. - Function: directory-files DIRECTORY &optional FULL-NAME MATCH-REGEXP NOSORT FILES-ONLY This function returns a list of the names of the files in the directory DIRECTORY. By default, the list is in alphabetical order. If FULL-NAME is non-`nil', the function returns the files' absolute file names. Otherwise, it returns just the names relative to the specified directory. If MATCH-REGEXP is non-`nil', this function returns only those file names that contain that regular expression--the other file names are discarded from the list. If NOSORT is non-`nil', `directory-files' does not sort the list, so you get the file names in no particular order. Use this if you want the utmost possible speed and don't care what order the files are processed in. If the order of processing is visible to the user, then the user will probably be happier if you do sort the names. If FILES-ONLY is the symbol `t', then only the "files" in the directory will be returned; subdirectories will be excluded. If FILES-ONLY is not `nil' and not `t', then only the subdirectories will be returned. Otherwise, if FILES-ONLY is `nil' (the default) then both files and subdirectories will be returned. (directory-files "~lewis") => ("#foo#" "#foo.el#" "." ".." "dired-mods.el" "files.texi" "files.texi.~1~") An error is signaled if DIRECTORY is not the name of a directory that can be read. - Function: insert-directory FILE SWITCHES &optional WILDCARD FULL-DIRECTORY-P This function inserts (in the current buffer) a directory listing for directory FILE, formatted with `ls' according to SWITCHES. It leaves point after the inserted text. The argument FILE may be either a directory name or a file specification including wildcard characters. If WILDCARD is non-`nil', that means treat FILE as a file specification with wildcards. If FULL-DIRECTORY-P is non-`nil', that means FILE is a directory and switches do not contain `-d', so that the listing should show the full contents of the directory. (The `-d' option to `ls' says to describe a directory itself rather than its contents.) This function works by running a directory listing program whose name is in the variable `insert-directory-program'. If WILDCARD is non-`nil', it also runs the shell specified by `shell-file-name', to expand the wildcards. - Variable: insert-directory-program This variable's value is the program to run to generate a directory listing for the function `insert-directory'. File: lispref.info, Node: Create/Delete Dirs, Next: Magic File Names, Prev: Contents of Directories, Up: Files Creating and Deleting Directories ================================= Most Emacs Lisp file-manipulation functions get errors when used on files that are directories. For example, you cannot delete a directory with `delete-file'. These special functions exist to create and delete directories. - Command: make-directory DIRNAME &optional PARENTS This function creates a directory named DIRNAME. Interactively, the default choice of directory to create is the current default directory for file names. That is useful when you have visited a file in a nonexistent directory. Non-interactively, optional argument PARENTS says whether to create parent directories if they don't exist. (Interactively, this always happens.) - Command: delete-directory DIRNAME This function deletes the directory named DIRNAME. The function `delete-file' does not work for files that are directories; you must use `delete-directory' in that case.