This is elisp, produced by makeinfo version 4.0f from ./elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 21.2. 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, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Copying", with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."  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 at all levels until none remain, then simplifying away `.' and `..' appearing as name components. This results in a sort of canonical name for the file. A file does not always 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 truename of the file FILENAME. The argument must be an absolute file name. - Function: file-chase-links filename This function follows symbolic links, starting with FILENAME, until it finds a file name which is not the name of a symbolic link. Then it returns that file name. To illustrate the difference between `file-chase-links' and `file-truename', suppose that `/usr/foo' is a symbolic link to the directory `/home/foo', and `/home/foo/hello' is an ordinary file (or at least, not a symbolic link) or nonexistent. Then we would have: (file-chase-links "/usr/foo/hello") ;; This does not follow the links in the parent directories. => "/usr/foo/hello" (file-truename "/usr/foo/hello") ;; Assuming that `/home' is not a symbolic link. => "/home/foo/hello" *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. If the size is too large to fit in a Lisp integer, this is a floating point number. 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. Depending on the magnitude of the value, this can be either an integer or a cons cell, in the same manner as the inode number. 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 bytes long. (It may not contain 14906 characters, though, if some of the bytes belong to multibyte sequences.) `"-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. Some systems implement multiple names by copying the file instead. 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 and GNU/Linux, 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. This function is not available on systems that don't support symbolic links. - 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, or a subset of it (`write-region' will not give a file execute permission even if the default file protection allows execute permission). On Unix and GNU/Linux, 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. You can use the Lisp construct for octal character codes to enter MODE; for example, (set-default-file-modes ?\644) Saving a modified version of an existing file does not count as creating the file; it preserves the existing file's mode, whatever that is. So the default file protection has no effect. - 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 one of the standard executable extensions, such as `.com', `.bat', `.exe', and some others. Files that begin with the Unix-standard `#!' signature, such as shell and Perl scripts, are also considered as executable files. This is reflected in the values returned by `file-modes' and `file-attributes'. Directories are also reported with executable bit set, for compatibility with Unix.  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 MS-DOS and MS-Windows, these functions (like the function that actually operate on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate the components, as well as Unix syntax; but they always return Unix syntax. On VMS, these functions (and the ones that operate on files) understand both VMS file-name syntax and Unix syntax. This enables Lisp programs to specify file names in Unix syntax and work properly on all systems without change. * 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 most systems, the directory part is everything up to and including the last slash (backslash is also allowed in input on MS-DOS or MS-Windows); 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 most systems, 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 most systems, 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 with any file version numbers, backup version numbers, or trailing tildes discarded. If KEEP-BACKUP-VERSION is non-`nil', then true file version numbers understood as such by the file system are discarded from the return value, but backup version numbers are kept. (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" - Function: file-name-extension filename &optional period This function returns FILENAME's final "extension," if any, after applying `file-name-sans-versions' to remove any version/backup part. If PERIOD is non-nil, then the returned value includes the period that delimits the extension, and if FILENAME has no extension, the value is `""'.  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 most systems, this is simple: a directory name ends in a slash (or backslash), 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. On most systems, 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 most systems, this means removing the final slash (or backslash) 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 and GNU/Linux, an absolute file name starts with a slash or a tilde (`~'), and a relative one does not. On MS-DOS and MS-Windows, an absolute file name starts with a slash or a backslash, or with a drive specification `X:/', where X is the "drive letter". 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/$HOME/foo" Filenames containing `.' or `..' are simplified to their canonical form: (expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo" Note that `expand-file-name' does _not_ expand environment variables; only `substitute-in-file-name' does that. - Function: file-relative-name filename &optional directory This function does the inverse of expansion--it tries to return a relative name that is equivalent to FILENAME when interpreted relative to DIRECTORY. If DIRECTORY is omitted or `nil', it defaults to the current buffer's default directory. On some operating systems, an absolute file name begins with a device name. On such systems, FILENAME has no relative equivalent based on DIRECTORY if they start with two different device names. In this case, `file-relative-name' returns FILENAME in absolute form. (file-relative-name "/foo/bar" "/foo/") => "bar" (file-relative-name "/foo/bar" "/hack/") => "../foo/bar" - Variable: default-directory The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with `~'. This variable is buffer-local in every buffer. `expand-file-name' uses the default directory when its second argument is `nil'. Aside from VMS, the value is always a string ending with a slash. default-directory => "/user/lewis/manual/" - Function: substitute-in-file-name filename This function replaces environment variables references in FILENAME with the environment variable values. Following standard Unix shell syntax, `$' 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.  File: elisp, 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, starting in Emacs 21: (make-temp-file NAME-OF-APPLICATION) The job of `make-temp-file' is to prevent two different users or two different jobs from trying to use the exact same file name. - Function: make-temp-file prefix &optional dir-flag This function creates a temporary file and returns its name. The name starts with PREFIX; it also contains a number that is different in each Emacs job. If PREFIX is a relative file name, it is expanded against `temporary-file-directory'. (make-temp-file "foo") => "/tmp/foo232J6v" When `make-temp-file' returns, the file has been created and is empty. At that point, you should write the intended contents into the file. If DIR-FLAG is non-`nil', `make-temp-file' creates an empty directory instead of an empty file. To prevent conflicts among different libraries running in the same Emacs, each Lisp program that uses `make-temp-file' should have its own PREFIX. The number added to the end of PREFIX distinguishes between the same application running in different Emacs jobs. Additional added characters permit a large number of distinct names even in one Emacs job. The default directory for temporary files is controlled by the variable `temporary-file-directory'. This variable gives the user a uniform way to specify the directory for all temporary files. Some programs use `small-temporary-file-directory' instead, if that is non-`nil'. To use it, you should expand the prefix against the proper directory before calling `make-temp-file'. In older Emacs versions where `make-temp-file' does not exist, you should use `make-temp-name' instead: (make-temp-name (expand-file-name NAME-OF-APPLICATION temporary-file-directory)) - Function: make-temp-name string This function generates a string that can be used as a unique file name. The name starts with STRING, and contains a number that is different in each Emacs job. It is like `make-temp-file' except that it just constructs a name, and does not create a file. On MS-DOS, the STRING prefix can be truncated to fit into the 8+3 file-name limits. - Variable: temporary-file-directory This variable specifies the directory name for creating temporary files. Its value should be a directory name (*note Directory Names::), but it is good for Lisp programs to cope if the value is a directory's file name instead. Using the value as the second argument to `expand-file-name' is a good way to achieve that. The default value is determined in a reasonable way for your operating system; it is based on the `TMPDIR', `TMP' and `TEMP' environment variables, with a fall-back to a system-dependent name if none of these variables is defined. Even if you do not use `make-temp-name' to choose the temporary file's name, you should still use this variable to decide which directory to put the file in. However, if you expect the file to be small, you should use `small-temporary-file-directory' first if that is non-`nil'. - Variable: small-temporary-file-directory This variable (new in Emacs 21) specifies the directory name for creating certain temporary files, which are likely to be small. If you want to write a temporary file which is likely to be small, you should compute the directory like this: (make-temp-file (expand-file-name PREFIX (or small-temporary-file-directory temporary-file-directory)))  File: elisp, Node: File Name Completion, Next: Standard File Names, 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 (or backslash on some systems). The current buffer's default directory is prepended to DIRECTORY, if DIRECTORY is not absolute. In the following example, suppose that `~rms/lewis' is the current default directory, and 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: elisp, Node: Standard File Names, Prev: File Name Completion, Up: File Names Standard File Names ------------------- Most of the file names used in Lisp programs are entered by the user. But occasionally a Lisp program needs to specify a standard file name for a particular use--typically, to hold customization information about each user. For example, abbrev definitions are stored (by default) in the file `~/.abbrev_defs'; the `completion' package stores completions in the file `~/.completions'. These are two of the many standard file names used by parts of Emacs for certain purposes. Various operating systems have their own conventions for valid file names and for which file names to use for user profile data. A Lisp program which reads a file using a standard file name ought to use, on each type of system, a file name suitable for that system. The function `convert-standard-filename' makes this easy to do. - Function: convert-standard-filename filename This function alters the file name FILENAME to fit the conventions of the operating system in use, and returns the result as a new string. The recommended way to specify a standard file name in a Lisp program is to choose a name which fits the conventions of GNU and Unix systems, usually with a nondirectory part that starts with a period, and pass it to `convert-standard-filename' instead of using it directly. Here is an example from the `completion' package: (defvar save-completions-file-name (convert-standard-filename "~/.completions") "*The file name to save completions to.") On GNU and Unix systems, and on some other systems as well, `convert-standard-filename' returns its argument unchanged. On some other systems, it alters the name to fit the system's conventions. For example, on MS-DOS the alterations made by this function include converting a leading `.' to `_', converting a `_' in the middle of the name to `.' if there is no other `.', inserting a `.' after eight characters if there is none, and truncating to three characters after the `.'. (It makes other changes as well.) Thus, `.abbrev_defs' becomes `_abbrev.def', and `.completions' becomes `_complet.ion'.  File: elisp, 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. Emacs 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 options passed to the `ls' command. - Function: directory-files directory &optional full-name match-regexp nosort 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 the names relative to the specified directory. If MATCH-REGEXP is non-`nil', this function returns only those file names that contain a match for that regular expression--the other file names are excluded 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. (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: file-name-all-versions file dirname This function returns a list of all versions of the file named FILE in directory DIRNAME. - Function: file-expand-wildcards pattern &optional full This function expands the wildcard pattern PATTERN, returning a list of file names that match it. If PATTERN is written as an absolute file name, the values are absolute also. If PATTERN is written as a relative file name, it is interpreted relative to the current default directory. The file names returned are normally also relative to the current default directory. However, if FULL is non-`nil', they are absolute. - 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 the directory listing is expected to show the full contents of a directory. You should specify `t' when FILE is a directory and switches do not contain `-d'. (The `-d' option to `ls' says to describe a directory itself as a file, rather than showing its contents.) On most systems, 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. MS-DOS and MS-Windows systems usually lack the standard Unix program `ls', so this function emulates the standard Unix program `ls' with Lisp code. - Variable: insert-directory-program This variable's value is the program to run to generate a directory listing for the function `insert-directory'. It is ignored on systems which generate the listing with Lisp code.  File: elisp, 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. - Function: make-directory dirname &optional parents This function creates a directory named DIRNAME. If PARENTS is non-`nil', that means to create the parent directories first, if they don't already exist. - Function: 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' for them. If the directory contains any files, `delete-directory' signals an error.  File: elisp, Node: Magic File Names, Next: Format Conversion, Prev: Create/Delete Dirs, Up: Files Making Certain File Names "Magic" ================================= You can implement special handling for certain file names. This is called making those names "magic". The principal use for this feature is in implementing remote file names (*note Remote Files: (emacs)Remote Files.). To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match. The variable `file-name-handler-alist' holds a list of handlers, together with regular expressions that determine when to apply each handler. Each element has this form: (REGEXP . HANDLER) All the Emacs primitives for file access and file name transformation check the given file name against `file-name-handler-alist'. If the file name matches REGEXP, the primitives handle that file by calling HANDLER. The first argument given to HANDLER is the name of the primitive; the remaining arguments are the arguments that were passed to that primitive. (The first of these arguments is most often the file name itself.) For example, if you do this: (file-exists-p FILENAME) and FILENAME has handler HANDLER, then HANDLER is called like this: (funcall HANDLER 'file-exists-p FILENAME) When a function takes two or more arguments that must be file names, it checks each of those names for a handler. For example, if you do this: (expand-file-name FILENAME DIRNAME) then it checks for a handler for FILENAME and then for a handler for DIRNAME. In either case, the HANDLER is called like this: (funcall HANDLER 'expand-file-name FILENAME DIRNAME) The HANDLER then needs to figure out whether to handle FILENAME or DIRNAME. Here are the operations that a magic file name handler gets to handle: `add-name-to-file', `copy-file', `delete-directory', `delete-file', `diff-latest-backup-file', `directory-file-name', `directory-files', `dired-call-process', `dired-compress-file', `dired-uncache', `expand-file-name', `file-accessible-directory-p', `file-attributes', `file-directory-p', `file-executable-p', `file-exists-p', `file-local-copy', `file-modes', `file-name-all-completions', `file-name-as-directory', `file-name-completion', `file-name-directory', `file-name-nondirectory', `file-name-sans-versions', `file-newer-than-file-p', `file-ownership-preserved-p', `file-readable-p', `file-regular-p', `file-symlink-p', `file-truename', `file-writable-p', `find-backup-file-name', `get-file-buffer', `insert-directory', `insert-file-contents', `load', `make-directory', `make-symbolic-link', `rename-file', `set-file-modes', `set-visited-file-modtime', `shell-command', `unhandled-file-name-directory', `vc-registered', `verify-visited-file-modtime', `write-region'. Handlers for `insert-file-contents' typically need to clear the buffer's modified flag, with `(set-buffer-modified-p nil)', if the VISIT argument is non-`nil'. This also has the effect of unlocking the buffer if it is locked. The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself--when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation "in the usual way". It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this: (defun my-file-handler (operation &rest args) ;; First check for the specific operations ;; that we have special handling for. (cond ((eq operation 'insert-file-contents) ...) ((eq operation 'write-region) ...) ... ;; Handle any operation we don't know about. (t (let ((inhibit-file-name-handlers (cons 'my-file-handler (and (eq inhibit-file-name-operation operation) inhibit-file-name-handlers))) (inhibit-file-name-operation operation)) (apply operation args))))) When a handler function decides to call the ordinary Emacs primitive for the operation at hand, it needs to prevent the primitive from calling the same handler once again, thus leading to an infinite recursion. The example above shows how to do this, with the variables `inhibit-file-name-handlers' and `inhibit-file-name-operation'. Be careful to use them exactly as shown above; the details are crucial for proper behavior in the case of multiple handlers, and for operations that have two file names that may each have handlers. - Variable: inhibit-file-name-handlers This variable holds a list of handlers whose use is presently inhibited for a certain operation. - Variable: inhibit-file-name-operation The operation for which certain handlers are presently inhibited. - Function: find-file-name-handler file operation This function returns the handler function for file name FILE, or `nil' if there is none. The argument OPERATION should be the operation to be performed on the file--the value you will pass to the handler as its first argument when you call it. The operation is needed for comparison with `inhibit-file-name-operation'. - Function: file-local-copy filename This function copies file FILENAME to an ordinary non-magic file, if it isn't one already. If FILENAME specifies a magic file name, which programs outside Emacs cannot directly read or write, this copies the contents to an ordinary file and returns that file's name. If FILENAME is an ordinary file name, not magic, then this function does nothing and returns `nil'. - Function: unhandled-file-name-directory filename This function returns the name of a directory that is not magic. It uses the directory part of FILENAME if that is not magic. For a magic file name, it invokes the file name handler, which therefore decides what value to return. This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.