1@c -*-texinfo-*- 2@c This is part of the GNU Emacs Lisp Reference Manual. 3@c Copyright (C) 1990--1995, 1998--1999, 2001--2021 Free Software 4@c Foundation, Inc. 5@c See the file elisp.texi for copying conditions. 6@node Files 7@chapter Files 8 9 This chapter describes the Emacs Lisp functions and variables to 10find, create, view, save, and otherwise work with files and 11directories. A few other file-related functions are described in 12@ref{Buffers}, and those related to backups and auto-saving are 13described in @ref{Backups and Auto-Saving}. 14 15 Many of the file functions take one or more arguments that are file 16names. A file name is a string. Most of these functions expand file 17name arguments using the function @code{expand-file-name}, so that 18@file{~} is handled correctly, as are relative file names (including 19@file{../} and the empty string). @xref{File Name Expansion}. 20 21 In addition, certain @dfn{magic} file names are handled specially. 22For example, when a remote file name is specified, Emacs accesses the 23file over the network via an appropriate protocol. @xref{Remote 24Files,, Remote Files, emacs, The GNU Emacs Manual}. This handling is 25done at a very low level, so you may assume that all the functions 26described in this chapter accept magic file names as file name 27arguments, except where noted. @xref{Magic File Names}, for details. 28 29 When file I/O functions signal Lisp errors, they usually use the 30condition @code{file-error} (@pxref{Handling Errors}). The error 31message is in most cases obtained from the operating system, according 32to locale @code{system-messages-locale}, and decoded using coding system 33@code{locale-coding-system} (@pxref{Locales}). 34 35@menu 36* Visiting Files:: Reading files into Emacs buffers for editing. 37* Saving Buffers:: Writing changed buffers back into files. 38* Reading from Files:: Reading files into buffers without visiting. 39* Writing to Files:: Writing new files from parts of buffers. 40* File Locks:: Locking and unlocking files, to prevent 41 simultaneous editing by two people. 42* Information about Files:: Testing existence, accessibility, size of files. 43* Changing Files:: Renaming files, changing permissions, etc. 44* Files and Storage:: Surviving power and media failures 45* File Names:: Decomposing and expanding file names. 46* Contents of Directories:: Getting a list of the files in a directory. 47* Create/Delete Dirs:: Creating and Deleting Directories. 48* Magic File Names:: Special handling for certain file names. 49* Format Conversion:: Conversion to and from various file formats. 50@end menu 51 52@node Visiting Files 53@section Visiting Files 54@cindex finding files 55@cindex visiting files 56 57 Visiting a file means reading a file into a buffer. Once this is 58done, we say that the buffer is @dfn{visiting} that file, and call the 59file @dfn{the visited file} of the buffer. 60 61 A file and a buffer are two different things. A file is information 62recorded permanently in the computer (unless you delete it). A 63buffer, on the other hand, is information inside of Emacs that will 64vanish at the end of the editing session (or when you kill the 65buffer). When a buffer is visiting a file, it contains information 66copied from the file. The copy in the buffer is what you modify with 67editing commands. Changes to the buffer do not change the file; to 68make the changes permanent, you must @dfn{save} the buffer, which 69means copying the altered buffer contents back into the file. 70 71 Despite the distinction between files and buffers, people often 72refer to a file when they mean a buffer and vice-versa. Indeed, we 73say, ``I am editing a file'', rather than, ``I am editing a buffer 74that I will soon save as a file of the same name''. Humans do not 75usually need to make the distinction explicit. When dealing with a 76computer program, however, it is good to keep the distinction in mind. 77 78@menu 79* Visiting Functions:: The usual interface functions for visiting. 80* Subroutines of Visiting:: Lower-level subroutines that they use. 81@end menu 82 83@node Visiting Functions 84@subsection Functions for Visiting Files 85@cindex visiting files, functions for 86@cindex how to visit files 87 88 This section describes the functions normally used to visit files. 89For historical reasons, these functions have names starting with 90@samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for 91functions and variables that access the visited file name of a buffer or 92that find an existing buffer by its visited file name. 93 94 In a Lisp program, if you want to look at the contents of a file but 95not alter it, the fastest way is to use @code{insert-file-contents} in a 96temporary buffer. Visiting the file is not necessary and takes longer. 97@xref{Reading from Files}. 98 99@deffn Command find-file filename &optional wildcards 100This command selects a buffer visiting the file @var{filename}, 101using an existing buffer if there is one, and otherwise creating a 102new buffer and reading the file into it. It also returns that buffer. 103 104Aside from some technical details, the body of the @code{find-file} 105function is basically equivalent to: 106 107@smallexample 108(switch-to-buffer (find-file-noselect filename nil nil wildcards)) 109@end smallexample 110 111@noindent 112(See @code{switch-to-buffer} in @ref{Switching Buffers}.) 113 114If @var{wildcards} is non-@code{nil}, which is always true in an 115interactive call, then @code{find-file} expands wildcard characters in 116@var{filename} and visits all the matching files. 117 118When @code{find-file} is called interactively, it prompts for 119@var{filename} in the minibuffer. 120@end deffn 121 122@deffn Command find-file-literally filename 123This command visits @var{filename}, like @code{find-file} does, but it 124does not perform any format conversions (@pxref{Format Conversion}), 125character code conversions (@pxref{Coding Systems}), or end-of-line 126conversions (@pxref{Coding System Basics, End of line conversion}). 127The buffer visiting the file is made unibyte, and its major mode is 128Fundamental mode, regardless of the file name. File local variable 129specifications in the file (@pxref{File Local Variables}) are 130ignored, and automatic decompression and adding a newline at the end 131of the file due to @code{require-final-newline} (@pxref{Saving 132Buffers, require-final-newline}) are also disabled. 133 134Note that if Emacs already has a buffer visiting the same file 135non-literally, it will not visit the same file literally, but instead 136just switch to the existing buffer. If you want to be sure of 137accessing a file's contents literally, you should create a temporary 138buffer and then read the file contents into it using 139@code{insert-file-contents-literally} (@pxref{Reading from Files}). 140@end deffn 141 142@defun find-file-noselect filename &optional nowarn rawfile wildcards 143This function is the guts of all the file-visiting functions. It 144returns a buffer visiting the file @var{filename}. You may make the 145buffer current or display it in a window if you wish, but this 146function does not do so. 147 148The function returns an existing buffer if there is one; otherwise it 149creates a new buffer and reads the file into it. When 150@code{find-file-noselect} uses an existing buffer, it first verifies 151that the file has not changed since it was last visited or saved in 152that buffer. If the file has changed, this function asks the user 153whether to reread the changed file. If the user says @samp{yes}, any 154edits previously made in the buffer are lost. 155 156Reading the file involves decoding the file's contents (@pxref{Coding 157Systems}), including end-of-line conversion, and format conversion 158(@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil}, 159then @code{find-file-noselect} expands wildcard characters in 160@var{filename} and visits all the matching files. 161 162This function displays warning or advisory messages in various peculiar 163cases, unless the optional argument @var{nowarn} is non-@code{nil}. For 164example, if it needs to create a buffer, and there is no file named 165@var{filename}, it displays the message @samp{(New file)} in the echo 166area, and leaves the buffer empty. 167 168The @code{find-file-noselect} function normally calls 169@code{after-find-file} after reading the file (@pxref{Subroutines of 170Visiting}). That function sets the buffer major mode, parses local 171variables, warns the user if there exists an auto-save file more recent 172than the file just visited, and finishes by running the functions in 173@code{find-file-hook}. 174 175If the optional argument @var{rawfile} is non-@code{nil}, then 176@code{after-find-file} is not called, and the 177@code{find-file-not-found-functions} are not run in case of failure. 178What's more, a non-@code{nil} @var{rawfile} value suppresses coding 179system conversion and format conversion. 180 181The @code{find-file-noselect} function usually returns the buffer that 182is visiting the file @var{filename}. But, if wildcards are actually 183used and expanded, it returns a list of buffers that are visiting the 184various files. 185 186@example 187@group 188(find-file-noselect "/etc/fstab") 189 @result{} #<buffer fstab> 190@end group 191@end example 192@end defun 193 194@deffn Command find-file-other-window filename &optional wildcards 195This command selects a buffer visiting the file @var{filename}, but 196does so in a window other than the selected window. It may use 197another existing window or split a window; see @ref{Switching 198Buffers}. 199 200When this command is called interactively, it prompts for 201@var{filename}. 202@end deffn 203 204@deffn Command find-file-read-only filename &optional wildcards 205This command selects a buffer visiting the file @var{filename}, like 206@code{find-file}, but it marks the buffer as read-only. @xref{Read Only 207Buffers}, for related functions and variables. 208 209When this command is called interactively, it prompts for 210@var{filename}. 211@end deffn 212 213@defopt find-file-wildcards 214If this variable is non-@code{nil}, then the various @code{find-file} 215commands check for wildcard characters and visit all the files that 216match them (when invoked interactively or when their @var{wildcards} 217argument is non-@code{nil}). If this option is @code{nil}, then 218the @code{find-file} commands ignore their @var{wildcards} argument 219and never treat wildcard characters specially. 220@end defopt 221 222@defopt find-file-hook 223The value of this variable is a list of functions to be called after a 224file is visited. The file's local-variables specification (if any) will 225have been processed before the hooks are run. The buffer visiting the 226file is current when the hook functions are run. 227 228This variable is a normal hook. @xref{Hooks}. 229@end defopt 230 231@defvar find-file-not-found-functions 232The value of this variable is a list of functions to be called when 233@code{find-file} or @code{find-file-noselect} is passed a nonexistent 234file name. @code{find-file-noselect} calls these functions as soon as 235it detects a nonexistent file. It calls them in the order of the list, 236until one of them returns non-@code{nil}. @code{buffer-file-name} is 237already set up. 238 239This is not a normal hook because the values of the functions are 240used, and in many cases only some of the functions are called. 241@end defvar 242 243@defvar find-file-literally 244This buffer-local variable, if set to a non-@code{nil} value, makes 245@code{save-buffer} behave as if the buffer were visiting its file 246literally, i.e., without conversions of any kind. The command 247@code{find-file-literally} sets this variable's local value, but other 248equivalent functions and commands can do that as well, e.g., to avoid 249automatic addition of a newline at the end of the file. This variable 250is permanent local, so it is unaffected by changes of major modes. 251@end defvar 252 253@node Subroutines of Visiting 254@subsection Subroutines of Visiting 255 256 The @code{find-file-noselect} function uses two important subroutines 257which are sometimes useful in user Lisp code: @code{create-file-buffer} 258and @code{after-find-file}. This section explains how to use them. 259 260@c FIXME This does not describe the default behavior, because 261@c uniquify is enabled by default and advises this function. 262@c This is confusing. uniquify should be folded into the function proper. 263@defun create-file-buffer filename 264This function creates a suitably named buffer for visiting 265@var{filename}, and returns it. It uses @var{filename} (sans directory) 266as the name if that name is free; otherwise, it appends a string such as 267@samp{<2>} to get an unused name. See also @ref{Creating Buffers}. 268Note that the @file{uniquify} library affects the result of this 269function. @xref{Uniquify,,, emacs, The GNU Emacs Manual}. 270 271@strong{Please note:} @code{create-file-buffer} does @emph{not} 272associate the new buffer with a file and does not select the buffer. 273It also does not use the default major mode. 274 275@example 276@group 277(create-file-buffer "foo") 278 @result{} #<buffer foo> 279@end group 280@group 281(create-file-buffer "foo") 282 @result{} #<buffer foo<2>> 283@end group 284@group 285(create-file-buffer "foo") 286 @result{} #<buffer foo<3>> 287@end group 288@end example 289 290This function is used by @code{find-file-noselect}. 291It uses @code{generate-new-buffer} (@pxref{Creating Buffers}). 292@end defun 293 294@defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes 295This function sets the buffer major mode, and parses local variables 296(@pxref{Auto Major Mode}). It is called by @code{find-file-noselect} 297and by the default revert function (@pxref{Reverting}). 298 299@cindex new file message 300@cindex file open error 301If reading the file got an error because the file does not exist, but 302its directory does exist, the caller should pass a non-@code{nil} value 303for @var{error}. In that case, @code{after-find-file} issues a warning: 304@samp{(New file)}. For more serious errors, the caller should usually not 305call @code{after-find-file}. 306 307If @var{warn} is non-@code{nil}, then this function issues a warning 308if an auto-save file exists and is more recent than the visited file. 309 310If @var{noauto} is non-@code{nil}, that says not to enable or disable 311Auto-Save mode. The mode remains enabled if it was enabled before. 312 313If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that 314means this call was from @code{revert-buffer}. This has no direct 315effect, but some mode functions and hook functions check the value 316of this variable. 317 318If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's 319major mode, don't process local variables specifications in the file, 320and don't run @code{find-file-hook}. This feature is used by 321@code{revert-buffer} in some cases. 322 323The last thing @code{after-find-file} does is call all the functions 324in the list @code{find-file-hook}. 325@end defun 326 327@node Saving Buffers 328@section Saving Buffers 329@cindex saving buffers 330 331 When you edit a file in Emacs, you are actually working on a buffer 332that is visiting that file---that is, the contents of the file are 333copied into the buffer and the copy is what you edit. Changes to the 334buffer do not change the file until you @dfn{save} the buffer, which 335means copying the contents of the buffer into the file. Buffers which 336are not visiting a file can still be ``saved'', in a sense, using 337functions in the buffer-local @code{write-contents-functions} hook. 338 339@deffn Command save-buffer &optional backup-option 340This function saves the contents of the current buffer in its visited 341file if the buffer has been modified since it was last visited or saved. 342Otherwise it does nothing. 343 344@code{save-buffer} is responsible for making backup files. Normally, 345@var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup 346file only if this is the first save since visiting the file. Other 347values for @var{backup-option} request the making of backup files in 348other circumstances: 349 350@itemize @bullet 351@item 352With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the 353@code{save-buffer} function marks this version of the file to be 354backed up when the buffer is next saved. 355 356@item 357With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the 358@code{save-buffer} function unconditionally backs up the previous 359version of the file before saving it. 360 361@item 362With an argument of 0, unconditionally do @emph{not} make any backup file. 363@end itemize 364@end deffn 365 366@deffn Command save-some-buffers &optional save-silently-p pred 367@anchor{Definition of save-some-buffers} 368This command saves some modified file-visiting buffers. Normally it 369asks the user about each buffer. But if @var{save-silently-p} is 370non-@code{nil}, it saves all the file-visiting buffers without 371querying the user. 372 373@vindex save-some-buffers-default-predicate 374The optional @var{pred} argument provides a predicate that controls 375which buffers to ask about (or to save silently if 376@var{save-silently-p} is non-@code{nil}). If @var{pred} is 377@code{nil}, that means to use the value of 378@code{save-some-buffers-default-predicate} instead of @var{pred}. If 379the result is @code{nil}, it means ask only about file-visiting 380buffers. If it is @code{t}, that means also offer to save certain 381other non-file buffers---those that have a non-@code{nil} buffer-local 382value of @code{buffer-offer-save} (@pxref{Killing Buffers}). A user 383who says @samp{yes} to saving a non-file buffer is asked to specify 384the file name to use. The @code{save-buffers-kill-emacs} function 385passes the value @code{t} for @var{pred}. 386 387If the predicate is neither @code{t} nor @code{nil}, then it should be 388a function of no arguments. It will be called in each buffer to decide 389whether to offer to save that buffer. If it returns a non-@code{nil} 390value in a certain buffer, that means do offer to save that buffer. 391@end deffn 392 393@deffn Command write-file filename &optional confirm 394@anchor{Definition of write-file} 395This function writes the current buffer into file @var{filename}, makes 396the buffer visit that file, and marks it not modified. Then it renames 397the buffer based on @var{filename}, appending a string like @samp{<2>} 398if necessary to make a unique buffer name. It does most of this work by 399calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and 400@code{save-buffer}. 401 402If @var{confirm} is non-@code{nil}, that means to ask for confirmation 403before overwriting an existing file. Interactively, confirmation is 404required, unless the user supplies a prefix argument. 405 406If @var{filename} is a directory name (@pxref{Directory Names}), 407@code{write-file} uses the name of the visited file, in directory 408@var{filename}. If the buffer is not visiting a file, it uses the 409buffer name instead. 410@end deffn 411 412 Saving a buffer runs several hooks. It also performs format 413conversion (@pxref{Format Conversion}). Note that these hooks, 414described below, are only run by @code{save-buffer}, they are not run 415by other primitives and functions that write buffer text to files, and 416in particular auto-saving (@pxref{Auto-Saving}) doesn't run these 417hooks. 418 419@defvar write-file-functions 420The value of this variable is a list of functions to be called before 421writing out a buffer to its visited file. If one of them returns 422non-@code{nil}, the file is considered already written and the rest of 423the functions are not called, nor is the usual code for writing the file 424executed. 425 426If a function in @code{write-file-functions} returns non-@code{nil}, it 427is responsible for making a backup file (if that is appropriate). 428To do so, execute the following code: 429 430@example 431(or buffer-backed-up (backup-buffer)) 432@end example 433 434You might wish to save the file modes value returned by 435@code{backup-buffer} and use that (if non-@code{nil}) to set the mode 436bits of the file that you write. This is what @code{save-buffer} 437normally does. @xref{Making Backups,, Making Backup Files}. 438 439The hook functions in @code{write-file-functions} are also responsible 440for encoding the data (if desired): they must choose a suitable coding 441system and end-of-line conversion (@pxref{Lisp and Coding Systems}), 442perform the encoding (@pxref{Explicit Encoding}), and set 443@code{last-coding-system-used} to the coding system that was used 444(@pxref{Encoding and I/O}). 445 446If you set this hook locally in a buffer, it is assumed to be 447associated with the file or the way the contents of the buffer were 448obtained. Thus the variable is marked as a permanent local, so that 449changing the major mode does not alter a buffer-local value. On the 450other hand, calling @code{set-visited-file-name} will reset it. 451If this is not what you want, you might like to use 452@code{write-contents-functions} instead. 453 454Even though this is not a normal hook, you can use @code{add-hook} and 455@code{remove-hook} to manipulate the list. @xref{Hooks}. 456@end defvar 457 458@c Emacs 19 feature 459@defvar write-contents-functions 460This works just like @code{write-file-functions}, but it is intended 461for hooks that pertain to the buffer's contents, not to the particular 462visited file or its location, and can be used to create arbitrary save 463processes for buffers that aren't visiting files at all. Such hooks 464are usually set up by major modes, as buffer-local bindings for this 465variable. This variable automatically becomes buffer-local whenever 466it is set; switching to a new major mode always resets this variable, 467but calling @code{set-visited-file-name} does not. 468 469If any of the functions in this hook returns non-@code{nil}, the file 470is considered already written and the rest are not called and neither 471are the functions in @code{write-file-functions}. 472 473When using this hook to save buffers that are not visiting files (for 474instance, special-mode buffers), keep in mind that, if the function 475fails to save correctly and returns a @code{nil} value, 476@code{save-buffer} will go on to prompt the user for a file to save 477the buffer in. If this is undesirable, consider having the function 478fail by raising an error. 479@end defvar 480 481@defopt before-save-hook 482This normal hook runs before a buffer is saved in its visited file, 483regardless of whether that is done normally or by one of the hooks 484described above. For instance, the @file{copyright.el} program uses 485this hook to make sure the file you are saving has the current year in 486its copyright notice. 487@end defopt 488 489@c Emacs 19 feature 490@defopt after-save-hook 491This normal hook runs after a buffer has been saved in its visited file. 492@end defopt 493 494@defopt file-precious-flag 495If this variable is non-@code{nil}, then @code{save-buffer} protects 496against I/O errors while saving by writing the new file to a temporary 497name instead of the name it is supposed to have, and then renaming it to 498the intended name after it is clear there are no errors. This procedure 499prevents problems such as a lack of disk space from resulting in an 500invalid file. 501 502As a side effect, backups are necessarily made by copying. @xref{Rename 503or Copy}. Yet, at the same time, saving a precious file always breaks 504all hard links between the file you save and other file names. 505 506Some modes give this variable a non-@code{nil} buffer-local value 507in particular buffers. 508@end defopt 509 510@defopt require-final-newline 511This variable determines whether files may be written out that do 512@emph{not} end with a newline. If the value of the variable is 513@code{t}, then @code{save-buffer} silently adds a newline at the end 514of the buffer whenever it does not already end in one. If the value 515is @code{visit}, Emacs adds a missing newline just after it visits the 516file. If the value is @code{visit-save}, Emacs adds a missing newline 517both on visiting and on saving. For any other non-@code{nil} value, 518@code{save-buffer} asks the user whether to add a newline each time 519the case arises. 520 521If the value of the variable is @code{nil}, then @code{save-buffer} 522doesn't add newlines at all. @code{nil} is the default value, but a few 523major modes set it to @code{t} in particular buffers. 524@end defopt 525 526 See also the function @code{set-visited-file-name} (@pxref{Buffer File 527Name}). 528 529@node Reading from Files 530@section Reading from Files 531@cindex reading from files 532 533 To copy the contents of a file into a buffer, use the function 534@code{insert-file-contents}. (Don't use the command 535@code{insert-file} in a Lisp program, as that sets the mark.) 536 537@defun insert-file-contents filename &optional visit beg end replace 538This function inserts the contents of file @var{filename} into the 539current buffer after point. It returns a list of the absolute file name 540and the length of the data inserted. An error is signaled if 541@var{filename} is not the name of a file that can be read. 542 543This function checks the file contents against the defined file 544formats, and converts the file contents if appropriate and also calls 545the functions in the list @code{after-insert-file-functions}. 546@xref{Format Conversion}. Normally, one of the functions in the 547@code{after-insert-file-functions} list determines the coding system 548(@pxref{Coding Systems}) used for decoding the file's contents, 549including end-of-line conversion. However, if the file contains null 550bytes, it is by default visited without any code conversions. 551@xref{Lisp and Coding Systems, inhibit-nul-byte-detection}. 552 553If @var{visit} is non-@code{nil}, this function additionally marks the 554buffer as unmodified and sets up various fields in the buffer so that it 555is visiting the file @var{filename}: these include the buffer's visited 556file name and its last save file modtime. This feature is used by 557@code{find-file-noselect} and you probably should not use it yourself. 558 559If @var{beg} and @var{end} are non-@code{nil}, they should be numbers 560that are byte offsets specifying the portion of the file to insert. 561In this case, @var{visit} must be @code{nil}. For example, 562 563@example 564(insert-file-contents filename nil 0 500) 565@end example 566 567@noindent 568inserts the first 500 characters of a file. 569 570If the argument @var{replace} is non-@code{nil}, it means to replace the 571contents of the buffer (actually, just the accessible portion) with the 572contents of the file. This is better than simply deleting the buffer 573contents and inserting the whole file, because (1) it preserves some 574marker positions and (2) it puts less data in the undo list. 575 576It is possible to read a special file (such as a FIFO or an I/O device) 577with @code{insert-file-contents}, as long as @var{replace} and 578@var{visit} are @code{nil}. 579@end defun 580 581@defun insert-file-contents-literally filename &optional visit beg end replace 582This function works like @code{insert-file-contents} except that it 583does not run @code{after-insert-file-functions}, and does not do 584format decoding, character code conversion, automatic uncompression, 585and so on. 586@end defun 587 588If you want to pass a file name to another process so that another 589program can read the file, use the function @code{file-local-copy}; see 590@ref{Magic File Names}. 591 592@node Writing to Files 593@section Writing to Files 594@cindex writing to files 595 596 You can write the contents of a buffer, or part of a buffer, directly 597to a file on disk using the @code{append-to-file} and 598@code{write-region} functions. Don't use these functions to write to 599files that are being visited; that could cause confusion in the 600mechanisms for visiting. 601 602@deffn Command append-to-file start end filename 603This function appends the contents of the region delimited by 604@var{start} and @var{end} in the current buffer to the end of file 605@var{filename}. If that file does not exist, it is created. This 606function returns @code{nil}. 607 608An error is signaled if you cannot write or create @var{filename}. 609 610When called from Lisp, this function is completely equivalent to: 611 612@example 613(write-region start end filename t) 614@end example 615@end deffn 616 617@deffn Command write-region start end filename &optional append visit lockname mustbenew 618This function writes the region delimited by @var{start} and @var{end} 619in the current buffer into the file specified by @var{filename}. 620 621If @var{start} is @code{nil}, then the command writes the entire buffer 622contents (@emph{not} just the accessible portion) to the file and 623ignores @var{end}. 624 625@c Emacs 19 feature 626If @var{start} is a string, then @code{write-region} writes or appends 627that string, rather than text from the buffer. @var{end} is ignored in 628this case. 629 630If @var{append} is non-@code{nil}, then the specified text is appended 631to the existing file contents (if any). If @var{append} is a 632number, @code{write-region} seeks to that byte offset from the start 633of the file and writes the data from there. 634 635If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks 636for confirmation if @var{filename} names an existing file. If 637@var{mustbenew} is the symbol @code{excl}, then @code{write-region} 638does not ask for confirmation, but instead it signals an error 639@code{file-already-exists} if the file already exists. Although 640@code{write-region} normally follows a symbolic link and creates the 641pointed-to file if the symbolic link is dangling, it does not follow 642symbolic links if @var{mustbenew} is @code{excl}. 643 644The test for an existing file, when @var{mustbenew} is @code{excl}, uses 645a special system feature. At least for files on a local disk, there is 646no chance that some other program could create a file of the same name 647before Emacs does, without Emacs's noticing. 648 649If @var{visit} is @code{t}, then Emacs establishes an association 650between the buffer and the file: the buffer is then visiting that file. 651It also sets the last file modification time for the current buffer to 652@var{filename}'s modtime, and marks the buffer as not modified. This 653feature is used by @code{save-buffer}, but you probably should not use 654it yourself. 655 656@c Emacs 19 feature 657If @var{visit} is a string, it specifies the file name to visit. This 658way, you can write the data to one file (@var{filename}) while recording 659the buffer as visiting another file (@var{visit}). The argument 660@var{visit} is used in the echo area message and also for file locking; 661@var{visit} is stored in @code{buffer-file-name}. This feature is used 662to implement @code{file-precious-flag}; don't use it yourself unless you 663really know what you're doing. 664 665The optional argument @var{lockname}, if non-@code{nil}, specifies the 666file name to use for purposes of locking and unlocking, overriding 667@var{filename} and @var{visit} for that purpose. 668 669The function @code{write-region} converts the data which it writes to 670the appropriate file formats specified by @code{buffer-file-format} 671and also calls the functions in the list 672@code{write-region-annotate-functions}. 673@xref{Format Conversion}. 674 675Normally, @code{write-region} displays the message @samp{Wrote 676@var{filename}} in the echo area. This message is inhibited if 677@var{visit} is neither @code{t} nor @code{nil} nor a string, or if 678Emacs is operating in batch mode (@pxref{Batch Mode}). This 679feature is useful for programs that use files for internal purposes, 680files that the user does not need to know about. 681@end deffn 682 683@defvar write-region-inhibit-fsync 684If this variable's value is @code{nil}, @code{write-region} uses the 685@code{fsync} system call after writing a file. Although this slows 686Emacs down, it lessens the risk of data loss after power failure. If 687the value is @code{t}, Emacs does not use @code{fsync}. The default 688value is @code{nil} when Emacs is interactive, and @code{t} when Emacs 689runs in batch mode. @xref{Files and Storage}. 690@end defvar 691 692@defmac with-temp-file file body@dots{} 693@anchor{Definition of with-temp-file} 694The @code{with-temp-file} macro evaluates the @var{body} forms with a 695temporary buffer as the current buffer; then, at the end, it writes the 696buffer contents into file @var{file}. It kills the temporary buffer 697when finished, restoring the buffer that was current before the 698@code{with-temp-file} form. Then it returns the value of the last form 699in @var{body}. 700 701The current buffer is restored even in case of an abnormal exit via 702@code{throw} or error (@pxref{Nonlocal Exits}). 703 704See also @code{with-temp-buffer} in @ref{Definition of 705with-temp-buffer,, The Current Buffer}. 706@end defmac 707 708@node File Locks 709@section File Locks 710@cindex file locks 711@cindex lock file 712@cindex .#, lock file names 713 714 When two users edit the same file at the same time, they are likely 715to interfere with each other. Emacs tries to prevent this situation 716from arising by recording a @dfn{file lock} when a file is being 717modified. 718Emacs can then detect the first attempt to modify a buffer visiting a 719file that is locked by another Emacs job, and ask the user what to do. 720The file lock is really a file, a symbolic link with a special name, 721stored in the same directory as the file you are editing. The name is 722constructed by prepending @file{.#} to the filename of the buffer. 723The target of the symbolic link will be of the form 724@code{@var{user}@@@var{host}.@var{pid}:@var{boot}}, where @var{user} 725is replaced with the current username (from @code{user-login-name}), 726@var{host} with the name of the host where Emacs is running (from 727@code{system-name}), @var{pid} with Emacs's process id, and @var{boot} 728with the time since the last reboot. @code{:@var{boot}} is omitted if 729the boot time is unavailable. (On file systems that do not support 730symbolic links, a regular file is used instead, with contents of the 731form @code{@var{user}@@@var{host}.@var{pid}:@var{boot}}.) 732 733 When you access files using NFS, there may be a small probability that 734you and another user will both lock the same file simultaneously. 735If this happens, it is possible for the two users to make changes 736simultaneously, but Emacs will still warn the user who saves second. 737Also, the detection of modification of a buffer visiting a file changed 738on disk catches some cases of simultaneous editing; see 739@ref{Modification Time}. 740 741@defun file-locked-p filename 742This function returns @code{nil} if the file @var{filename} is not 743locked. It returns @code{t} if it is locked by this Emacs process, and 744it returns the name of the user who has locked it if it is locked by 745some other job. 746 747@example 748@group 749(file-locked-p "foo") 750 @result{} nil 751@end group 752@end example 753@end defun 754 755@defun lock-buffer &optional filename 756This function locks the file @var{filename}, if the current buffer is 757modified. The argument @var{filename} defaults to the current buffer's 758visited file. Nothing is done if the current buffer is not visiting a 759file, or is not modified, or if the option @code{create-lockfiles} is 760@code{nil}. 761@end defun 762 763@defun unlock-buffer 764This function unlocks the file being visited in the current buffer, 765if the buffer is modified. If the buffer is not modified, then 766the file should not be locked, so this function does nothing. It also 767does nothing if the current buffer is not visiting a file, or is not locked. 768@end defun 769 770@defopt create-lockfiles 771If this variable is @code{nil}, Emacs does not lock files. 772@end defopt 773 774@defun ask-user-about-lock file other-user 775This function is called when the user tries to modify @var{file}, but it 776is locked by another user named @var{other-user}. The default 777definition of this function asks the user to say what to do. The value 778this function returns determines what Emacs does next: 779 780@itemize @bullet 781@item 782A value of @code{t} says to grab the lock on the file. Then 783this user may edit the file and @var{other-user} loses the lock. 784 785@item 786A value of @code{nil} says to ignore the lock and let this 787user edit the file anyway. 788 789@item 790@kindex file-locked 791This function may instead signal a @code{file-locked} error, in which 792case the change that the user was about to make does not take place. 793 794The error message for this error looks like this: 795 796@example 797@error{} File is locked: @var{file} @var{other-user} 798@end example 799 800@noindent 801where @code{file} is the name of the file and @var{other-user} is the 802name of the user who has locked the file. 803@end itemize 804 805If you wish, you can replace the @code{ask-user-about-lock} function 806with your own version that makes the decision in another way. 807@end defun 808 809@node Information about Files 810@section Information about Files 811@cindex file, information about 812 813 This section describes the functions for retrieving various types of 814information about files (or directories or symbolic links), such as 815whether a file is readable or writable, and its size. These functions 816all take arguments which are file names. Except where noted, these 817arguments need to specify existing files, or an error is signaled. 818 819@cindex file names, trailing whitespace 820@cindex trailing blanks in file names 821 Be careful with file names that end in spaces. On some filesystems 822(notably, MS-Windows), trailing whitespace characters in file names 823are silently and automatically ignored. 824 825@menu 826* Testing Accessibility:: Is a given file readable? Writable? 827* Kinds of Files:: Is it a directory? A symbolic link? 828* Truenames:: Eliminating symbolic links from a file name. 829* File Attributes:: File sizes, modification times, etc. 830* Extended Attributes:: Extended file attributes for access control. 831* Locating Files:: How to find a file in standard places. 832@end menu 833 834@node Testing Accessibility 835@subsection Testing Accessibility 836@cindex accessibility of a file 837@cindex file accessibility 838 839 These functions test for permission to access a file for reading, 840writing, or execution. Unless explicitly stated otherwise, they 841follow symbolic links. @xref{Kinds of Files}. 842 843 On some operating systems, more complex sets of access permissions 844can be specified, via mechanisms such as Access Control Lists (ACLs). 845@xref{Extended Attributes}, for how to query and set those 846permissions. 847 848@defun file-exists-p filename 849This function returns @code{t} if a file named @var{filename} appears 850to exist. This does not mean you can necessarily read the file, only 851that you can probably find out its attributes. (On GNU and other POSIX-like 852systems, this is true if the file exists and you have execute 853permission on the containing directories, regardless of the 854permissions of the file itself.) 855 856If the file does not exist, or if there was trouble determining 857whether the file exists, this function returns @code{nil}. 858 859Directories are files, so @code{file-exists-p} can return @code{t} when 860given a directory. However, because @code{file-exists-p} follows 861symbolic links, it returns @code{t} for a symbolic link 862name only if the target file exists. 863@end defun 864 865@defun file-readable-p filename 866This function returns @code{t} if a file named @var{filename} exists 867and you can read it. It returns @code{nil} otherwise. 868@end defun 869 870@defun file-executable-p filename 871This function returns @code{t} if a file named @var{filename} exists 872and you can execute it. It returns @code{nil} otherwise. On GNU and 873other POSIX-like systems, if the file is a directory, execute 874permission means you can check the existence and attributes of files 875inside the directory, and open those files if their modes permit. 876@end defun 877 878@defun file-writable-p filename 879This function returns @code{t} if the file @var{filename} can be written 880or created by you, and @code{nil} otherwise. A file is writable if the 881file exists and you can write it. It is creatable if it does not exist, 882but its parent directory does exist and you can write in that 883directory. 884 885In the example below, @file{foo} is not writable because the parent 886directory does not exist, even though the user could create such a 887directory. 888 889@example 890@group 891(file-writable-p "~/no-such-dir/foo") 892 @result{} nil 893@end group 894@end example 895@end defun 896 897@defun file-accessible-directory-p dirname 898This function returns @code{t} if you have permission to open existing 899files in the directory whose name as a file is @var{dirname}; 900otherwise (e.g., if there is no such directory), it returns @code{nil}. 901The value of @var{dirname} may be either a directory name (such as 902@file{/foo/}) or the file name of a file which is a directory 903(such as @file{/foo}, without the final slash). 904 905For example, from the following we deduce that any attempt to read a 906file in @file{/foo/} will give an error: 907 908@example 909(file-accessible-directory-p "/foo") 910 @result{} nil 911@end example 912@end defun 913 914@defun access-file filename string 915If you can read @var{filename} this function returns @code{nil}; 916otherwise it signals an error 917using @var{string} as the error message text. 918@end defun 919 920@defun file-ownership-preserved-p filename &optional group 921This function returns @code{t} if deleting the file @var{filename} and 922then creating it anew would keep the file's owner unchanged. It also 923returns @code{t} for nonexistent files. 924 925If the optional argument @var{group} is non-@code{nil}, this function 926also checks that the file's group would be unchanged. 927 928This function does not follow symbolic links. 929@end defun 930 931@defun file-modes filename 932@cindex mode bits 933@cindex file permissions 934@cindex permissions, file 935@cindex file modes 936This function returns the @dfn{mode bits} of @var{filename}---an 937integer summarizing its read, write, and execution permissions. 938This function follows symbolic links. If the file does not exist, the 939return value is @code{nil}. 940 941@xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils} 942Manual}, for a description of mode bits. For example, if the 943low-order bit is 1, the file is executable by all users; if the 944second-lowest-order bit is 1, the file is writable by all users; etc. 945The highest possible value is 4095 (7777 octal), meaning that everyone 946has read, write, and execute permission, the @acronym{SUID} bit is set 947for both others and group, and the sticky bit is set. 948 949@xref{Changing Files}, for the @code{set-file-modes} function, which 950can be used to set these permissions. 951 952@example 953@group 954(file-modes "~/junk/diffs") 955 @result{} 492 ; @r{Decimal integer.} 956@end group 957@group 958(format "%o" 492) 959 @result{} "754" ; @r{Convert to octal.} 960@end group 961 962@group 963(set-file-modes "~/junk/diffs" #o666) 964 @result{} nil 965@end group 966 967@group 968$ ls -l diffs 969-rw-rw-rw- 1 lewis lewis 3063 Oct 30 16:00 diffs 970@end group 971@end example 972 973@cindex MS-DOS and file modes 974@cindex file modes and MS-DOS 975@strong{MS-DOS note:} On MS-DOS, there is no such thing as an 976executable file mode bit. So @code{file-modes} considers a file 977executable if its name ends in one of the standard executable 978extensions, such as @file{.com}, @file{.bat}, @file{.exe}, and some 979others. Files that begin with the POSIX-standard @samp{#!} signature, 980such as shell and Perl scripts, are also considered executable. 981Directories are also reported as executable, for compatibility with 982POSIX@. These conventions are also followed by @code{file-attributes} 983(@pxref{File Attributes}). 984@end defun 985 986@node Kinds of Files 987@subsection Distinguishing Kinds of Files 988@cindex file classification 989@cindex classification of file types 990@cindex symbolic links 991 992 This section describes how to distinguish various kinds of files, such 993as directories, symbolic links, and ordinary files. 994 995 Symbolic links are ordinarily followed wherever they appear. For 996example, to interpret the file name @file{a/b/c}, any of @file{a}, 997@file{a/b}, and @file{a/b/c} can be symbolic links that are followed, 998possibly recursively if the link targets are themselves symbolic 999links. However, a few functions do not follow symbolic links at the 1000end of a file name (@file{a/b/c} in this example). Such a function 1001is said to @dfn{not follow symbolic links}. 1002 1003@defun file-symlink-p filename 1004@cindex symbolic links 1005If the file @var{filename} is a symbolic link, this function does not 1006follow it and instead returns its link target 1007as a string. (The link target string is not necessarily the full 1008absolute file name of the target; determining the full file name that 1009the link points to is nontrivial, see below.) 1010 1011If the file @var{filename} is not a symbolic link, or does not exist, 1012or if there is trouble determining whether it is a symbolic link, 1013@code{file-symlink-p} returns @code{nil}. 1014 1015Here are a few examples of using this function: 1016 1017@example 1018@group 1019(file-symlink-p "not-a-symlink") 1020 @result{} nil 1021@end group 1022@group 1023(file-symlink-p "sym-link") 1024 @result{} "not-a-symlink" 1025@end group 1026@group 1027(file-symlink-p "sym-link2") 1028 @result{} "sym-link" 1029@end group 1030@group 1031(file-symlink-p "/bin") 1032 @result{} "/pub/bin" 1033@end group 1034@end example 1035 1036Note that in the third example, the function returned @file{sym-link}, 1037but did not proceed to resolve it, although that file is itself a 1038symbolic link. That is because this function does not follow symbolic 1039links---the process of following the symbolic links does not apply to 1040the last component of the file name. 1041 1042The string that this function returns is what is recorded in the 1043symbolic link; it may or may not include any leading directories. 1044This function does @emph{not} expand the link target to produce a 1045fully-qualified file name, and in particular does not use the leading 1046directories, if any, of the @var{filename} argument if the link target 1047is not an absolute file name. Here's an example: 1048 1049@example 1050@group 1051(file-symlink-p "/foo/bar/baz") 1052 @result{} "some-file" 1053@end group 1054@end example 1055 1056@noindent 1057Here, although @file{/foo/bar/baz} was given as a fully-qualified file 1058name, the result is not, and in fact does not have any leading 1059directories at all. And since @file{some-file} might itself be a 1060symbolic link, you cannot simply prepend leading directories to it, 1061nor even naively use @code{expand-file-name} (@pxref{File Name 1062Expansion}) to produce its absolute file name. 1063 1064For this reason, this function is seldom useful if you need to 1065determine more than just the fact that a file is or isn't a symbolic 1066link. If you actually need the file name of the link target, use 1067@code{file-chase-links} or @code{file-truename}, described in 1068@ref{Truenames}. 1069@end defun 1070 1071@defun file-directory-p filename 1072This function returns @code{t} if @var{filename} is the name of an 1073existing directory. It returns @code{nil} if @var{filename} does 1074not name a directory, or if there is trouble determining whether 1075it is a directory. 1076This function follows symbolic links. 1077 1078@example 1079@group 1080(file-directory-p "~rms") 1081 @result{} t 1082@end group 1083@group 1084(file-directory-p "~rms/lewis/files.texi") 1085 @result{} nil 1086@end group 1087@group 1088(file-directory-p "~rms/lewis/no-such-file") 1089 @result{} nil 1090@end group 1091@group 1092(file-directory-p "$HOME") 1093 @result{} nil 1094@end group 1095@group 1096(file-directory-p 1097 (substitute-in-file-name "$HOME")) 1098 @result{} t 1099@end group 1100@end example 1101@end defun 1102 1103@defun file-regular-p filename 1104This function returns @code{t} if the file @var{filename} exists and is 1105a regular file (not a directory, named pipe, terminal, or 1106other I/O device). 1107It returns @code{nil} if @var{filename} does not exist or is not a regular 1108file, or if there is trouble determining whether it is a regular file. 1109This function follows symbolic links. 1110@end defun 1111 1112@node Truenames 1113@subsection Truenames 1114@cindex truename (of file) 1115 1116 The @dfn{truename} of a file is the name that you get by following 1117symbolic links at all levels until none remain, then simplifying away 1118@samp{.}@: and @samp{..}@: appearing as name components. This results 1119in a sort of canonical name for the file. A file does not always have a 1120unique truename; the number of distinct truenames a file has is equal to 1121the number of hard links to the file. However, truenames are useful 1122because they eliminate symbolic links as a cause of name variation. 1123 1124@defun file-truename filename 1125This function returns the truename of the file @var{filename}. If the 1126argument is not an absolute file name, this function first expands it 1127against @code{default-directory}. 1128 1129This function does not expand environment variables. Only 1130@code{substitute-in-file-name} does that. @xref{Definition of 1131substitute-in-file-name}. 1132 1133If you may need to follow symbolic links preceding @samp{..}@: 1134appearing as a name component, call @code{file-truename} without prior 1135direct or indirect calls to @code{expand-file-name}. Otherwise, the 1136file name component immediately preceding @samp{..} will be 1137simplified away before @code{file-truename} is called. To 1138eliminate the need for a call to @code{expand-file-name}, 1139@code{file-truename} handles @samp{~} in the same way that 1140@code{expand-file-name} does. 1141 1142If the target of a symbolic links has remote file name syntax, 1143@code{file-truename} returns it quoted. @xref{File Name Expansion,, 1144Functions that Expand Filenames}. 1145@end defun 1146 1147@defun file-chase-links filename &optional limit 1148This function follows symbolic links, starting with @var{filename}, 1149until it finds a file name which is not the name of a symbolic link. 1150Then it returns that file name. This function does @emph{not} follow 1151symbolic links at the level of parent directories. 1152 1153If you specify a number for @var{limit}, then after chasing through 1154that many links, the function just returns what it has even if that is 1155still a symbolic link. 1156@end defun 1157 1158 To illustrate the difference between @code{file-chase-links} and 1159@code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to 1160the directory @file{/home/foo}, and @file{/home/foo/hello} is an 1161ordinary file (or at least, not a symbolic link) or nonexistent. Then 1162we would have: 1163 1164@example 1165(file-chase-links "/usr/foo/hello") 1166 ;; @r{This does not follow the links in the parent directories.} 1167 @result{} "/usr/foo/hello" 1168(file-truename "/usr/foo/hello") 1169 ;; @r{Assuming that @file{/home} is not a symbolic link.} 1170 @result{} "/home/foo/hello" 1171@end example 1172 1173@defun file-equal-p file1 file2 1174This function returns @code{t} if the files @var{file1} and 1175@var{file2} name the same file. This is similar to comparing their 1176truenames, except that remote file names are also handled in an 1177appropriate manner. If @var{file1} or @var{file2} does not exist, the 1178return value is unspecified. 1179@end defun 1180 1181@defun file-name-case-insensitive-p filename 1182Sometimes file names or their parts need to be compared as strings, in 1183which case it's important to know whether the underlying filesystem is 1184case-insensitive. This function returns @code{t} if file 1185@var{filename} is on a case-insensitive filesystem. It always returns 1186@code{t} on MS-DOS and MS-Windows. On Cygwin and macOS, 1187filesystems may or may not be case-insensitive, and the function tries 1188to determine case-sensitivity by a runtime test. If the test is 1189inconclusive, the function returns @code{t} on Cygwin and @code{nil} 1190on macOS. 1191 1192Currently this function always returns @code{nil} on platforms other 1193than MS-DOS, MS-Windows, Cygwin, and macOS@. It does not detect 1194case-insensitivity of mounted filesystems, such as Samba shares or 1195NFS-mounted Windows volumes. On remote hosts, it assumes @code{t} for 1196the @samp{smb} method. For all other connection methods, runtime 1197tests are performed. 1198@end defun 1199 1200@defun file-in-directory-p file dir 1201This function returns @code{t} if @var{file} is a file in directory 1202@var{dir}, or in a subdirectory of @var{dir}. It also returns 1203@code{t} if @var{file} and @var{dir} are the same directory. It 1204compares the truenames of the two directories. If @var{dir} does not 1205name an existing directory, the return value is @code{nil}. 1206@end defun 1207 1208@defun vc-responsible-backend file 1209This function determines the responsible VC backend of the given 1210@var{file}. For example, if @file{emacs.c} is a file tracked by Git, 1211@w{@code{(vc-responsible-backend "emacs.c")}} returns @samp{Git}. 1212Note that if @var{file} is a symbolic link, 1213@code{vc-responsible-backend} will not resolve it---the backend of the 1214symbolic link file itself is reported. To get the backend VC of the 1215file to which @var{file} refers, wrap @var{file} with a symbolic link 1216resolving function such as @code{file-chase-links}: 1217 1218@smallexample 1219(vc-responsible-backend (file-chase-links "emacs.c")) 1220@end smallexample 1221@end defun 1222 1223@node File Attributes 1224@subsection File Attributes 1225@cindex file attributes 1226 1227 This section describes the functions for getting detailed 1228information about a file, including the owner and group numbers, the 1229number of names, the inode number, the size, and the times of access 1230and modification. 1231 1232@defun file-newer-than-file-p filename1 filename2 1233@cindex file age 1234@cindex file modification time 1235This function returns @code{t} if the file @var{filename1} is 1236newer than file @var{filename2}. If @var{filename1} does not 1237exist, it returns @code{nil}. If @var{filename1} does exist, but 1238@var{filename2} does not, it returns @code{t}. 1239 1240In the following example, assume that the file @file{aug-19} was written 1241on the 19th, @file{aug-20} was written on the 20th, and the file 1242@file{no-file} doesn't exist at all. 1243 1244@example 1245@group 1246(file-newer-than-file-p "aug-19" "aug-20") 1247 @result{} nil 1248@end group 1249@group 1250(file-newer-than-file-p "aug-20" "aug-19") 1251 @result{} t 1252@end group 1253@group 1254(file-newer-than-file-p "aug-19" "no-file") 1255 @result{} t 1256@end group 1257@group 1258(file-newer-than-file-p "no-file" "aug-19") 1259 @result{} nil 1260@end group 1261@end example 1262@end defun 1263 1264@defun file-attributes filename &optional id-format 1265@anchor{Definition of file-attributes} 1266This function returns a list of attributes of file @var{filename}. If 1267the specified file does not exist, it returns @code{nil}. 1268This function does not follow symbolic links. 1269The optional parameter @var{id-format} specifies the preferred format 1270of attributes @acronym{UID} and @acronym{GID} (see below)---the 1271valid values are @code{'string} and @code{'integer}. The latter is 1272the default, but we plan to change that, so you should specify a 1273non-@code{nil} value for @var{id-format} if you use the returned 1274@acronym{UID} or @acronym{GID}. 1275 1276On GNU platforms when operating on a local file, this function is 1277atomic: if the filesystem is simultaneously being changed by some 1278other process, this function returns the file's attributes either 1279before or after the change. Otherwise this function is not atomic, 1280and might return @code{nil} if it detects the race condition, or might 1281return a hodgepodge of the previous and current file attributes. 1282 1283Accessor functions are provided to access the elements in this list. 1284The accessors are mentioned along with the descriptions of the 1285elements below. 1286 1287The elements of the list, in order, are: 1288 1289@enumerate 0 1290@item 1291@code{t} for a directory, a string for a symbolic link (the name 1292linked to), or @code{nil} for a text file 1293(@code{file-attribute-type}). 1294 1295@c Wordy so as to prevent an overfull hbox. --rjc 15mar92 1296@item 1297The number of names the file has (@code{file-attribute-link-number}). 1298Alternate names, also known as hard links, can be created by using the 1299@code{add-name-to-file} function (@pxref{Changing Files}). 1300 1301@item 1302The file's @acronym{UID}, normally as a string 1303(@code{file-attribute-user-id}). However, if it does not correspond 1304to a named user, the value is an integer. 1305 1306@item 1307The file's @acronym{GID}, likewise (@code{file-attribute-group-id}). 1308 1309@item 1310The time of last access as a Lisp timestamp 1311(@code{file-attribute-access-time}). The timestamp is in the 1312style of @code{current-time} (@pxref{Time of Day}) and is truncated 1313to that of the filesystem's timestamp resolution; for example, on some 1314FAT-based filesystems, only the date of last access is recorded, so 1315this time will always hold the midnight of the day of the last access. 1316 1317@cindex modification time of file 1318@item 1319The time of last modification as a Lisp timestamp 1320(@code{file-attribute-modification-time}). This is the last time when 1321the file's contents were modified. 1322 1323@item 1324The time of last status change as a Lisp timestamp 1325(@code{file-attribute-status-change-time}). This is the time of the 1326last change to the file's access mode bits, its owner and group, and 1327other information recorded in the filesystem for the file, beyond the 1328file's contents. 1329 1330@item 1331The size of the file in bytes (@code{file-attribute-size}). 1332 1333@item 1334The file's modes, as a string of ten letters or dashes, as in 1335@samp{ls -l} (@code{file-attribute-modes}). 1336 1337@item 1338An unspecified value, present for backward compatibility. 1339 1340@item 1341The file's inode number (@code{file-attribute-inode-number}), 1342a nonnegative integer. 1343 1344@item 1345The filesystem number of the device that the file is on 1346@code{file-attribute-device-number}), an integer. 1347This element and the file's inode number 1348together give enough information to distinguish any two files on the 1349system---no two files can have the same values for both of these 1350numbers. 1351@end enumerate 1352 1353For example, here are the file attributes for @file{files.texi}: 1354 1355@example 1356@group 1357(file-attributes "files.texi" 'string) 1358 @result{} (nil 1 "lh" "users" 1359 (20614 64019 50040 152000) 1360 (20000 23 0 0) 1361 (20614 64555 902289 872000) 1362 122295 "-rw-rw-rw-" 1363 t 6473924464520138 1364 1014478468) 1365@end group 1366@end example 1367 1368@noindent 1369and here is how the result is interpreted: 1370 1371@table @code 1372@item nil 1373is neither a directory nor a symbolic link. 1374 1375@item 1 1376has only one name (the name @file{files.texi} in the current default 1377directory). 1378 1379@item "lh" 1380is owned by the user with name @samp{lh}. 1381 1382@item "users" 1383is in the group with name @samp{users}. 1384 1385@item (20614 64019 50040 152000) 1386was last accessed on October 23, 2012, at 20:12:03.050040152 UTC. 1387 1388@item (20000 23 0 0) 1389was last modified on July 15, 2001, at 08:53:43 UTC. 1390 1391@item (20614 64555 902289 872000) 1392last had its status changed on October 23, 2012, at 20:20:59.902289872 UTC. 1393 1394@item 122295 1395is 122295 bytes long. (It may not contain 122295 characters, though, 1396if some of the bytes belong to multibyte sequences, and also if the 1397end-of-line format is CR-LF.) 1398 1399@item "-rw-rw-rw-" 1400has a mode of read and write access for the owner, group, and world. 1401 1402@item t 1403is merely a placeholder; it carries no information. 1404 1405@item 6473924464520138 1406has an inode number of 6473924464520138. 1407 1408@item 1014478468 1409is on the file-system device whose number is 1014478468. 1410@end table 1411@end defun 1412 1413@defun file-nlinks filename 1414This function returns the number of names (i.e., hard links) that 1415file @var{filename} has. If the file does not exist, this function 1416returns @code{nil}. Note that symbolic links have no effect on this 1417function, because they are not considered to be names of the files 1418they link to. This function does not follow symbolic links. 1419 1420@example 1421@group 1422$ ls -l foo* 1423-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo 1424-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1 1425@end group 1426 1427@group 1428(file-nlinks "foo") 1429 @result{} 2 1430@end group 1431@group 1432(file-nlinks "doesnt-exist") 1433 @result{} nil 1434@end group 1435@end example 1436@end defun 1437 1438@node Extended Attributes 1439@subsection Extended File Attributes 1440@cindex extended file attributes 1441 1442On some operating systems, each file can be associated with arbitrary 1443@dfn{extended file attributes}. At present, Emacs supports querying 1444and setting two specific sets of extended file attributes: Access 1445Control Lists (ACLs) and SELinux contexts. These extended file 1446attributes are used, on some systems, to impose more sophisticated 1447file access controls than the basic Unix-style permissions 1448discussed in the previous sections. 1449 1450@cindex access control list 1451@cindex ACL entries 1452@cindex SELinux context 1453 A detailed explanation of ACLs and SELinux is beyond the scope of 1454this manual. For our purposes, each file can be associated with an 1455@dfn{ACL}, which specifies its properties under an ACL-based file 1456control system, and/or an @dfn{SELinux context}, which specifies its 1457properties under the SELinux system. 1458 1459@defun file-acl filename 1460This function returns the ACL for the file @var{filename}. The exact 1461Lisp representation of the ACL is unspecified (and may change in 1462future Emacs versions), but it is the same as what @code{set-file-acl} 1463takes for its @var{acl} argument (@pxref{Changing Files}). 1464 1465The underlying ACL implementation is platform-specific; on GNU/Linux 1466and BSD, Emacs uses the POSIX ACL interface, while on MS-Windows Emacs 1467emulates the POSIX ACL interface with native file security APIs. 1468 1469If ACLs are not supported or the file does not exist, 1470then the return value is @code{nil}. 1471@end defun 1472 1473@defun file-selinux-context filename 1474This function returns the SELinux context of the file @var{filename}, 1475as a list of the form @code{(@var{user} @var{role} @var{type} 1476@var{range})}. The list elements are the context's user, role, type, 1477and range respectively, as Lisp strings; see the SELinux documentation 1478for details about what these actually mean. The return value has the 1479same form as what @code{set-file-selinux-context} takes for its 1480@var{context} argument (@pxref{Changing Files}). 1481 1482If SELinux is not supported or the file does not exist, 1483then the return value is @code{(nil nil nil nil)}. 1484@end defun 1485 1486@defun file-extended-attributes filename 1487This function returns an alist of the Emacs-recognized extended 1488attributes of file @var{filename}. Currently, it serves as a 1489convenient way to retrieve both the ACL and SELinux context; you can 1490then call the function @code{set-file-extended-attributes}, with the 1491returned alist as its second argument, to apply the same file access 1492attributes to another file (@pxref{Changing Files}). 1493 1494One of the elements is @code{(acl . @var{acl})}, where @var{acl} has 1495the same form returned by @code{file-acl}. 1496 1497Another element is @code{(selinux-context . @var{context})}, where 1498@var{context} is the SELinux context, in the same form returned by 1499@code{file-selinux-context}. 1500@end defun 1501 1502@node Locating Files 1503@subsection Locating Files in Standard Places 1504@cindex locate file in path 1505@cindex find file in path 1506 1507 This section explains how to search for a file in a list of 1508directories (a @dfn{path}), or for an executable file in the standard 1509list of executable file directories. 1510 1511 To search for a user-specific configuration file, @xref{Standard 1512File Names}, for the @code{locate-user-emacs-file} function. 1513 1514@defun locate-file filename path &optional suffixes predicate 1515This function searches for a file whose name is @var{filename} in a 1516list of directories given by @var{path}, trying the suffixes in 1517@var{suffixes}. If it finds such a file, it returns the file's 1518absolute file name (@pxref{Relative File Names}); otherwise it returns 1519@code{nil}. 1520 1521The optional argument @var{suffixes} gives the list of file-name 1522suffixes to append to @var{filename} when searching. 1523@code{locate-file} tries each possible directory with each of these 1524suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there 1525are no suffixes, and @var{filename} is used only as-is. Typical 1526values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess 1527Creation}), @code{load-suffixes}, @code{load-file-rep-suffixes} and 1528the return value of the function @code{get-load-suffixes} (@pxref{Load 1529Suffixes}). 1530 1531Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess 1532Creation}) when looking for executable programs, or @code{load-path} 1533(@pxref{Library Search}) when looking for Lisp files. If 1534@var{filename} is absolute, @var{path} has no effect, but the suffixes 1535in @var{suffixes} are still tried. 1536 1537The optional argument @var{predicate}, if non-@code{nil}, specifies a 1538predicate function for testing whether a candidate file is suitable. 1539The predicate is passed the candidate file name as its single 1540argument. If @var{predicate} is @code{nil} or omitted, 1541@code{locate-file} uses @code{file-readable-p} as the predicate. 1542@xref{Kinds of Files}, for other useful predicates, e.g., 1543@code{file-executable-p} and @code{file-directory-p}. 1544 1545This function will normally skip directories, so if you want it to 1546find directories, make sure the @var{predicate} function returns 1547@code{dir-ok} for them. For example: 1548 1549@example 1550(locate-file "html" '("/var/www" "/srv") nil 1551 (lambda (f) (if (file-directory-p f) 'dir-ok))) 1552@end example 1553 1554 1555For compatibility, @var{predicate} can also be one of the symbols 1556@code{executable}, @code{readable}, @code{writable}, @code{exists}, or 1557a list of one or more of these symbols. 1558@end defun 1559 1560@defun executable-find program &optional remote 1561This function searches for the executable file of the named 1562@var{program} and returns the absolute file name of the executable, 1563including its file-name extensions, if any. It returns @code{nil} if 1564the file is not found. The function searches in all the directories 1565in @code{exec-path}, and tries all the file-name extensions in 1566@code{exec-suffixes} (@pxref{Subprocess Creation}). 1567 1568If @var{remote} is non-@code{nil}, and @code{default-directory} is a 1569remote directory, @var{program} is searched on the respective remote host. 1570@end defun 1571 1572@node Changing Files 1573@section Changing File Names and Attributes 1574@c @cindex renaming files Duplicates rename-file 1575@cindex copying files 1576@cindex deleting files 1577@cindex linking files 1578@cindex setting modes of files 1579 1580 The functions in this section rename, copy, delete, link, and set 1581the modes (permissions) of files. Typically, they signal a 1582@code{file-error} error if they fail to perform their function, 1583reporting the system-dependent error message that describes the reason 1584for the failure. If they fail because a file is missing, they signal 1585a @code{file-missing} error instead. 1586 1587 For performance, the operating system may cache or alias changes 1588made by these functions instead of writing them immediately to 1589secondary storage. @xref{Files and Storage}. 1590 1591 In the functions that have an argument @var{newname}, if this 1592argument is a directory name it is treated as if the nondirectory part 1593of the source name were appended. Typically, a directory name is one 1594that ends in @samp{/} (@pxref{Directory Names}). For example, if the 1595old name is @file{a/b/c}, the @var{newname} @file{d/e/f/} is treated 1596as if it were @file{d/e/f/c}. This special treatment does not apply 1597if @var{newname} is not a directory name but names a file that is a 1598directory; for example, the @var{newname} @file{d/e/f} is left as-is 1599even if @file{d/e/f} happens to be a directory. 1600 1601 In the functions that have an argument @var{newname}, if a file by the 1602name of @var{newname} already exists, the actions taken depend on the 1603value of the argument @var{ok-if-already-exists}: 1604 1605@itemize @bullet 1606@item 1607Signal a @code{file-already-exists} error if 1608@var{ok-if-already-exists} is @code{nil}. 1609 1610@item 1611Request confirmation if @var{ok-if-already-exists} is a number. 1612 1613@item 1614Replace the old file without confirmation if @var{ok-if-already-exists} 1615is any other value. 1616@end itemize 1617 1618@deffn Command add-name-to-file oldname newname &optional ok-if-already-exists 1619@cindex file with multiple names 1620@cindex file hard link 1621This function gives the file named @var{oldname} the additional name 1622@var{newname}. This means that @var{newname} becomes a new hard 1623link to @var{oldname}. 1624 1625If @var{newname} is a symbolic link, its directory entry is replaced, 1626not the directory entry it points to. If @var{oldname} is a symbolic 1627link, this function might or might not follow the link; it does not 1628follow the link on GNU platforms. If @var{oldname} is a directory, 1629this function typically fails, although for the superuser on a few 1630old-fashioned non-GNU platforms it can succeed and create a filesystem 1631that is not tree-structured. 1632 1633In the first part of the following example, we list two files, 1634@file{foo} and @file{foo3}. 1635 1636@example 1637@group 1638$ ls -li fo* 163981908 -rw-rw-rw- 1 rms rms 29 Aug 18 20:32 foo 164084302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3 1641@end group 1642@end example 1643 1644Now we create a hard link, by calling @code{add-name-to-file}, then list 1645the files again. This shows two names for one file, @file{foo} and 1646@file{foo2}. 1647 1648@example 1649@group 1650(add-name-to-file "foo" "foo2") 1651 @result{} nil 1652@end group 1653 1654@group 1655$ ls -li fo* 165681908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo 165781908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo2 165884302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3 1659@end group 1660@end example 1661 1662Finally, we evaluate the following: 1663 1664@example 1665(add-name-to-file "foo" "foo3" t) 1666@end example 1667 1668@noindent 1669and list the files again. Now there are three names 1670for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old 1671contents of @file{foo3} are lost. 1672 1673@example 1674@group 1675(add-name-to-file "foo1" "foo3") 1676 @result{} nil 1677@end group 1678 1679@group 1680$ ls -li fo* 168181908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo 168281908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo2 168381908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo3 1684@end group 1685@end example 1686 1687This function is meaningless on operating systems where multiple names 1688for one file are not allowed. Some systems implement multiple names 1689by copying the file instead. 1690 1691See also @code{file-nlinks} in @ref{File Attributes}. 1692@end deffn 1693 1694@deffn Command rename-file filename newname &optional ok-if-already-exists 1695This command renames the file @var{filename} as @var{newname}. 1696 1697If @var{filename} has additional names aside from @var{filename}, it 1698continues to have those names. In fact, adding the name @var{newname} 1699with @code{add-name-to-file} and then deleting @var{filename} has the 1700same effect as renaming, aside from momentary intermediate states and 1701treatment of errors, directories and symbolic links. 1702 1703This command does not follow symbolic links. If @var{filename} is a 1704symbolic link, this command renames the symbolic link, not the file it 1705points to. If @var{newname} is a symbolic link, its directory entry 1706is replaced, not the directory entry it points to. 1707 1708This command does nothing if @var{filename} and @var{newname} are the 1709same directory entry, i.e., if they refer to the same parent directory 1710and give the same name within that directory. Otherwise, if 1711@var{filename} and @var{newname} name the same file, this command does 1712nothing on POSIX-conforming systems, and removes @var{filename} on 1713some non-POSIX systems. 1714 1715If @var{newname} exists, then it must be an empty directory if 1716@var{oldname} is a directory and a non-directory otherwise. 1717@end deffn 1718 1719@deffn Command copy-file oldname newname &optional ok-if-already-exists time preserve-uid-gid preserve-extended-attributes 1720This command copies the file @var{oldname} to @var{newname}. An 1721error is signaled if @var{oldname} is not a regular file. If @var{newname} 1722names a directory, it copies @var{oldname} into that directory, 1723preserving its final name component. 1724@c FIXME: See Bug#27986 for how the previous sentence might change. 1725 1726This function follows symbolic links, except that it does not follow a 1727dangling symbolic link to create @var{newname}. 1728 1729If @var{time} is non-@code{nil}, then this function gives the new file 1730the same last-modified time that the old one has. (This works on only 1731some operating systems.) If setting the time gets an error, 1732@code{copy-file} signals a @code{file-date-error} error. In an 1733interactive call, a prefix argument specifies a non-@code{nil} value 1734for @var{time}. 1735 1736If argument @var{preserve-uid-gid} is @code{nil}, we let the operating 1737system decide the user and group ownership of the new file (this is 1738usually set to the user running Emacs). If @var{preserve-uid-gid} is 1739non-@code{nil}, we attempt to copy the user and group ownership of the 1740file. This works only on some operating systems, and only if you have 1741the correct permissions to do so. 1742 1743If the optional argument @var{preserve-permissions} is non-@code{nil}, 1744this function copies the file modes (or ``permissions'') of 1745@var{oldname} to @var{newname}, as well as the Access Control List and 1746SELinux context (if any). @xref{Information about Files}. 1747 1748Otherwise, the file modes of @var{newname} are left unchanged if it is 1749an existing file, and set to those of @var{oldname}, masked by the 1750default file permissions (see @code{set-default-file-modes} below), if 1751@var{newname} is to be newly created. The Access Control List or 1752SELinux context are not copied over in either case. 1753@end deffn 1754 1755@deffn Command make-symbolic-link target linkname &optional ok-if-already-exists 1756@pindex ln 1757@kindex file-already-exists 1758This command makes a symbolic link to @var{target}, named 1759@var{linkname}. This is like the shell command @samp{ln -s 1760@var{target} @var{linkname}}. The @var{target} argument 1761is treated only as a string; it need not name an existing file. 1762If @var{ok-if-already-exists} is an integer, indicating interactive 1763use, then leading @samp{~} is expanded and leading @samp{/:} is 1764stripped in the @var{target} string. 1765 1766If @var{target} is a relative file name, the resulting symbolic link 1767is interpreted relative to the directory containing the symbolic link. 1768@xref{Relative File Names}. 1769 1770If both @var{target} and @var{linkname} have remote file name syntax, 1771and if both remote identifications are equal, the symbolic link points 1772to the local file name part of @var{target}. 1773 1774This function is not available on systems that don't support symbolic 1775links. 1776@end deffn 1777 1778@cindex trash 1779@vindex delete-by-moving-to-trash 1780@deffn Command delete-file filename &optional trash 1781@pindex rm 1782This command deletes the file @var{filename}. If the file has 1783multiple names, it continues to exist under the other names. If 1784@var{filename} is a symbolic link, @code{delete-file} deletes only the 1785symbolic link and not its target. 1786 1787A suitable kind of @code{file-error} error is signaled if the file 1788does not exist, or is not deletable. (On GNU and other POSIX-like 1789systems, a file is deletable if its directory is writable.) 1790 1791If the optional argument @var{trash} is non-@code{nil} and the 1792variable @code{delete-by-moving-to-trash} is non-@code{nil}, this 1793command moves the file into the system Trash instead of deleting it. 1794@xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU 1795Emacs Manual}. When called interactively, @var{trash} is @code{t} if 1796no prefix argument is given, and @code{nil} otherwise. 1797 1798See also @code{delete-directory} in @ref{Create/Delete Dirs}. 1799@end deffn 1800 1801@cindex file permissions, setting 1802@cindex permissions, file 1803@cindex file modes, setting 1804@deffn Command set-file-modes filename mode 1805This function sets the @dfn{file mode} (or @dfn{permissions}) of 1806@var{filename} to @var{mode}. This function follows symbolic links. 1807 1808If called non-interactively, @var{mode} must be an integer. Only the 1809lowest 12 bits of the integer are used; on most systems, only the 1810lowest 9 bits are meaningful. You can use the Lisp construct for 1811octal numbers to enter @var{mode}. For example, 1812 1813@example 1814(set-file-modes #o644) 1815@end example 1816 1817@noindent 1818specifies that the file should be readable and writable for its owner, 1819readable for group members, and readable for all other users. 1820@xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils} 1821Manual}, for a description of mode bit specifications. 1822 1823Interactively, @var{mode} is read from the minibuffer using 1824@code{read-file-modes} (see below), which lets the user type in either 1825an integer or a string representing the permissions symbolically. 1826 1827@xref{File Attributes}, for the function @code{file-modes}, which 1828returns the permissions of a file. 1829@end deffn 1830 1831@defun set-default-file-modes mode 1832@cindex umask 1833This function sets the default permissions for new files created by 1834Emacs and its subprocesses. Every file created with Emacs initially 1835has these permissions, or a subset of them (@code{write-region} will 1836not grant execute permissions even if the default file permissions 1837allow execution). On GNU and other POSIX-like systems, the default 1838permissions are given by the bitwise complement of the @samp{umask} 1839value, i.e.@: each bit that is set in the argument @var{mode} will be 1840@emph{reset} in the default permissions with which Emacs creates 1841files. 1842 1843The argument @var{mode} should be an integer which specifies the 1844permissions, similar to @code{set-file-modes} above. Only the lowest 18459 bits are meaningful. 1846 1847The default file permissions have no effect when you save a modified 1848version of an existing file; saving a file preserves its existing 1849permissions. 1850@end defun 1851 1852@defmac with-file-modes mode body@dots{} 1853This macro evaluates the @var{body} forms with the default 1854permissions for new files temporarily set to @var{modes} (whose value 1855is as for @code{set-file-modes} above). When finished, it restores 1856the original default file permissions, and returns the value of the 1857last form in @var{body}. 1858 1859This is useful for creating private files, for example. 1860@end defmac 1861 1862@defun default-file-modes 1863This function returns the default file permissions, as an integer. 1864@end defun 1865 1866@defun read-file-modes &optional prompt base-file 1867This function reads a set of file mode bits from the minibuffer. The 1868first optional argument @var{prompt} specifies a non-default prompt. 1869Second second optional argument @var{base-file} is the name of a file 1870on whose permissions to base the mode bits that this function returns, 1871if what the user types specifies mode bits relative to permissions of 1872an existing file. 1873 1874If user input represents an octal number, this function returns that 1875number. If it is a complete symbolic specification of mode bits, as 1876in @code{"u=rwx"}, the function converts it to the equivalent numeric 1877value using @code{file-modes-symbolic-to-number} and returns the 1878result. If the specification is relative, as in @code{"o+g"}, then 1879the permissions on which the specification is based are taken from the 1880mode bits of @var{base-file}. If @var{base-file} is omitted or 1881@code{nil}, the function uses @code{0} as the base mode bits. The 1882complete and relative specifications can be combined, as in 1883@code{"u+r,g+rx,o+r,g-w"}. @xref{File permissions,,, coreutils, The 1884@sc{gnu} @code{Coreutils} Manual}, for a description of file mode 1885specifications. 1886@end defun 1887 1888@defun file-modes-symbolic-to-number modes &optional base-modes 1889This function converts a symbolic file mode specification in 1890@var{modes} into the equivalent integer. If the symbolic 1891specification is based on an existing file, that file's mode bits are 1892taken from the optional argument @var{base-modes}; if that argument is 1893omitted or @code{nil}, it defaults to 0, i.e., no access rights at 1894all. 1895@end defun 1896 1897@defun set-file-times filename &optional time 1898This function sets the access and modification times of @var{filename} 1899to @var{time}. The return value is @code{t} if the times are successfully 1900set, otherwise it is @code{nil}. @var{time} defaults to the current 1901time and must be a time value (@pxref{Time of Day}). 1902@end defun 1903 1904@defun set-file-extended-attributes filename attribute-alist 1905This function sets the Emacs-recognized extended file attributes for 1906@code{filename}. The second argument @var{attribute-alist} should be 1907an alist of the same form returned by @code{file-extended-attributes}. 1908The return value is @code{t} if the attributes are successfully set, 1909otherwise it is @code{nil}. 1910@xref{Extended Attributes}. 1911@end defun 1912 1913@defun set-file-selinux-context filename context 1914This function sets the SELinux security context for @var{filename} to 1915@var{context}. The @var{context} argument should be a list 1916@code{(@var{user} @var{role} @var{type} @var{range})}, where each 1917element is a string. @xref{Extended Attributes}. 1918 1919The function returns @code{t} if it succeeds in setting the SELinux 1920context of @var{filename}. It returns @code{nil} if the context was 1921not set (e.g., if SELinux is disabled, or if Emacs was compiled 1922without SELinux support). 1923@end defun 1924 1925@defun set-file-acl filename acl 1926This function sets the Access Control List for @var{filename} to 1927@var{acl}. The @var{acl} argument should have the same form returned 1928by the function @code{file-acl}. @xref{Extended Attributes}. 1929 1930The function returns @code{t} if it successfully sets the ACL of 1931@var{filename}, @code{nil} otherwise. 1932@end defun 1933 1934@node Files and Storage 1935@section Files and Secondary Storage 1936@cindex secondary storage 1937 1938After Emacs changes a file, there are two reasons the changes might 1939not survive later failures of power or media, both having to do with 1940efficiency. First, the operating system might alias written data with 1941data already stored elsewhere on secondary storage until one file or 1942the other is later modified; this will lose both files if the only 1943copy on secondary storage is lost due to media failure. Second, the 1944operating system might not write data to secondary storage 1945immediately, which will lose the data if power is lost. 1946 1947@findex write-region 1948Although both sorts of failures can largely be avoided by a suitably 1949configured file system, such systems are typically more expensive or 1950less efficient. In more-typical systems, to survive media failure you 1951can copy the file to a different device, and to survive a power 1952failure you can use the @code{write-region} function with the 1953@code{write-region-inhibit-fsync} variable set to @code{nil}. 1954@xref{Writing to Files}. 1955 1956@node File Names 1957@section File Names 1958@cindex file names 1959 1960 Files are generally referred to by their names, in Emacs as elsewhere. 1961File names in Emacs are represented as strings. The functions that 1962operate on a file all expect a file name argument. 1963 1964 In addition to operating on files themselves, Emacs Lisp programs 1965often need to operate on file names; i.e., to take them apart and to use 1966part of a name to construct related file names. This section describes 1967how to manipulate file names. 1968 1969 The functions in this section do not actually access files, so they 1970can operate on file names that do not refer to an existing file or 1971directory. 1972 1973@findex cygwin-convert-file-name-from-windows 1974@findex cygwin-convert-file-name-to-windows 1975@cindex MS-Windows file-name syntax 1976@cindex converting file names from/to MS-Windows syntax 1977 On MS-DOS and MS-Windows, these functions (like the function that 1978actually operate on files) accept MS-DOS or MS-Windows file-name syntax, 1979where backslashes separate the components, as well as POSIX syntax; but 1980they always return POSIX syntax. This enables Lisp programs to specify 1981file names in POSIX syntax and work properly on all systems without 1982change.@footnote{In MS-Windows versions of Emacs compiled for the Cygwin 1983environment, you can use the functions 1984@code{cygwin-convert-file-name-to-windows} and 1985@code{cygwin-convert-file-name-from-windows} to convert between the 1986two file-name syntaxes.} 1987 1988@menu 1989* File Name Components:: The directory part of a file name, and the rest. 1990* Relative File Names:: Some file names are relative to a current directory. 1991* Directory Names:: A directory's name as a directory 1992 is different from its name as a file. 1993* File Name Expansion:: Converting relative file names to absolute ones. 1994* Unique File Names:: Generating names for temporary files. 1995* File Name Completion:: Finding the completions for a given file name. 1996* Standard File Names:: If your package uses a fixed file name, 1997 how to handle various operating systems simply. 1998@end menu 1999 2000@node File Name Components 2001@subsection File Name Components 2002@cindex directory part (of file name) 2003@cindex nondirectory part (of file name) 2004@cindex version number (in file name) 2005 2006 The operating system groups files into directories. To specify a 2007file, you must specify the directory and the file's name within that 2008directory. Therefore, Emacs considers a file name as having two main 2009parts: the @dfn{directory name} part, and the @dfn{nondirectory} part 2010(or @dfn{file name within the directory}). Either part may be empty. 2011Concatenating these two parts reproduces the original file name. 2012 2013 On most systems, the directory part is everything up to and including 2014the last slash (backslash is also allowed in input on MS-DOS or 2015MS-Windows); the nondirectory part is the rest. 2016 2017 For some purposes, the nondirectory part is further subdivided into 2018the name proper and the @dfn{version number}. On most systems, only 2019backup files have version numbers in their names. 2020 2021@defun file-name-directory filename 2022This function returns the directory part of @var{filename}, as a 2023directory name (@pxref{Directory Names}), or @code{nil} if 2024@var{filename} does not include a directory part. 2025 2026On GNU and other POSIX-like systems, a string returned by this function always 2027ends in a slash. On MS-DOS it can also end in a colon. 2028 2029@example 2030@group 2031(file-name-directory "lewis/foo") ; @r{GNU example} 2032 @result{} "lewis/" 2033@end group 2034@group 2035(file-name-directory "foo") ; @r{GNU example} 2036 @result{} nil 2037@end group 2038@end example 2039@end defun 2040 2041@defun file-name-nondirectory filename 2042This function returns the nondirectory part of @var{filename}. 2043 2044@example 2045@group 2046(file-name-nondirectory "lewis/foo") 2047 @result{} "foo" 2048@end group 2049@group 2050(file-name-nondirectory "foo") 2051 @result{} "foo" 2052@end group 2053@group 2054(file-name-nondirectory "lewis/") 2055 @result{} "" 2056@end group 2057@end example 2058@end defun 2059 2060@defun file-name-sans-versions filename &optional keep-backup-version 2061This function returns @var{filename} with any file version numbers, 2062backup version numbers, or trailing tildes discarded. 2063 2064If @var{keep-backup-version} is non-@code{nil}, then true file version 2065numbers understood as such by the file system are discarded from the 2066return value, but backup version numbers are kept. 2067 2068@example 2069@group 2070(file-name-sans-versions "~rms/foo.~1~") 2071 @result{} "~rms/foo" 2072@end group 2073@group 2074(file-name-sans-versions "~rms/foo~") 2075 @result{} "~rms/foo" 2076@end group 2077@group 2078(file-name-sans-versions "~rms/foo") 2079 @result{} "~rms/foo" 2080@end group 2081@end example 2082@end defun 2083 2084@defun file-name-extension filename &optional period 2085This function returns @var{filename}'s final extension, if any, 2086after applying @code{file-name-sans-versions} to remove any 2087version/backup part. The extension, in a file name, is the part that 2088follows the last @samp{.} in the last name component (minus any 2089version/backup part). 2090 2091This function returns @code{nil} for extensionless file names such as 2092@file{foo}. It returns @code{""} for null extensions, as in 2093@file{foo.}. If the last component of a file name begins with a 2094@samp{.}, that @samp{.} doesn't count as the beginning of an 2095extension. Thus, @file{.emacs}'s extension is @code{nil}, not 2096@samp{.emacs}. 2097 2098If @var{period} is non-@code{nil}, then the returned value includes 2099the period that delimits the extension, and if @var{filename} has no 2100extension, the value is @code{""}. 2101@end defun 2102 2103@defun file-name-sans-extension filename 2104This function returns @var{filename} minus its extension, if any. The 2105version/backup part, if present, is only removed if the file has an 2106extension. For example, 2107 2108@example 2109(file-name-sans-extension "foo.lose.c") 2110 @result{} "foo.lose" 2111(file-name-sans-extension "big.hack/foo") 2112 @result{} "big.hack/foo" 2113(file-name-sans-extension "/my/home/.emacs") 2114 @result{} "/my/home/.emacs" 2115(file-name-sans-extension "/my/home/.emacs.el") 2116 @result{} "/my/home/.emacs" 2117(file-name-sans-extension "~/foo.el.~3~") 2118 @result{} "~/foo" 2119(file-name-sans-extension "~/foo.~3~") 2120 @result{} "~/foo.~3~" 2121@end example 2122 2123Note that the @samp{.~3~} in the two last examples is the backup part, 2124not an extension. 2125@end defun 2126 2127@defun file-name-base filename 2128This function is the composition of @code{file-name-sans-extension} 2129and @code{file-name-nondirectory}. For example, 2130 2131@example 2132(file-name-base "/my/home/foo.c") 2133 @result{} "foo" 2134@end example 2135@end defun 2136 2137@node Relative File Names 2138@subsection Absolute and Relative File Names 2139@cindex absolute file name 2140@cindex relative file name 2141 2142 All the directories in the file system form a tree starting at the 2143root directory. A file name can specify all the directory names 2144starting from the root of the tree; then it is called an 2145@dfn{absolute} file name. Or it can specify the position of the file 2146in the tree relative to a default directory; then it is called a 2147@dfn{relative} file name. On GNU and other POSIX-like systems, 2148after any leading @samp{~} has been expanded, an absolute file name 2149starts with a @samp{/} 2150(@pxref{abbreviate-file-name}), and a relative one does not. On 2151MS-DOS and MS-Windows, an absolute file name starts with a slash or a 2152backslash, or with a drive specification @samp{@var{x}:/}, where 2153@var{x} is the @dfn{drive letter}. 2154 2155@defun file-name-absolute-p filename 2156This function returns @code{t} if file @var{filename} is an absolute 2157file name, @code{nil} otherwise. A file name is considered to be 2158absolute if its first component is @samp{~}, or is @samp{~@var{user}} 2159where @var{user} is a valid login name. In the following examples, 2160assume that there is a user named @samp{rms} but no user named 2161@samp{nosuchuser}. 2162 2163@example 2164@group 2165(file-name-absolute-p "~rms/foo") 2166 @result{} t 2167@end group 2168@group 2169(file-name-absolute-p "~nosuchuser/foo") 2170 @result{} nil 2171@end group 2172@group 2173(file-name-absolute-p "rms/foo") 2174 @result{} nil 2175@end group 2176@group 2177(file-name-absolute-p "/user/rms/foo") 2178 @result{} t 2179@end group 2180@end example 2181@end defun 2182 2183 Given a possibly relative file name, you can expand any 2184leading @samp{~} and convert the result to an 2185absolute name using @code{expand-file-name} (@pxref{File Name 2186Expansion}). This function converts absolute file names to relative 2187names: 2188 2189@defun file-relative-name filename &optional directory 2190This function tries to return a relative name that is equivalent to 2191@var{filename}, assuming the result will be interpreted relative to 2192@var{directory} (an absolute directory name or directory file name). 2193If @var{directory} is omitted or @code{nil}, it defaults to the 2194current buffer's default directory. 2195 2196On some operating systems, an absolute file name begins with a device 2197name. On such systems, @var{filename} has no relative equivalent based 2198on @var{directory} if they start with two different device names. In 2199this case, @code{file-relative-name} returns @var{filename} in absolute 2200form. 2201 2202@example 2203(file-relative-name "/foo/bar" "/foo/") 2204 @result{} "bar" 2205(file-relative-name "/foo/bar" "/hack/") 2206 @result{} "../foo/bar" 2207@end example 2208@end defun 2209 2210@node Directory Names 2211@subsection Directory Names 2212@cindex directory name 2213@cindex directory file name 2214@cindex file name of directory 2215 2216 A @dfn{directory name} is a string that must name a directory if it 2217names any file at all. A directory is actually a kind of file, and it 2218has a file name (called the @dfn{directory file name}, which is 2219related to the directory name but is typically not identical. (This 2220is not quite the same as the usual POSIX terminology.) These two 2221names for the same entity are related by a syntactic transformation. 2222On GNU and other POSIX-like systems, this is simple: to obtain a 2223directory name, append a @samp{/} to a directory file name that does 2224not already end in @samp{/}. On MS-DOS the relationship is more 2225complicated. 2226 2227 The difference between a directory name and a directory file name is 2228subtle but crucial. When an Emacs variable or function argument is 2229described as being a directory name, a directory file name is not 2230acceptable. When @code{file-name-directory} returns a string, that is 2231always a directory name. 2232 2233 The following two functions convert between directory names and 2234directory file names. They do nothing special with environment 2235variable substitutions such as @samp{$HOME}, and the constructs 2236@samp{~}, @samp{.} and @samp{..}. 2237 2238@defun file-name-as-directory filename 2239This function returns a string representing @var{filename} in a form 2240that the operating system will interpret as the name of a directory (a 2241directory name). On most systems, this means appending a slash to the 2242string (if it does not already end in one). 2243 2244@example 2245@group 2246(file-name-as-directory "~rms/lewis") 2247 @result{} "~rms/lewis/" 2248@end group 2249@end example 2250@end defun 2251 2252@defun directory-name-p filename 2253This function returns non-@code{nil} if @var{filename} ends with a 2254directory separator character. This is the forward slash @samp{/} on 2255GNU and other POSIX-like systems; MS-Windows and MS-DOS recognize both 2256the forward slash and the backslash @samp{\} as directory separators. 2257@end defun 2258 2259@defun directory-file-name dirname 2260This function returns a string representing @var{dirname} in a form 2261that the operating system will interpret as the name of a file (a 2262directory file name). On most systems, this means removing the final 2263directory separators from the string, unless the string consists 2264entirely of directory separators. 2265 2266@example 2267@group 2268(directory-file-name "~lewis/") 2269 @result{} "~lewis" 2270@end group 2271@end example 2272@end defun 2273 2274 Given a directory name, you can combine it with a relative file name 2275using @code{concat}: 2276 2277@example 2278(concat @var{dirname} @var{relfile}) 2279@end example 2280 2281@noindent 2282Be sure to verify that the file name is relative before doing that. 2283If you use an absolute file name, the results could be syntactically 2284invalid or refer to the wrong file. 2285 2286 If you want to use a directory file name in making such a 2287combination, you must first convert it to a directory name using 2288@code{file-name-as-directory}: 2289 2290@example 2291(concat (file-name-as-directory @var{dirfile}) @var{relfile}) 2292@end example 2293 2294@noindent 2295Don't try concatenating a slash by hand, as in 2296 2297@example 2298;;; @r{Wrong!} 2299(concat @var{dirfile} "/" @var{relfile}) 2300@end example 2301 2302@noindent 2303because this is not portable. Always use 2304@code{file-name-as-directory}. 2305 2306 To avoid the issues mentioned above, or if the @var{dirname} value 2307might be @code{nil} (for example, from an element of @code{load-path}), 2308use: 2309 2310@example 2311(expand-file-name @var{relfile} @var{dirname}) 2312@end example 2313 2314However, @code{expand-file-name} expands leading @samp{~} in 2315@var{relfile}, which may not be what you want. @xref{File Name 2316Expansion}. 2317 2318 To convert a directory name to its abbreviation, use this 2319function: 2320 2321@cindex file name abbreviations 2322@cindex abbreviated file names 2323@vindex directory-abbrev-alist 2324@defun abbreviate-file-name filename 2325@anchor{abbreviate-file-name} 2326This function returns an abbreviated form of @var{filename}. It 2327applies the abbreviations specified in @code{directory-abbrev-alist} 2328(@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}), 2329then substitutes @samp{~} for the user's home directory if the 2330argument names a file in the home directory or one of its 2331subdirectories. If the home directory is a root directory, it is not 2332replaced with @samp{~}, because this does not make the result shorter 2333on many systems. 2334 2335You can use this function for directory names and for file names, 2336because it recognizes abbreviations even as part of the name. 2337@end defun 2338 2339@node File Name Expansion 2340@subsection Functions that Expand Filenames 2341@cindex expansion of file names 2342 2343 @dfn{Expanding} a file name means converting a relative file name to 2344an absolute one. Since this is done relative to a default directory, 2345you must specify the default directory as well as the file name 2346to be expanded. It also involves expanding abbreviations like 2347@file{~/} 2348@ifnottex 2349(@pxref{abbreviate-file-name}), 2350@end ifnottex 2351and eliminating redundancies like @file{./} and @file{@var{name}/../}. 2352 2353@defun expand-file-name filename &optional directory 2354This function converts @var{filename} to an absolute file name. If 2355@var{directory} is supplied, it is the default directory to start with 2356if @var{filename} is relative and does not start with @samp{~}. 2357(The value of @var{directory} should 2358itself be an absolute directory name or directory file name; it may 2359start with @samp{~}.) Otherwise, the current buffer's value of 2360@code{default-directory} is used. For example: 2361 2362@example 2363@group 2364(expand-file-name "foo") 2365 @result{} "/xcssun/users/rms/lewis/foo" 2366@end group 2367@group 2368(expand-file-name "../foo") 2369 @result{} "/xcssun/users/rms/foo" 2370@end group 2371@group 2372(expand-file-name "foo" "/usr/spool/") 2373 @result{} "/usr/spool/foo" 2374@end group 2375@end example 2376 2377If the part of @var{filename} before the first slash is 2378@samp{~}, it expands to your home directory, which is typically 2379specified by the value of the @env{HOME} environment variable 2380(@pxref{General Variables,,, emacs, The GNU Emacs Manual}). 2381If the part before the first 2382slash is @samp{~@var{user}} and if @var{user} is a valid login name, 2383it expands to @var{user}'s home directory. 2384If you do not want this expansion for a relative @var{filename} that 2385might begin with a literal @samp{~}, you can use @code{(concat 2386(file-name-as-directory directory) filename)} instead of 2387@code{(expand-file-name filename directory)}. 2388 2389Filenames containing @samp{.} or @samp{..} are simplified to their 2390canonical form: 2391 2392@example 2393@group 2394(expand-file-name "bar/../foo") 2395 @result{} "/xcssun/users/rms/lewis/foo" 2396@end group 2397@end example 2398 2399In some cases, a leading @samp{..} component can remain in the output: 2400 2401@example 2402@group 2403(expand-file-name "../home" "/") 2404 @result{} "/../home" 2405@end group 2406@end example 2407 2408@noindent 2409This is for the sake of filesystems that have the concept of a 2410superroot above the root directory @file{/}. On other filesystems, 2411@file{/../} is interpreted exactly the same as @file{/}. 2412 2413Expanding @file{.} or the empty string returns the default directory: 2414 2415@example 2416@group 2417(expand-file-name "." "/usr/spool/") 2418 @result{} "/usr/spool" 2419(expand-file-name "" "/usr/spool/") 2420 @result{} "/usr/spool" 2421@end group 2422@end example 2423 2424Note that @code{expand-file-name} does @emph{not} expand environment 2425variables; only @code{substitute-in-file-name} does that: 2426 2427@example 2428@group 2429(expand-file-name "$HOME/foo") 2430 @result{} "/xcssun/users/rms/lewis/$HOME/foo" 2431@end group 2432@end example 2433 2434Note also that @code{expand-file-name} does not follow symbolic links 2435at any level. This results in a difference between the way 2436@code{file-truename} and @code{expand-file-name} treat @samp{..}. 2437Assuming that @samp{/tmp/bar} is a symbolic link to the directory 2438@samp{/tmp/foo/bar} we get: 2439 2440@example 2441@group 2442(file-truename "/tmp/bar/../myfile") 2443 @result{} "/tmp/foo/myfile" 2444@end group 2445@group 2446(expand-file-name "/tmp/bar/../myfile") 2447 @result{} "/tmp/myfile" 2448@end group 2449@end example 2450 2451If you may need to follow symbolic links preceding @samp{..}, you 2452should make sure to call @code{file-truename} without prior direct or 2453indirect calls to @code{expand-file-name}. @xref{Truenames}. 2454@end defun 2455 2456@defvar default-directory 2457The value of this buffer-local variable is the default directory for the 2458current buffer. It should be an absolute directory name; it may start 2459with @samp{~}. This variable is buffer-local in every buffer. 2460 2461@code{expand-file-name} uses the default directory when its second 2462argument is @code{nil}. 2463 2464The value is always a string ending with a slash. 2465 2466@example 2467@group 2468default-directory 2469 @result{} "/user/lewis/manual/" 2470@end group 2471@end example 2472@end defvar 2473 2474@defun substitute-in-file-name filename 2475@anchor{Definition of substitute-in-file-name} 2476This function replaces environment variable references in 2477@var{filename} with the environment variable values. Following 2478standard Unix shell syntax, @samp{$} is the prefix to substitute an 2479environment variable value. If the input contains @samp{$$}, that is 2480converted to @samp{$}; this gives the user a way to quote a 2481@samp{$}. 2482 2483The environment variable name is the series of alphanumeric characters 2484(including underscores) that follow the @samp{$}. If the character following 2485the @samp{$} is a @samp{@{}, then the variable name is everything up to the 2486matching @samp{@}}. 2487 2488Calling @code{substitute-in-file-name} on output produced by 2489@code{substitute-in-file-name} tends to give incorrect results. For 2490instance, use of @samp{$$} to quote a single @samp{$} won't work 2491properly, and @samp{$} in an environment variable's value could lead 2492to repeated substitution. Therefore, programs that call this function 2493and put the output where it will be passed to this function need to 2494double all @samp{$} characters to prevent subsequent incorrect 2495results. 2496 2497@c Wordy to avoid overfull hbox. --rjc 15mar92 2498Here we assume that the environment variable @env{HOME}, which holds 2499the user's home directory, has value @samp{/xcssun/users/rms}. 2500 2501@example 2502@group 2503(substitute-in-file-name "$HOME/foo") 2504 @result{} "/xcssun/users/rms/foo" 2505@end group 2506@end example 2507 2508After substitution, if a @samp{~} or a @samp{/} appears immediately 2509after another @samp{/}, the function discards everything before it (up 2510through the immediately preceding @samp{/}). 2511 2512@example 2513@group 2514(substitute-in-file-name "bar/~/foo") 2515 @result{} "~/foo" 2516@end group 2517@group 2518(substitute-in-file-name "/usr/local/$HOME/foo") 2519 @result{} "/xcssun/users/rms/foo" 2520 ;; @r{@file{/usr/local/} has been discarded.} 2521@end group 2522@end example 2523 2524@end defun 2525 2526 Sometimes, it is not desired to expand file names. In such cases, 2527the file name can be quoted to suppress the expansion, and to handle 2528the file name literally. Quoting happens by prefixing the file name 2529with @samp{/:}. 2530 2531@defmac file-name-quote name 2532This macro adds the quotation prefix @samp{/:} to the file @var{name}. 2533For a local file @var{name}, it prefixes @var{name} with @samp{/:}. 2534If @var{name} is a remote file name, the local part of @var{name} 2535(@pxref{Magic File Names}) is quoted. If @var{name} is already a 2536quoted file name, @var{name} is returned unchanged. 2537 2538@example 2539@group 2540(substitute-in-file-name (file-name-quote "bar/~/foo")) 2541 @result{} "/:bar/~/foo" 2542@end group 2543 2544@group 2545(substitute-in-file-name (file-name-quote "/ssh:host:bar/~/foo")) 2546 @result{} "/ssh:host:/:bar/~/foo" 2547@end group 2548@end example 2549 2550The macro cannot be used to suppress file name handlers from magic 2551file names (@pxref{Magic File Names}). 2552@end defmac 2553 2554@defmac file-name-unquote name 2555This macro removes the quotation prefix @samp{/:} from the file 2556@var{name}, if any. If @var{name} is a remote file name, the local 2557part of @var{name} is unquoted. 2558@end defmac 2559 2560@defmac file-name-quoted-p name 2561This macro returns non-@code{nil}, when @var{name} is quoted with the 2562prefix @samp{/:}. If @var{name} is a remote file name, the local part 2563of @var{name} is checked. 2564@end defmac 2565 2566 2567@node Unique File Names 2568@subsection Generating Unique File Names 2569@cindex unique file names 2570@cindex temporary files 2571 2572 Some programs need to write temporary files. Here is the usual way to 2573construct a name for such a file: 2574 2575@example 2576(make-temp-file @var{name-of-application}) 2577@end example 2578 2579@noindent 2580The job of @code{make-temp-file} is to prevent two different users or 2581two different jobs from trying to use the exact same file name. 2582 2583@defun make-temp-file prefix &optional dir-flag suffix text 2584This function creates a temporary file and returns its name. Emacs 2585creates the temporary file's name by adding to @var{prefix} some 2586random characters that are different in each Emacs job. The result is 2587guaranteed to be a newly created file, containing @var{text} if that's 2588given as a string and empty otherwise. On MS-DOS, this function can 2589truncate @var{prefix} to fit into the 8+3 file-name limits. If 2590@var{prefix} is a relative file name, it is expanded against 2591@code{temporary-file-directory}. 2592 2593@example 2594@group 2595(make-temp-file "foo") 2596 @result{} "/tmp/foo232J6v" 2597@end group 2598@end example 2599 2600When @code{make-temp-file} returns, the file has been created and is 2601empty. At that point, you should write the intended contents into the 2602file. 2603 2604If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an 2605empty directory instead of an empty file. It returns the file name, 2606not the directory name, of that directory. @xref{Directory Names}. 2607 2608If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at 2609the end of the file name. 2610 2611If @var{text} is a string, @code{make-temp-file} inserts it in the file. 2612 2613To prevent conflicts among different libraries running in the same 2614Emacs, each Lisp program that uses @code{make-temp-file} should have its 2615own @var{prefix}. The number added to the end of @var{prefix} 2616distinguishes between the same application running in different Emacs 2617jobs. Additional added characters permit a large number of distinct 2618names even in one Emacs job. 2619@end defun 2620 2621 The default directory for temporary files is controlled by the 2622variable @code{temporary-file-directory}. This variable gives the user 2623a uniform way to specify the directory for all temporary files. Some 2624programs use @code{small-temporary-file-directory} instead, if that is 2625non-@code{nil}. To use it, you should expand the prefix against 2626the proper directory before calling @code{make-temp-file}. 2627 2628@defopt temporary-file-directory 2629@cindex @env{TMPDIR} environment variable 2630@cindex @env{TMP} environment variable 2631@cindex @env{TEMP} environment variable 2632This variable specifies the directory name for creating temporary files. 2633Its value should be a directory name (@pxref{Directory Names}), but it 2634is good for Lisp programs to cope if the value is a directory's file 2635name instead. Using the value as the second argument to 2636@code{expand-file-name} is a good way to achieve that. 2637 2638The default value is determined in a reasonable way for your operating 2639system; it is based on the @env{TMPDIR}, @env{TMP} and @env{TEMP} 2640environment variables, with a fall-back to a system-dependent name if 2641none of these variables is defined. 2642 2643Even if you do not use @code{make-temp-file} to create the temporary 2644file, you should still use this variable to decide which directory to 2645put the file in. However, if you expect the file to be small, you 2646should use @code{small-temporary-file-directory} first if that is 2647non-@code{nil}. 2648@end defopt 2649 2650@defopt small-temporary-file-directory 2651This variable specifies the directory name for 2652creating certain temporary files, which are likely to be small. 2653 2654If you want to write a temporary file which is likely to be small, you 2655should compute the directory like this: 2656 2657@example 2658(make-temp-file 2659 (expand-file-name @var{prefix} 2660 (or small-temporary-file-directory 2661 temporary-file-directory))) 2662@end example 2663@end defopt 2664 2665@defun make-temp-name base-name 2666This function generates a string that might be a unique file 2667name. The name starts with @var{base-name}, and has several random 2668characters appended to it, which are different in each Emacs job. It 2669is like @code{make-temp-file} except that (i) it just constructs a 2670name and does not create a file, (ii) @var{base-name} should be an 2671absolute file name that is not magic, and (iii) if the returned file 2672name is magic, it might name an existing file. @xref{Magic File 2673Names}. 2674 2675@strong{Warning:} In most cases, you should not use this function; use 2676@code{make-temp-file} instead! This function is susceptible to a race 2677condition, between the @code{make-temp-name} call and the creation of 2678the file, which in some cases may cause a security hole. 2679@end defun 2680 2681Sometimes, it is necessary to create a temporary file on a remote host 2682or a mounted directory. The following two functions support this. 2683 2684@cindex temporary file on a remote host 2685@defun make-nearby-temp-file prefix &optional dir-flag suffix 2686This function is similar to @code{make-temp-file}, but it creates a 2687temporary file as close as possible to @code{default-directory}. If 2688@var{prefix} is a relative file name, and @code{default-directory} is 2689a remote file name or located on a mounted file systems, the temporary 2690file is created in the directory returned by the function 2691@code{temporary-file-directory}. Otherwise, the function 2692@code{make-temp-file} is used. @var{prefix}, @var{dir-flag} and 2693@var{suffix} have the same meaning as in @code{make-temp-file}. 2694 2695@example 2696@group 2697(let ((default-directory "/ssh:remotehost:")) 2698 (make-nearby-temp-file "foo")) 2699 @result{} "/ssh:remotehost:/tmp/foo232J6v" 2700@end group 2701@end example 2702@end defun 2703 2704@defun temporary-file-directory 2705The directory for writing temporary files via 2706@code{make-nearby-temp-file}. In case of a remote 2707@code{default-directory}, this is a directory for temporary files on 2708that remote host. If such a directory does not exist, or 2709@code{default-directory} ought to be located on a mounted file system 2710(see @code{mounted-file-systems}), the function returns 2711@code{default-directory}. For a non-remote and non-mounted 2712@code{default-directory}, the value of the variable 2713@code{temporary-file-directory} is returned. 2714@end defun 2715 2716In order to extract the local part of the file's name of a temporary 2717file, use @code{file-local-name} (@pxref{Magic File Names}). 2718 2719@node File Name Completion 2720@subsection File Name Completion 2721@cindex file name completion subroutines 2722@cindex completion, file name 2723 2724 This section describes low-level subroutines for completing a file 2725name. For higher level functions, see @ref{Reading File Names}. 2726 2727@defun file-name-all-completions partial-filename directory 2728This function returns a list of all possible completions for a file 2729whose name starts with @var{partial-filename} in directory 2730@var{directory}. The order of the completions is the order of the files 2731in the directory, which is unpredictable and conveys no useful 2732information. 2733 2734The argument @var{partial-filename} must be a file name containing no 2735directory part and no slash (or backslash on some systems). The current 2736buffer's default directory is prepended to @var{directory}, if 2737@var{directory} is not absolute. 2738 2739In the following example, suppose that @file{~rms/lewis} is the current 2740default directory, and has five files whose names begin with @samp{f}: 2741@file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and 2742@file{file.c.~2~}. 2743 2744@example 2745@group 2746(file-name-all-completions "f" "") 2747 @result{} ("foo" "file~" "file.c.~2~" 2748 "file.c.~1~" "file.c") 2749@end group 2750 2751@group 2752(file-name-all-completions "fo" "") 2753 @result{} ("foo") 2754@end group 2755@end example 2756@end defun 2757 2758@defun file-name-completion filename directory &optional predicate 2759This function completes the file name @var{filename} in directory 2760@var{directory}. It returns the longest prefix common to all file names 2761in directory @var{directory} that start with @var{filename}. If 2762@var{predicate} is non-@code{nil} then it ignores possible completions 2763that don't satisfy @var{predicate}, after calling that function 2764with one argument, the expanded absolute file name. 2765 2766If only one match exists and @var{filename} matches it exactly, the 2767function returns @code{t}. The function returns @code{nil} if directory 2768@var{directory} contains no name starting with @var{filename}. 2769 2770In the following example, suppose that the current default directory 2771has five files whose names begin with @samp{f}: @file{foo}, 2772@file{file~}, @file{file.c}, @file{file.c.~1~}, and 2773@file{file.c.~2~}. 2774 2775@example 2776@group 2777(file-name-completion "fi" "") 2778 @result{} "file" 2779@end group 2780 2781@group 2782(file-name-completion "file.c.~1" "") 2783 @result{} "file.c.~1~" 2784@end group 2785 2786@group 2787(file-name-completion "file.c.~1~" "") 2788 @result{} t 2789@end group 2790 2791@group 2792(file-name-completion "file.c.~3" "") 2793 @result{} nil 2794@end group 2795@end example 2796@end defun 2797 2798@defopt completion-ignored-extensions 2799@code{file-name-completion} usually ignores file names that end in any 2800string in this list. It does not ignore them when all the possible 2801completions end in one of these suffixes. This variable has no effect 2802on @code{file-name-all-completions}. 2803 2804A typical value might look like this: 2805 2806@example 2807@group 2808completion-ignored-extensions 2809 @result{} (".o" ".elc" "~" ".dvi") 2810@end group 2811@end example 2812 2813If an element of @code{completion-ignored-extensions} ends in a slash 2814@samp{/}, it signals a directory. The elements which do @emph{not} end 2815in a slash will never match a directory; thus, the above value will not 2816filter out a directory named @file{foo.elc}. 2817@end defopt 2818 2819@node Standard File Names 2820@subsection Standard File Names 2821 2822 Sometimes, an Emacs Lisp program needs to specify a standard file 2823name for a particular use---typically, to hold configuration data 2824specified by the current user. Usually, such files should be located 2825in the directory specified by @code{user-emacs-directory}, which is 2826typically @file{~/.config/emacs/} or @file{~/.emacs.d/} by default (@pxref{Find 2827Init,,How Emacs Finds Your Init File, emacs, The GNU Emacs Manual}). 2828For example, abbrev definitions are stored by default in 2829@file{~/.config/emacs/abbrev_defs} or @file{~/.emacs.d/abbrev_defs}. 2830The easiest way to specify such a file name is to use the function 2831@code{locate-user-emacs-file}. 2832 2833@defun locate-user-emacs-file base-name &optional old-name 2834This function returns an absolute file name for an Emacs-specific 2835configuration or data file. The argument @file{base-name} should be a 2836relative file name. The return value is the absolute name of a file 2837in the directory specified by @code{user-emacs-directory}; if that 2838directory does not exist, this function creates it. 2839 2840If the optional argument @var{old-name} is non-@code{nil}, it 2841specifies a file in the user's home directory, 2842@file{~/@var{old-name}}. If such a file exists, the return value is 2843the absolute name of that file, instead of the file specified by 2844@var{base-name}. This argument is intended to be used by Emacs 2845packages to provide backward compatibility. For instance, prior to 2846the introduction of @code{user-emacs-directory}, the abbrev file was 2847located in @file{~/.abbrev_defs}. Here is the definition of 2848@code{abbrev-file-name}: 2849 2850@example 2851(defcustom abbrev-file-name 2852 (locate-user-emacs-file "abbrev_defs" ".abbrev_defs") 2853 "Default name of file from which to read abbrevs." 2854 @dots{} 2855 :type 'file) 2856@end example 2857@end defun 2858 2859 A lower-level function for standardizing file names, which 2860@code{locate-user-emacs-file} uses as a subroutine, is 2861@code{convert-standard-filename}. 2862 2863@defun convert-standard-filename filename 2864This function returns a file name based on @var{filename}, which fits 2865the conventions of the current operating system. 2866 2867On GNU and other POSIX-like systems, this simply returns @var{filename}. 2868On other operating systems, it may enforce system-specific file name 2869conventions; for example, on MS-DOS this function performs a variety 2870of changes to enforce MS-DOS file name limitations, including 2871converting any leading @samp{.} to @samp{_} and truncating to three 2872characters after the @samp{.}. 2873 2874The recommended way to use this function is to specify a name which 2875fits the conventions of GNU and Unix systems, and pass it to 2876@code{convert-standard-filename}. 2877@end defun 2878 2879@node Contents of Directories 2880@section Contents of Directories 2881@cindex directory-oriented functions 2882@cindex file names in directory 2883 2884 A directory is a kind of file that contains other files entered under 2885various names. Directories are a feature of the file system. 2886 2887 Emacs can list the names of the files in a directory as a Lisp list, 2888or display the names in a buffer using the @code{ls} shell command. In 2889the latter case, it can optionally display information about each file, 2890depending on the options passed to the @code{ls} command. 2891 2892@defun directory-files directory &optional full-name match-regexp nosort 2893This function returns a list of the names of the files in the directory 2894@var{directory}. By default, the list is in alphabetical order. 2895 2896If @var{full-name} is non-@code{nil}, the function returns the files' 2897absolute file names. Otherwise, it returns the names relative to 2898the specified directory. 2899 2900If @var{match-regexp} is non-@code{nil}, this function returns only 2901those file names that contain a match for that regular expression---the 2902other file names are excluded from the list. On case-insensitive 2903filesystems, the regular expression matching is case-insensitive. 2904 2905@c Emacs 19 feature 2906If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort 2907the list, so you get the file names in no particular order. Use this if 2908you want the utmost possible speed and don't care what order the files 2909are processed in. If the order of processing is visible to the user, 2910then the user will probably be happier if you do sort the names. 2911 2912@example 2913@group 2914(directory-files "~lewis") 2915 @result{} ("#foo#" "#foo.el#" "." ".." 2916 "dired-mods.el" "files.texi" 2917 "files.texi.~1~") 2918@end group 2919@end example 2920 2921An error is signaled if @var{directory} is not the name of a directory 2922that can be read. 2923@end defun 2924 2925@cindex recursive traverse of directory tree 2926@defun directory-files-recursively directory regexp &optional include-directories predicate follow-symlinks 2927Return all files under @var{directory} whose names match @var{regexp}. 2928This function searches the specified @var{directory} and its 2929sub-directories, recursively, for files whose basenames (i.e., without 2930the leading directories) match the specified @var{regexp}, and returns 2931a list of the absolute file names of the matching files 2932(@pxref{Relative File Names, absolute file names}). The file names 2933are returned in depth-first order, meaning that files in some 2934sub-directory are returned before the files in its parent directory. 2935In addition, matching files found in each subdirectory are sorted 2936alphabetically by their basenames. By default, directories whose 2937names match @var{regexp} are omitted from the list, but if the 2938optional argument @var{include-directories} is non-@code{nil}, they 2939are included. 2940 2941By default, all subdirectories are descended into. If @var{predicate} 2942is @code{t}, errors when trying to descend into a subdirectory (for 2943instance, if it's not readable by this user) are ignored. If it's 2944neither @code{nil} nor @code{t}, it should be a function that takes 2945one parameter (the subdirectory name) and should return non-@code{nil} 2946if the directory is to be descended into. 2947 2948Symbolic links to subdirectories are not followed by default, but if 2949@var{follow-symlinks} is non-@code{nil}, they are followed. 2950@end defun 2951 2952 2953@defun locate-dominating-file file name 2954Starting at @var{file}, go up the directory tree hierarchy looking for 2955the first directory where @var{name}, a string, exists, and return that 2956directory. If @var{file} is a file, its directory will serve as the 2957starting point for the search; otherwise @var{file} should be a 2958directory from which to start. The function looks in the starting 2959directory, then in its parent, then in its parent's parent, etc., 2960until it either finds a directory with @var{name} or reaches the root 2961directory of the filesystem without finding @var{name} -- in the 2962latter case the function returns @code{nil}. 2963 2964The argument @code{name} can also be a predicate function. The 2965predicate is called for every directory examined by the function, 2966starting from @var{file} (even if @var{file} is not a directory). It 2967is called with one argument (the file or directory) and should return 2968non-@code{nil} if that directory is the one it is looking for. 2969@end defun 2970 2971@defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format 2972This is similar to @code{directory-files} in deciding which files 2973to report on and how to report their names. However, instead 2974of returning a list of file names, it returns for each file a 2975list @code{(@var{filename} . @var{attributes})}, where @var{attributes} 2976is what @code{file-attributes} returns for that file. 2977The optional argument @var{id-format} has the same meaning as the 2978corresponding argument to @code{file-attributes} (@pxref{Definition 2979of file-attributes}). 2980@end defun 2981 2982@defun file-expand-wildcards pattern &optional full 2983This function expands the wildcard pattern @var{pattern}, returning 2984a list of file names that match it. 2985 2986If @var{pattern} is written as an absolute file name, 2987the values are absolute also. 2988 2989If @var{pattern} is written as a relative file name, it is interpreted 2990relative to the current default directory. The file names returned are 2991normally also relative to the current default directory. However, if 2992@var{full} is non-@code{nil}, they are absolute. 2993@end defun 2994 2995@defun insert-directory file switches &optional wildcard full-directory-p 2996This function inserts (in the current buffer) a directory listing for 2997directory @var{file}, formatted with @code{ls} according to 2998@var{switches}. It leaves point after the inserted text. 2999@var{switches} may be a string of options, or a list of strings 3000representing individual options. 3001 3002The argument @var{file} may be either a directory or a file 3003specification including wildcard characters. If @var{wildcard} is 3004non-@code{nil}, that means treat @var{file} as a file specification with 3005wildcards. 3006 3007If @var{full-directory-p} is non-@code{nil}, that means the directory 3008listing is expected to show the full contents of a directory. You 3009should specify @code{t} when @var{file} is a directory and switches do 3010not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to 3011describe a directory itself as a file, rather than showing its 3012contents.) 3013 3014On most systems, this function works by running a directory listing 3015program whose name is in the variable @code{insert-directory-program}. 3016If @var{wildcard} is non-@code{nil}, it also runs the shell specified by 3017@code{shell-file-name}, to expand the wildcards. 3018 3019MS-DOS and MS-Windows systems usually lack the standard Unix program 3020@code{ls}, so this function emulates the standard Unix program @code{ls} 3021with Lisp code. 3022 3023As a technical detail, when @var{switches} contains the long 3024@samp{--dired} option, @code{insert-directory} treats it specially, 3025for the sake of dired. However, the normally equivalent short 3026@samp{-D} option is just passed on to @code{insert-directory-program}, 3027as any other option. 3028@end defun 3029 3030@defvar insert-directory-program 3031This variable's value is the program to run to generate a directory listing 3032for the function @code{insert-directory}. It is ignored on systems 3033which generate the listing with Lisp code. 3034@end defvar 3035 3036@node Create/Delete Dirs 3037@section Creating, Copying and Deleting Directories 3038@cindex creating, copying and deleting directories 3039@c Emacs 19 features 3040 3041 Most Emacs Lisp file-manipulation functions get errors when used on 3042files that are directories. For example, you cannot delete a directory 3043with @code{delete-file}. These special functions exist to create and 3044delete directories. 3045 3046@findex mkdir 3047@deffn Command make-directory dirname &optional parents 3048This command creates a directory named @var{dirname}. If 3049@var{parents} is non-@code{nil}, as is always the case in an 3050interactive call, that means to create the parent directories first, 3051if they don't already exist. 3052@code{mkdir} is an alias for this. 3053@end deffn 3054 3055@deffn Command make-empty-file filename &optional parents 3056This command creates an empty file named @var{filename}. 3057As @code{make-directory}, this command creates parent directories 3058if @var{parents} is non-@code{nil}. 3059If @var{filename} already exists, this command signals an error. 3060@end deffn 3061 3062@deffn Command copy-directory dirname newname &optional keep-time parents copy-contents 3063This command copies the directory named @var{dirname} to 3064@var{newname}. If @var{newname} is a directory name, 3065@var{dirname} will be copied to a subdirectory there. 3066@xref{Directory Names}. 3067 3068It always sets the file modes of the copied files to match the 3069corresponding original file. 3070 3071The third argument @var{keep-time} non-@code{nil} means to preserve the 3072modification time of the copied files. A prefix arg makes 3073@var{keep-time} non-@code{nil}. 3074 3075The fourth argument @var{parents} says whether to 3076create parent directories if they don't exist. Interactively, 3077this happens by default. 3078 3079The fifth argument @var{copy-contents}, if non-@code{nil}, means to 3080copy the contents of @var{dirname} directly into @var{newname} if the 3081latter is a directory name, instead of copying @var{dirname} into 3082it as a subdirectory. 3083@end deffn 3084 3085@cindex trash 3086@vindex delete-by-moving-to-trash 3087@deffn Command delete-directory dirname &optional recursive trash 3088This command deletes the directory named @var{dirname}. The function 3089@code{delete-file} does not work for files that are directories; you 3090must use @code{delete-directory} for them. If @var{recursive} is 3091@code{nil}, and the directory contains any files, 3092@code{delete-directory} signals an error. 3093If recursive is non-@code{nil}, there is no error merely because the 3094directory or its files are deleted by some other process before 3095@code{delete-directory} gets to them. 3096 3097@code{delete-directory} only follows symbolic links at the level of 3098parent directories. 3099 3100If the optional argument @var{trash} is non-@code{nil} and the 3101variable @code{delete-by-moving-to-trash} is non-@code{nil}, this 3102command moves the file into the system Trash instead of deleting it. 3103@xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU 3104Emacs Manual}. When called interactively, @var{trash} is @code{t} if 3105no prefix argument is given, and @code{nil} otherwise. 3106@end deffn 3107 3108@node Magic File Names 3109@section Making Certain File Names ``Magic'' 3110@cindex magic file names 3111 3112 You can implement special handling for certain file names. This is 3113called making those names @dfn{magic}. The principal use for this 3114feature is in implementing access to remote files (@pxref{Remote Files,, 3115Remote Files, emacs, The GNU Emacs Manual}). 3116 3117 To define a kind of magic file name, you must supply a regular 3118expression to define the class of names (all those that match the 3119regular expression), plus a handler that implements all the primitive 3120Emacs file operations for file names that match. 3121 3122@cindex file name handler 3123@vindex file-name-handler-alist 3124 The variable @code{file-name-handler-alist} holds a list of handlers, 3125together with regular expressions that determine when to apply each 3126handler. Each element has this form: 3127 3128@example 3129(@var{regexp} . @var{handler}) 3130@end example 3131 3132@noindent 3133All the Emacs primitives for file access and file name transformation 3134check the given file name against @code{file-name-handler-alist}. If 3135the file name matches @var{regexp}, the primitives handle that file by 3136calling @var{handler}. 3137 3138 The first argument given to @var{handler} is the name of the 3139primitive, as a symbol; the remaining arguments are the arguments that 3140were passed to that primitive. (The first of these arguments is most 3141often the file name itself.) For example, if you do this: 3142 3143@example 3144(file-exists-p @var{filename}) 3145@end example 3146 3147@noindent 3148and @var{filename} has handler @var{handler}, then @var{handler} is 3149called like this: 3150 3151@example 3152(funcall @var{handler} 'file-exists-p @var{filename}) 3153@end example 3154 3155 When a function takes two or more arguments that must be file names, 3156it checks each of those names for a handler. For example, if you do 3157this: 3158 3159@example 3160(expand-file-name @var{filename} @var{dirname}) 3161@end example 3162 3163@noindent 3164then it checks for a handler for @var{filename} and then for a handler 3165for @var{dirname}. In either case, the @var{handler} is called like 3166this: 3167 3168@example 3169(funcall @var{handler} 'expand-file-name @var{filename} @var{dirname}) 3170@end example 3171 3172@noindent 3173The @var{handler} then needs to figure out whether to handle 3174@var{filename} or @var{dirname}. 3175 3176 If the specified file name matches more than one handler, the one 3177whose match starts last in the file name gets precedence. This rule 3178is chosen so that handlers for jobs such as uncompression are handled 3179first, before handlers for jobs such as remote file access. 3180 3181 Here are the operations that a magic file name handler gets to handle: 3182 3183@ifnottex 3184@noindent 3185@code{access-file}, @code{add-name-to-file}, 3186@code{byte-compiler-base-file-name},@* 3187@code{copy-directory}, @code{copy-file}, 3188@code{delete-directory}, @code{delete-file}, 3189@code{diff-latest-backup-file}, 3190@code{directory-file-name}, 3191@code{directory-files}, 3192@code{directory-files-and-attributes}, 3193@code{dired-compress-file}, @code{dired-uncache}, 3194@code{exec-path}, @code{expand-file-name},@* 3195@code{file-accessible-directory-p}, 3196@code{file-acl}, 3197@code{file-attributes}, 3198@code{file-directory-p}, 3199@code{file-equal-p}, 3200@code{file-executable-p}, @code{file-exists-p}, 3201@code{file-in-directory-p}, 3202@code{file-local-copy}, 3203@code{file-modes}, @code{file-name-all-completions}, 3204@code{file-name-as-directory}, 3205@code{file-name-case-insensitive-p}, 3206@code{file-name-completion}, 3207@code{file-name-directory}, 3208@code{file-name-nondirectory}, 3209@code{file-name-sans-versions}, @code{file-newer-than-file-p}, 3210@code{file-notify-add-watch}, @code{file-notify-rm-watch}, 3211@code{file-notify-valid-p}, 3212@code{file-ownership-preserved-p}, 3213@code{file-readable-p}, @code{file-regular-p}, 3214@code{file-remote-p}, @code{file-selinux-context}, 3215@code{file-symlink-p}, @code{file-system-info}, 3216@code{file-truename}, @code{file-writable-p}, 3217@code{find-backup-file-name},@* 3218@code{get-file-buffer}, 3219@code{insert-directory}, 3220@code{insert-file-contents},@* 3221@code{load}, 3222@code{make-auto-save-file-name}, 3223@code{make-directory}, 3224@code{make-directory-internal}, 3225@code{make-nearby-temp-file}, 3226@code{make-process}, 3227@code{make-symbolic-link},@* 3228@code{process-file}, 3229@code{rename-file}, @code{set-file-acl}, @code{set-file-modes}, 3230@code{set-file-selinux-context}, @code{set-file-times}, 3231@code{set-visited-file-modtime}, @code{shell-command}, 3232@code{start-file-process}, 3233@code{substitute-in-file-name},@* 3234@code{temporary-file-directory}, 3235@code{unhandled-file-name-directory}, 3236@code{vc-registered}, 3237@code{verify-visited-file-modtime},@* 3238@code{write-region}. 3239@end ifnottex 3240@iftex 3241@noindent 3242@flushleft 3243@code{access-file}, @code{add-name-to-file}, 3244@code{byte-com@discretionary{}{}{}piler-base-file-name}, 3245@code{copy-directory}, @code{copy-file}, 3246@code{delete-directory}, @code{delete-file}, 3247@code{diff-latest-backup-file}, 3248@code{directory-file-name}, 3249@code{directory-files}, 3250@code{directory-files-and-at@discretionary{}{}{}tributes}, 3251@code{dired-compress-file}, @code{dired-uncache}, 3252@code{exec-path}, @code{expand-file-name}, 3253@code{file-accessible-direc@discretionary{}{}{}tory-p}, 3254@code{file-acl}, 3255@code{file-attributes}, 3256@code{file-direc@discretionary{}{}{}tory-p}, 3257@code{file-equal-p}, 3258@code{file-executable-p}, @code{file-exists-p}, 3259@code{file-in-directory-p}, 3260@code{file-local-copy}, 3261@code{file-modes}, @code{file-name-all-completions}, 3262@code{file-name-as-directory}, 3263@code{file-name-case-insensitive-p}, 3264@code{file-name-completion}, 3265@code{file-name-directory}, 3266@code{file-name-nondirec@discretionary{}{}{}tory}, 3267@code{file-name-sans-versions}, @code{file-newer-than-file-p}, 3268@code{file-notify-add-watch}, @code{file-notify-rm-watch}, 3269@code{file-notify-valid-p}, 3270@code{file-ownership-pre@discretionary{}{}{}served-p}, 3271@code{file-readable-p}, @code{file-regular-p}, 3272@code{file-remote-p}, @code{file-selinux-context}, 3273@code{file-symlink-p}, @code{file-system-info}, 3274@code{file-truename}, @code{file-writable-p}, 3275@code{find-backup-file-name}, 3276@code{get-file-buffer}, 3277@code{insert-directory}, 3278@code{insert-file-contents}, 3279@code{load}, 3280@code{make-auto-save-file-name}, 3281@code{make-direc@discretionary{}{}{}tory}, 3282@code{make-direc@discretionary{}{}{}tory-internal}, 3283@code{make-process}, 3284@code{make-symbolic-link}, 3285@code{process-file}, 3286@code{rename-file}, @code{set-file-acl}, @code{set-file-modes}, 3287@code{set-file-selinux-context}, @code{set-file-times}, 3288@code{set-visited-file-modtime}, @code{shell-command}, 3289@code{start-file-process}, 3290@code{substitute-in-file-name}, 3291@code{unhandled-file-name-directory}, 3292@code{vc-regis@discretionary{}{}{}tered}, 3293@code{verify-visited-file-modtime}, 3294@code{write-region}. 3295@end flushleft 3296@end iftex 3297 3298 Handlers for @code{insert-file-contents} typically need to clear the 3299buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the 3300@var{visit} argument is non-@code{nil}. This also has the effect of 3301unlocking the buffer if it is locked. 3302 3303 The handler function must handle all of the above operations, and 3304possibly others to be added in the future. It need not implement all 3305these operations itself---when it has nothing special to do for a 3306certain operation, it can reinvoke the primitive, to handle the 3307operation in the usual way. It should always reinvoke the primitive 3308for an operation it does not recognize. Here's one way to do this: 3309 3310@smallexample 3311(defun my-file-handler (operation &rest args) 3312 ;; @r{First check for the specific operations} 3313 ;; @r{that we have special handling for.} 3314 (cond ((eq operation 'insert-file-contents) @dots{}) 3315 ((eq operation 'write-region) @dots{}) 3316 @dots{} 3317 ;; @r{Handle any operation we don't know about.} 3318 (t (let ((inhibit-file-name-handlers 3319 (cons 'my-file-handler 3320 (and (eq inhibit-file-name-operation operation) 3321 inhibit-file-name-handlers))) 3322 (inhibit-file-name-operation operation)) 3323 (apply operation args))))) 3324@end smallexample 3325 3326 When a handler function decides to call the ordinary Emacs primitive for 3327the operation at hand, it needs to prevent the primitive from calling 3328the same handler once again, thus leading to an infinite recursion. The 3329example above shows how to do this, with the variables 3330@code{inhibit-file-name-handlers} and 3331@code{inhibit-file-name-operation}. Be careful to use them exactly as 3332shown above; the details are crucial for proper behavior in the case of 3333multiple handlers, and for operations that have two file names that may 3334each have handlers. 3335 3336@kindex safe-magic @r{(property)} 3337 Handlers that don't really do anything special for actual access to the 3338file---such as the ones that implement completion of host names for 3339remote file names---should have a non-@code{nil} @code{safe-magic} 3340property. For instance, Emacs normally protects directory names 3341@c FIXME I don't think this means the PATH environment variable? 3342it finds in @code{PATH} from becoming magic, if they look like magic 3343file names, by prefixing them with @samp{/:}. But if the handler that 3344would be used for them has a non-@code{nil} @code{safe-magic} 3345property, the @samp{/:} is not added. 3346 3347@kindex operations @r{(property)} 3348 A file name handler can have an @code{operations} property to 3349declare which operations it handles in a nontrivial way. If this 3350property has a non-@code{nil} value, it should be a list of 3351operations; then only those operations will call the handler. This 3352avoids inefficiency, but its main purpose is for autoloaded handler 3353functions, so that they won't be loaded except when they have real 3354work to do. 3355 3356 Simply deferring all operations to the usual primitives does not 3357work. For instance, if the file name handler applies to 3358@code{file-exists-p}, then it must handle @code{load} itself, because 3359the usual @code{load} code won't work properly in that case. However, 3360if the handler uses the @code{operations} property to say it doesn't 3361handle @code{file-exists-p}, then it need not handle @code{load} 3362nontrivially. 3363 3364@defvar inhibit-file-name-handlers 3365This variable holds a list of handlers whose use is presently inhibited 3366for a certain operation. 3367@end defvar 3368 3369@defvar inhibit-file-name-operation 3370The operation for which certain handlers are presently inhibited. 3371@end defvar 3372 3373@defun find-file-name-handler file operation 3374This function returns the handler function for file name @var{file}, 3375or @code{nil} if there is none. The argument @var{operation} should 3376be the operation to be performed on the file---the value you will pass 3377to the handler as its first argument when you call it. If 3378@var{operation} equals @code{inhibit-file-name-operation}, or if it is 3379not found in the @code{operations} property of the handler, this 3380function returns @code{nil}. 3381@end defun 3382 3383@defun file-local-copy filename 3384This function copies file @var{filename} to an ordinary non-magic file 3385on the local machine, if it isn't on the local machine already. Magic 3386file names should handle the @code{file-local-copy} operation if they 3387refer to files on other machines. A magic file name that is used for 3388other purposes than remote file access should not handle 3389@code{file-local-copy}; then this function will treat the file as 3390local. 3391 3392If @var{filename} is local, whether magic or not, this function does 3393nothing and returns @code{nil}. Otherwise it returns the file name 3394of the local copy file. 3395@end defun 3396 3397@defun file-remote-p filename &optional identification connected 3398This function tests whether @var{filename} is a remote file. If 3399@var{filename} is local (not remote), the return value is @code{nil}. 3400If @var{filename} is indeed remote, the return value is a string that 3401identifies the remote system. 3402 3403This identifier string can include a host name and a user name, as 3404well as characters designating the method used to access the remote 3405system. For example, the remote identifier string for the filename 3406@code{/sudo::/some/file} is @code{/sudo:root@@localhost:}. 3407 3408If @code{file-remote-p} returns the same identifier for two different 3409filenames, that means they are stored on the same file system and can 3410be accessed locally with respect to each other. This means, for 3411example, that it is possible to start a remote process accessing both 3412files at the same time. Implementers of file name handlers need to 3413ensure this principle is valid. 3414 3415@var{identification} specifies which part of the identifier shall be 3416returned as string. @var{identification} can be the symbol 3417@code{method}, @code{user} or @code{host}; any other value is handled 3418like @code{nil} and means to return the complete identifier string. 3419In the example above, the remote @code{user} identifier string would 3420be @code{root}. 3421 3422If @var{connected} is non-@code{nil}, this function returns @code{nil} 3423even if @var{filename} is remote, if Emacs has no network connection 3424to its host. This is useful when you want to avoid the delay of 3425making connections when they don't exist. 3426@end defun 3427 3428@defun unhandled-file-name-directory filename 3429This function returns the name of a directory that is not magic. For 3430a non-magic @var{filename} it returns the corresponding directory name 3431(@pxref{Directory Names}). For a magic @var{filename}, it invokes the 3432file name handler, which therefore decides what value to return. If 3433@var{filename} is not accessible from a local process, then the file 3434name handler should indicate that by returning @code{nil}. 3435 3436This is useful for running a subprocess; every subprocess must have a 3437non-magic directory to serve as its current directory, and this function 3438is a good way to come up with one. 3439@end defun 3440 3441@cindex local part of remote file name 3442@defun file-local-name filename 3443This function returns the @dfn{local part} of @var{filename}. This is 3444the part of the file's name that identifies it on the remote host, and 3445is typically obtained by removing from the remote file name the parts 3446that specify the remote host and the method of accessing it. For 3447example: 3448 3449@smallexample 3450(file-local-name "/ssh:@var{user}@@@var{host}:/foo/bar") 3451 @result{} "/foo/bar" 3452@end smallexample 3453 3454For a remote @var{filename}, this function returns a file name which 3455could be used directly as an argument of a remote process 3456(@pxref{Asynchronous Processes}, and @pxref{Synchronous Processes}), 3457and as the program to run on the remote host. If @var{filename} is 3458local, this function returns it unchanged. 3459@end defun 3460 3461@defopt remote-file-name-inhibit-cache 3462The attributes of remote files can be cached for better performance. If 3463they are changed outside of Emacs's control, the cached values become 3464invalid, and must be reread. 3465 3466When this variable is set to @code{nil}, cached values are never 3467expired. Use this setting with caution, only if you are sure nothing 3468other than Emacs ever changes the remote files. If it is set to 3469@code{t}, cached values are never used. This is the safest value, but 3470could result in performance degradation. 3471 3472A compromise is to set it to a positive number. This means that 3473cached values are used for that amount of seconds since they were 3474cached. If a remote file is checked regularly, it might be a good 3475idea to let-bind this variable to a value less than the time period 3476between consecutive checks. For example: 3477 3478@example 3479(defun display-time-file-nonempty-p (file) 3480 (let ((remote-file-name-inhibit-cache 3481 (- display-time-interval 5))) 3482 (and (file-exists-p file) 3483 (< 0 (file-attribute-size 3484 (file-attributes 3485 (file-chase-links file))))))) 3486@end example 3487@end defopt 3488 3489@node Format Conversion 3490@section File Format Conversion 3491 3492@cindex file format conversion 3493@cindex encoding file formats 3494@cindex decoding file formats 3495@cindex text properties in files 3496@cindex saving text properties 3497 Emacs performs several steps to convert the data in a buffer (text, 3498text properties, and possibly other information) to and from a 3499representation suitable for storing into a file. This section describes 3500the fundamental functions that perform this @dfn{format conversion}, 3501namely @code{insert-file-contents} for reading a file into a buffer, 3502and @code{write-region} for writing a buffer into a file. 3503 3504@menu 3505* Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}. 3506* Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}. 3507* Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion. 3508@end menu 3509 3510@node Format Conversion Overview 3511@subsection Overview 3512@noindent 3513The function @code{insert-file-contents}: 3514 3515@itemize 3516@item initially, inserts bytes from the file into the buffer; 3517@item decodes bytes to characters as appropriate; 3518@item processes formats as defined by entries in @code{format-alist}; and 3519@item calls functions in @code{after-insert-file-functions}. 3520@end itemize 3521 3522@noindent 3523The function @code{write-region}: 3524 3525@itemize 3526@item initially, calls functions in @code{write-region-annotate-functions}; 3527@item processes formats as defined by entries in @code{format-alist}; 3528@item encodes characters to bytes as appropriate; and 3529@item modifies the file with the bytes. 3530@end itemize 3531 3532 This shows the symmetry of the lowest-level operations; reading and 3533writing handle things in opposite order. The rest of this section 3534describes the two facilities surrounding the three variables named 3535above, as well as some related functions. @ref{Coding Systems}, for 3536details on character encoding and decoding. 3537 3538@node Format Conversion Round-Trip 3539@subsection Round-Trip Specification 3540 3541 The most general of the two facilities is controlled by the variable 3542@code{format-alist}, a list of @dfn{file format} specifications, which 3543describe textual representations used in files for the data in an Emacs 3544buffer. The descriptions for reading and writing are paired, which is 3545why we call this ``round-trip'' specification 3546(@pxref{Format Conversion Piecemeal}, for non-paired specification). 3547 3548@defvar format-alist 3549This list contains one format definition for each defined file format. 3550Each format definition is a list of this form: 3551 3552@example 3553(@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve}) 3554@end example 3555@end defvar 3556 3557@cindex format definition 3558@noindent 3559Here is what the elements in a format definition mean: 3560 3561@table @var 3562@item name 3563The name of this format. 3564 3565@item doc-string 3566A documentation string for the format. 3567 3568@item regexp 3569A regular expression which is used to recognize files represented in 3570this format. If @code{nil}, the format is never applied automatically. 3571 3572@item from-fn 3573A shell command or function to decode data in this format (to convert 3574file data into the usual Emacs data representation). 3575 3576A shell command is represented as a string; Emacs runs the command as a 3577filter to perform the conversion. 3578 3579If @var{from-fn} is a function, it is called with two arguments, @var{begin} 3580and @var{end}, which specify the part of the buffer it should convert. 3581It should convert the text by editing it in place. Since this can 3582change the length of the text, @var{from-fn} should return the modified 3583end position. 3584 3585One responsibility of @var{from-fn} is to make sure that the beginning 3586of the file no longer matches @var{regexp}. Otherwise it is likely to 3587get called again. Also, @var{from-fn} must not involve buffers or 3588files other than the one being decoded, otherwise the internal buffer 3589used for formatting might be overwritten. 3590 3591@item to-fn 3592A shell command or function to encode data in this format---that is, to 3593convert the usual Emacs data representation into this format. 3594 3595If @var{to-fn} is a string, it is a shell command; Emacs runs the 3596command as a filter to perform the conversion. 3597 3598If @var{to-fn} is a function, it is called with three arguments: 3599@var{begin} and @var{end}, which specify the part of the buffer it 3600should convert, and @var{buffer}, which specifies which buffer. There 3601are two ways it can do the conversion: 3602 3603@itemize @bullet 3604@item 3605By editing the buffer in place. In this case, @var{to-fn} should 3606return the end-position of the range of text, as modified. 3607 3608@item 3609By returning a list of annotations. This is a list of elements of the 3610form @code{(@var{position} . @var{string})}, where @var{position} is an 3611integer specifying the relative position in the text to be written, and 3612@var{string} is the annotation to add there. The list must be sorted in 3613order of position when @var{to-fn} returns it. 3614 3615When @code{write-region} actually writes the text from the buffer to the 3616file, it intermixes the specified annotations at the corresponding 3617positions. All this takes place without modifying the buffer. 3618@end itemize 3619 3620@var{to-fn} must not involve buffers or files other than the one being 3621encoded, otherwise the internal buffer used for formatting might be 3622overwritten. 3623 3624@item modify 3625A flag, @code{t} if the encoding function modifies the buffer, and 3626@code{nil} if it works by returning a list of annotations. 3627 3628@item mode-fn 3629A minor-mode function to call after visiting a file converted from this 3630format. The function is called with one argument, the integer 1; 3631that tells a minor-mode function to enable the mode. 3632 3633@item preserve 3634A flag, @code{t} if @code{format-write-file} should not remove this format 3635from @code{buffer-file-format}. 3636@end table 3637 3638The function @code{insert-file-contents} automatically recognizes file 3639formats when it reads the specified file. It checks the text of the 3640beginning of the file against the regular expressions of the format 3641definitions, and if it finds a match, it calls the decoding function for 3642that format. Then it checks all the known formats over again. 3643It keeps checking them until none of them is applicable. 3644 3645Visiting a file, with @code{find-file-noselect} or the commands that use 3646it, performs conversion likewise (because it calls 3647@code{insert-file-contents}); it also calls the mode function for each 3648format that it decodes. It stores a list of the format names in the 3649buffer-local variable @code{buffer-file-format}. 3650 3651@defvar buffer-file-format 3652This variable states the format of the visited file. More precisely, 3653this is a list of the file format names that were decoded in the course 3654of visiting the current buffer's file. It is always buffer-local in all 3655buffers. 3656@end defvar 3657 3658When @code{write-region} writes data into a file, it first calls the 3659encoding functions for the formats listed in @code{buffer-file-format}, 3660in the order of appearance in the list. 3661 3662@deffn Command format-write-file file format &optional confirm 3663This command writes the current buffer contents into the file @var{file} 3664in a format based on @var{format}, which is a list of format names. It 3665constructs the actual format starting from @var{format}, then appending 3666any elements from the value of @code{buffer-file-format} with a 3667non-@code{nil} @var{preserve} flag (see above), if they are not already 3668present in @var{format}. It then updates @code{buffer-file-format} with 3669this format, making it the default for future saves. Except for the 3670@var{format} argument, this command is similar to @code{write-file}. In 3671particular, @var{confirm} has the same meaning and interactive treatment 3672as the corresponding argument to @code{write-file}. @xref{Definition of 3673write-file}. 3674@end deffn 3675 3676@deffn Command format-find-file file format 3677This command finds the file @var{file}, converting it according to 3678format @var{format}. It also makes @var{format} the default if the 3679buffer is saved later. 3680 3681The argument @var{format} is a list of format names. If @var{format} is 3682@code{nil}, no conversion takes place. Interactively, typing just 3683@key{RET} for @var{format} specifies @code{nil}. 3684@end deffn 3685 3686@deffn Command format-insert-file file format &optional beg end 3687This command inserts the contents of file @var{file}, converting it 3688according to format @var{format}. If @var{beg} and @var{end} are 3689non-@code{nil}, they specify which part of the file to read, as in 3690@code{insert-file-contents} (@pxref{Reading from Files}). 3691 3692The return value is like what @code{insert-file-contents} returns: a 3693list of the absolute file name and the length of the data inserted 3694(after conversion). 3695 3696The argument @var{format} is a list of format names. If @var{format} is 3697@code{nil}, no conversion takes place. Interactively, typing just 3698@key{RET} for @var{format} specifies @code{nil}. 3699@end deffn 3700 3701@defvar buffer-auto-save-file-format 3702This variable specifies the format to use for auto-saving. Its value is 3703a list of format names, just like the value of 3704@code{buffer-file-format}; however, it is used instead of 3705@code{buffer-file-format} for writing auto-save files. If the value 3706is @code{t}, the default, auto-saving uses the same format as a 3707regular save in the same buffer. This variable is always buffer-local 3708in all buffers. 3709@end defvar 3710 3711@node Format Conversion Piecemeal 3712@subsection Piecemeal Specification 3713 3714 In contrast to the round-trip specification described in the previous 3715subsection (@pxref{Format Conversion Round-Trip}), you can use the variables 3716@code{after-insert-file-functions} and @code{write-region-annotate-functions} 3717to separately control the respective reading and writing conversions. 3718 3719 Conversion starts with one representation and produces another 3720representation. When there is only one conversion to do, there is no 3721conflict about what to start with. However, when there are multiple 3722conversions involved, conflict may arise when two conversions need to 3723start with the same data. 3724 3725 This situation is best understood in the context of converting text 3726properties during @code{write-region}. For example, the character at 3727position 42 in a buffer is @samp{X} with a text property @code{foo}. If 3728the conversion for @code{foo} is done by inserting into the buffer, say, 3729@samp{FOO:}, then that changes the character at position 42 from 3730@samp{X} to @samp{F}. The next conversion will start with the wrong 3731data straight away. 3732 3733 To avoid conflict, cooperative conversions do not modify the buffer, 3734but instead specify @dfn{annotations}, a list of elements of the form 3735@code{(@var{position} . @var{string})}, sorted in order of increasing 3736@var{position}. 3737 3738 If there is more than one conversion, @code{write-region} merges their 3739annotations destructively into one sorted list. Later, when the text 3740from the buffer is actually written to the file, it intermixes the 3741specified annotations at the corresponding positions. All this takes 3742place without modifying the buffer. 3743 3744@c ??? What about "overriding" conversions like those allowed 3745@c ??? for 'write-region-annotate-functions', below? --ttn 3746 3747 In contrast, when reading, the annotations intermixed with the text 3748are handled immediately. @code{insert-file-contents} sets point to 3749the beginning of some text to be converted, then calls the conversion 3750functions with the length of that text. These functions should always 3751return with point at the beginning of the inserted text. This 3752approach makes sense for reading because annotations removed by the 3753first converter can't be mistakenly processed by a later converter. 3754Each conversion function should scan for the annotations it 3755recognizes, remove the annotation, modify the buffer text (to set a 3756text property, for example), and return the updated length of the 3757text, as it stands after those changes. The value returned by one 3758function becomes the argument to the next function. 3759 3760@defvar write-region-annotate-functions 3761A list of functions for @code{write-region} to call. Each function in 3762the list is called with two arguments: the start and end of the region 3763to be written. These functions should not alter the contents of the 3764buffer. Instead, they should return annotations. 3765 3766As a special case, a function may return with a different buffer 3767current. Emacs takes this to mean that the current buffer contains 3768altered text to be output. It therefore changes the @var{start} and 3769@var{end} arguments of the @code{write-region} call, giving them the 3770values of @code{point-min} and @code{point-max} in the new buffer, 3771respectively. It also discards all previous annotations, because they 3772should have been dealt with by this function. 3773@end defvar 3774 3775@defvar write-region-post-annotation-function 3776The value of this variable, if non-@code{nil}, should be a function. 3777This function is called, with no arguments, after @code{write-region} 3778has completed. 3779 3780If any function in @code{write-region-annotate-functions} returns with 3781a different buffer current, Emacs calls 3782@code{write-region-post-annotation-function} more than once. Emacs 3783calls it with the last buffer that was current, and again with the 3784buffer before that, and so on back to the original buffer. 3785 3786Thus, a function in @code{write-region-annotate-functions} can create 3787a buffer, give this variable the local value of @code{kill-buffer} in 3788that buffer, set up the buffer with altered text, and make the buffer 3789current. The buffer will be killed after @code{write-region} is done. 3790@end defvar 3791 3792@defvar after-insert-file-functions 3793Each function in this list is called by @code{insert-file-contents} 3794with one argument, the number of characters inserted, and with point 3795at the beginning of the inserted text. Each function should leave 3796point unchanged, and return the new character count describing the 3797inserted text as modified by the function. 3798@c ??? The docstring mentions a handler from 'file-name-handler-alist' 3799@c "intercepting" 'insert-file-contents'. Hmmm. --ttn 3800@end defvar 3801 3802 We invite users to write Lisp programs to store and retrieve text 3803properties in files, using these hooks, and thus to experiment with 3804various data formats and find good ones. Eventually we hope users 3805will produce good, general extensions we can install in Emacs. 3806 3807 We suggest not trying to handle arbitrary Lisp objects as text property 3808names or values---because a program that general is probably difficult 3809to write, and slow. Instead, choose a set of possible data types that 3810are reasonably flexible, and not too hard to encode. 3811