| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, |
| 4 | @c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 |
| 5 | @c Free Software Foundation, Inc. |
| 6 | @c See the file elisp.texi for copying conditions. |
| 7 | @setfilename ../../info/files |
| 8 | @node Files, Backups and Auto-Saving, Documentation, Top |
| 9 | @comment node-name, next, previous, up |
| 10 | @chapter Files |
| 11 | |
| 12 | In Emacs, you can find, create, view, save, and otherwise work with |
| 13 | files and file directories. This chapter describes most of the |
| 14 | file-related functions of Emacs Lisp, but a few others are described in |
| 15 | @ref{Buffers}, and those related to backups and auto-saving are |
| 16 | described in @ref{Backups and Auto-Saving}. |
| 17 | |
| 18 | Many of the file functions take one or more arguments that are file |
| 19 | names. A file name is actually a string. Most of these functions |
| 20 | expand file name arguments by calling @code{expand-file-name}, so that |
| 21 | @file{~} is handled correctly, as are relative file names (including |
| 22 | @samp{../}). These functions don't recognize environment variable |
| 23 | substitutions such as @samp{$HOME}. @xref{File Name Expansion}. |
| 24 | |
| 25 | When file I/O functions signal Lisp errors, they usually use the |
| 26 | condition @code{file-error} (@pxref{Handling Errors}). The error |
| 27 | message is in most cases obtained from the operating system, according |
| 28 | to locale @code{system-message-locale}, and decoded using coding system |
| 29 | @code{locale-coding-system} (@pxref{Locales}). |
| 30 | |
| 31 | @menu |
| 32 | * Visiting Files:: Reading files into Emacs buffers for editing. |
| 33 | * Saving Buffers:: Writing changed buffers back into files. |
| 34 | * Reading from Files:: Reading files into buffers without visiting. |
| 35 | * Writing to Files:: Writing new files from parts of buffers. |
| 36 | * File Locks:: Locking and unlocking files, to prevent |
| 37 | simultaneous editing by two people. |
| 38 | * Information about Files:: Testing existence, accessibility, size of files. |
| 39 | * Changing Files:: Renaming files, changing protection, etc. |
| 40 | * File Names:: Decomposing and expanding file names. |
| 41 | * Contents of Directories:: Getting a list of the files in a directory. |
| 42 | * Create/Delete Dirs:: Creating and Deleting Directories. |
| 43 | * Magic File Names:: Defining "magic" special handling |
| 44 | for certain file names. |
| 45 | * Format Conversion:: Conversion to and from various file formats. |
| 46 | @end menu |
| 47 | |
| 48 | @node Visiting Files |
| 49 | @section Visiting Files |
| 50 | @cindex finding files |
| 51 | @cindex visiting files |
| 52 | |
| 53 | Visiting a file means reading a file into a buffer. Once this is |
| 54 | done, we say that the buffer is @dfn{visiting} that file, and call the |
| 55 | file ``the visited file'' of the buffer. |
| 56 | |
| 57 | A file and a buffer are two different things. A file is information |
| 58 | recorded permanently in the computer (unless you delete it). A buffer, |
| 59 | on the other hand, is information inside of Emacs that will vanish at |
| 60 | the end of the editing session (or when you kill the buffer). Usually, |
| 61 | a buffer contains information that you have copied from a file; then we |
| 62 | say the buffer is visiting that file. The copy in the buffer is what |
| 63 | you modify with editing commands. Such changes to the buffer do not |
| 64 | change the file; therefore, to make the changes permanent, you must |
| 65 | @dfn{save} the buffer, which means copying the altered buffer contents |
| 66 | back into the file. |
| 67 | |
| 68 | In spite of the distinction between files and buffers, people often |
| 69 | refer to a file when they mean a buffer and vice-versa. Indeed, we say, |
| 70 | ``I am editing a file,'' rather than, ``I am editing a buffer that I |
| 71 | will soon save as a file of the same name.'' Humans do not usually need |
| 72 | to make the distinction explicit. When dealing with a computer program, |
| 73 | however, it is good to keep the distinction in mind. |
| 74 | |
| 75 | @menu |
| 76 | * Visiting Functions:: The usual interface functions for visiting. |
| 77 | * Subroutines of Visiting:: Lower-level subroutines that they use. |
| 78 | @end menu |
| 79 | |
| 80 | @node Visiting Functions |
| 81 | @subsection Functions for Visiting Files |
| 82 | |
| 83 | This section describes the functions normally used to visit files. |
| 84 | For historical reasons, these functions have names starting with |
| 85 | @samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for |
| 86 | functions and variables that access the visited file name of a buffer or |
| 87 | that find an existing buffer by its visited file name. |
| 88 | |
| 89 | In a Lisp program, if you want to look at the contents of a file but |
| 90 | not alter it, the fastest way is to use @code{insert-file-contents} in a |
| 91 | temporary buffer. Visiting the file is not necessary and takes longer. |
| 92 | @xref{Reading from Files}. |
| 93 | |
| 94 | @deffn Command find-file filename &optional wildcards |
| 95 | This command selects a buffer visiting the file @var{filename}, |
| 96 | using an existing buffer if there is one, and otherwise creating a |
| 97 | new buffer and reading the file into it. It also returns that buffer. |
| 98 | |
| 99 | Aside from some technical details, the body of the @code{find-file} |
| 100 | function is basically equivalent to: |
| 101 | |
| 102 | @smallexample |
| 103 | (switch-to-buffer (find-file-noselect filename nil nil wildcards)) |
| 104 | @end smallexample |
| 105 | |
| 106 | @noindent |
| 107 | (See @code{switch-to-buffer} in @ref{Displaying Buffers}.) |
| 108 | |
| 109 | If @var{wildcards} is non-@code{nil}, which is always true in an |
| 110 | interactive call, then @code{find-file} expands wildcard characters in |
| 111 | @var{filename} and visits all the matching files. |
| 112 | |
| 113 | When @code{find-file} is called interactively, it prompts for |
| 114 | @var{filename} in the minibuffer. |
| 115 | @end deffn |
| 116 | |
| 117 | @defun find-file-noselect filename &optional nowarn rawfile wildcards |
| 118 | This function is the guts of all the file-visiting functions. It |
| 119 | returns a buffer visiting the file @var{filename}. You may make the |
| 120 | buffer current or display it in a window if you wish, but this |
| 121 | function does not do so. |
| 122 | |
| 123 | The function returns an existing buffer if there is one; otherwise it |
| 124 | creates a new buffer and reads the file into it. When |
| 125 | @code{find-file-noselect} uses an existing buffer, it first verifies |
| 126 | that the file has not changed since it was last visited or saved in |
| 127 | that buffer. If the file has changed, this function asks the user |
| 128 | whether to reread the changed file. If the user says @samp{yes}, any |
| 129 | edits previously made in the buffer are lost. |
| 130 | |
| 131 | Reading the file involves decoding the file's contents (@pxref{Coding |
| 132 | Systems}), including end-of-line conversion, and format conversion |
| 133 | (@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil}, |
| 134 | then @code{find-file-noselect} expands wildcard characters in |
| 135 | @var{filename} and visits all the matching files. |
| 136 | |
| 137 | This function displays warning or advisory messages in various peculiar |
| 138 | cases, unless the optional argument @var{nowarn} is non-@code{nil}. For |
| 139 | example, if it needs to create a buffer, and there is no file named |
| 140 | @var{filename}, it displays the message @samp{(New file)} in the echo |
| 141 | area, and leaves the buffer empty. |
| 142 | |
| 143 | The @code{find-file-noselect} function normally calls |
| 144 | @code{after-find-file} after reading the file (@pxref{Subroutines of |
| 145 | Visiting}). That function sets the buffer major mode, parses local |
| 146 | variables, warns the user if there exists an auto-save file more recent |
| 147 | than the file just visited, and finishes by running the functions in |
| 148 | @code{find-file-hook}. |
| 149 | |
| 150 | If the optional argument @var{rawfile} is non-@code{nil}, then |
| 151 | @code{after-find-file} is not called, and the |
| 152 | @code{find-file-not-found-functions} are not run in case of failure. |
| 153 | What's more, a non-@code{nil} @var{rawfile} value suppresses coding |
| 154 | system conversion and format conversion. |
| 155 | |
| 156 | The @code{find-file-noselect} function usually returns the buffer that |
| 157 | is visiting the file @var{filename}. But, if wildcards are actually |
| 158 | used and expanded, it returns a list of buffers that are visiting the |
| 159 | various files. |
| 160 | |
| 161 | @example |
| 162 | @group |
| 163 | (find-file-noselect "/etc/fstab") |
| 164 | @result{} #<buffer fstab> |
| 165 | @end group |
| 166 | @end example |
| 167 | @end defun |
| 168 | |
| 169 | @deffn Command find-file-other-window filename &optional wildcards |
| 170 | This command selects a buffer visiting the file @var{filename}, but |
| 171 | does so in a window other than the selected window. It may use another |
| 172 | existing window or split a window; see @ref{Displaying Buffers}. |
| 173 | |
| 174 | When this command is called interactively, it prompts for |
| 175 | @var{filename}. |
| 176 | @end deffn |
| 177 | |
| 178 | @deffn Command find-file-read-only filename &optional wildcards |
| 179 | This command selects a buffer visiting the file @var{filename}, like |
| 180 | @code{find-file}, but it marks the buffer as read-only. @xref{Read Only |
| 181 | Buffers}, for related functions and variables. |
| 182 | |
| 183 | When this command is called interactively, it prompts for |
| 184 | @var{filename}. |
| 185 | @end deffn |
| 186 | |
| 187 | @deffn Command view-file filename |
| 188 | This command visits @var{filename} using View mode, returning to the |
| 189 | previous buffer when you exit View mode. View mode is a minor mode that |
| 190 | provides commands to skim rapidly through the file, but does not let you |
| 191 | modify the text. Entering View mode runs the normal hook |
| 192 | @code{view-mode-hook}. @xref{Hooks}. |
| 193 | |
| 194 | When @code{view-file} is called interactively, it prompts for |
| 195 | @var{filename}. |
| 196 | @end deffn |
| 197 | |
| 198 | @defopt find-file-wildcards |
| 199 | If this variable is non-@code{nil}, then the various @code{find-file} |
| 200 | commands check for wildcard characters and visit all the files that |
| 201 | match them (when invoked interactively or when their @var{wildcards} |
| 202 | argument is non-@code{nil}). If this option is @code{nil}, then |
| 203 | the @code{find-file} commands ignore their @var{wildcards} argument |
| 204 | and never treat wildcard characters specially. |
| 205 | @end defopt |
| 206 | |
| 207 | @defopt find-file-hook |
| 208 | The value of this variable is a list of functions to be called after a |
| 209 | file is visited. The file's local-variables specification (if any) will |
| 210 | have been processed before the hooks are run. The buffer visiting the |
| 211 | file is current when the hook functions are run. |
| 212 | |
| 213 | This variable is a normal hook. @xref{Hooks}. |
| 214 | @end defopt |
| 215 | |
| 216 | @defvar find-file-not-found-functions |
| 217 | The value of this variable is a list of functions to be called when |
| 218 | @code{find-file} or @code{find-file-noselect} is passed a nonexistent |
| 219 | file name. @code{find-file-noselect} calls these functions as soon as |
| 220 | it detects a nonexistent file. It calls them in the order of the list, |
| 221 | until one of them returns non-@code{nil}. @code{buffer-file-name} is |
| 222 | already set up. |
| 223 | |
| 224 | This is not a normal hook because the values of the functions are |
| 225 | used, and in many cases only some of the functions are called. |
| 226 | @end defvar |
| 227 | |
| 228 | @node Subroutines of Visiting |
| 229 | @comment node-name, next, previous, up |
| 230 | @subsection Subroutines of Visiting |
| 231 | |
| 232 | The @code{find-file-noselect} function uses two important subroutines |
| 233 | which are sometimes useful in user Lisp code: @code{create-file-buffer} |
| 234 | and @code{after-find-file}. This section explains how to use them. |
| 235 | |
| 236 | @defun create-file-buffer filename |
| 237 | This function creates a suitably named buffer for visiting |
| 238 | @var{filename}, and returns it. It uses @var{filename} (sans directory) |
| 239 | as the name if that name is free; otherwise, it appends a string such as |
| 240 | @samp{<2>} to get an unused name. See also @ref{Creating Buffers}. |
| 241 | |
| 242 | @strong{Please note:} @code{create-file-buffer} does @emph{not} |
| 243 | associate the new buffer with a file and does not select the buffer. |
| 244 | It also does not use the default major mode. |
| 245 | |
| 246 | @example |
| 247 | @group |
| 248 | (create-file-buffer "foo") |
| 249 | @result{} #<buffer foo> |
| 250 | @end group |
| 251 | @group |
| 252 | (create-file-buffer "foo") |
| 253 | @result{} #<buffer foo<2>> |
| 254 | @end group |
| 255 | @group |
| 256 | (create-file-buffer "foo") |
| 257 | @result{} #<buffer foo<3>> |
| 258 | @end group |
| 259 | @end example |
| 260 | |
| 261 | This function is used by @code{find-file-noselect}. |
| 262 | It uses @code{generate-new-buffer} (@pxref{Creating Buffers}). |
| 263 | @end defun |
| 264 | |
| 265 | @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes |
| 266 | This function sets the buffer major mode, and parses local variables |
| 267 | (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect} |
| 268 | and by the default revert function (@pxref{Reverting}). |
| 269 | |
| 270 | @cindex new file message |
| 271 | @cindex file open error |
| 272 | If reading the file got an error because the file does not exist, but |
| 273 | its directory does exist, the caller should pass a non-@code{nil} value |
| 274 | for @var{error}. In that case, @code{after-find-file} issues a warning: |
| 275 | @samp{(New file)}. For more serious errors, the caller should usually not |
| 276 | call @code{after-find-file}. |
| 277 | |
| 278 | If @var{warn} is non-@code{nil}, then this function issues a warning |
| 279 | if an auto-save file exists and is more recent than the visited file. |
| 280 | |
| 281 | If @var{noauto} is non-@code{nil}, that says not to enable or disable |
| 282 | Auto-Save mode. The mode remains enabled if it was enabled before. |
| 283 | |
| 284 | If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that |
| 285 | means this call was from @code{revert-buffer}. This has no direct |
| 286 | effect, but some mode functions and hook functions check the value |
| 287 | of this variable. |
| 288 | |
| 289 | If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's |
| 290 | major mode, don't process local variables specifications in the file, |
| 291 | and don't run @code{find-file-hook}. This feature is used by |
| 292 | @code{revert-buffer} in some cases. |
| 293 | |
| 294 | The last thing @code{after-find-file} does is call all the functions |
| 295 | in the list @code{find-file-hook}. |
| 296 | @end defun |
| 297 | |
| 298 | @node Saving Buffers |
| 299 | @section Saving Buffers |
| 300 | @cindex saving buffers |
| 301 | |
| 302 | When you edit a file in Emacs, you are actually working on a buffer |
| 303 | that is visiting that file---that is, the contents of the file are |
| 304 | copied into the buffer and the copy is what you edit. Changes to the |
| 305 | buffer do not change the file until you @dfn{save} the buffer, which |
| 306 | means copying the contents of the buffer into the file. |
| 307 | |
| 308 | @deffn Command save-buffer &optional backup-option |
| 309 | This function saves the contents of the current buffer in its visited |
| 310 | file if the buffer has been modified since it was last visited or saved. |
| 311 | Otherwise it does nothing. |
| 312 | |
| 313 | @code{save-buffer} is responsible for making backup files. Normally, |
| 314 | @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup |
| 315 | file only if this is the first save since visiting the file. Other |
| 316 | values for @var{backup-option} request the making of backup files in |
| 317 | other circumstances: |
| 318 | |
| 319 | @itemize @bullet |
| 320 | @item |
| 321 | With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the |
| 322 | @code{save-buffer} function marks this version of the file to be |
| 323 | backed up when the buffer is next saved. |
| 324 | |
| 325 | @item |
| 326 | With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the |
| 327 | @code{save-buffer} function unconditionally backs up the previous |
| 328 | version of the file before saving it. |
| 329 | |
| 330 | @item |
| 331 | With an argument of 0, unconditionally do @emph{not} make any backup file. |
| 332 | @end itemize |
| 333 | @end deffn |
| 334 | |
| 335 | @deffn Command save-some-buffers &optional save-silently-p pred |
| 336 | @anchor{Definition of save-some-buffers} |
| 337 | This command saves some modified file-visiting buffers. Normally it |
| 338 | asks the user about each buffer. But if @var{save-silently-p} is |
| 339 | non-@code{nil}, it saves all the file-visiting buffers without querying |
| 340 | the user. |
| 341 | |
| 342 | The optional @var{pred} argument controls which buffers to ask about |
| 343 | (or to save silently if @var{save-silently-p} is non-@code{nil}). |
| 344 | If it is @code{nil}, that means to ask only about file-visiting buffers. |
| 345 | If it is @code{t}, that means also offer to save certain other non-file |
| 346 | buffers---those that have a non-@code{nil} buffer-local value of |
| 347 | @code{buffer-offer-save} (@pxref{Killing Buffers}). A user who says |
| 348 | @samp{yes} to saving a non-file buffer is asked to specify the file |
| 349 | name to use. The @code{save-buffers-kill-emacs} function passes the |
| 350 | value @code{t} for @var{pred}. |
| 351 | |
| 352 | If @var{pred} is neither @code{t} nor @code{nil}, then it should be |
| 353 | a function of no arguments. It will be called in each buffer to decide |
| 354 | whether to offer to save that buffer. If it returns a non-@code{nil} |
| 355 | value in a certain buffer, that means do offer to save that buffer. |
| 356 | @end deffn |
| 357 | |
| 358 | @deffn Command write-file filename &optional confirm |
| 359 | @anchor{Definition of write-file} |
| 360 | This function writes the current buffer into file @var{filename}, makes |
| 361 | the buffer visit that file, and marks it not modified. Then it renames |
| 362 | the buffer based on @var{filename}, appending a string like @samp{<2>} |
| 363 | if necessary to make a unique buffer name. It does most of this work by |
| 364 | calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and |
| 365 | @code{save-buffer}. |
| 366 | |
| 367 | If @var{confirm} is non-@code{nil}, that means to ask for confirmation |
| 368 | before overwriting an existing file. Interactively, confirmation is |
| 369 | required, unless the user supplies a prefix argument. |
| 370 | |
| 371 | If @var{filename} is an existing directory, or a symbolic link to one, |
| 372 | @code{write-file} uses the name of the visited file, in directory |
| 373 | @var{filename}. If the buffer is not visiting a file, it uses the |
| 374 | buffer name instead. |
| 375 | @end deffn |
| 376 | |
| 377 | Saving a buffer runs several hooks. It also performs format |
| 378 | conversion (@pxref{Format Conversion}). |
| 379 | |
| 380 | @defvar write-file-functions |
| 381 | The value of this variable is a list of functions to be called before |
| 382 | writing out a buffer to its visited file. If one of them returns |
| 383 | non-@code{nil}, the file is considered already written and the rest of |
| 384 | the functions are not called, nor is the usual code for writing the file |
| 385 | executed. |
| 386 | |
| 387 | If a function in @code{write-file-functions} returns non-@code{nil}, it |
| 388 | is responsible for making a backup file (if that is appropriate). |
| 389 | To do so, execute the following code: |
| 390 | |
| 391 | @example |
| 392 | (or buffer-backed-up (backup-buffer)) |
| 393 | @end example |
| 394 | |
| 395 | You might wish to save the file modes value returned by |
| 396 | @code{backup-buffer} and use that (if non-@code{nil}) to set the mode |
| 397 | bits of the file that you write. This is what @code{save-buffer} |
| 398 | normally does. @xref{Making Backups,, Making Backup Files}. |
| 399 | |
| 400 | The hook functions in @code{write-file-functions} are also responsible |
| 401 | for encoding the data (if desired): they must choose a suitable coding |
| 402 | system and end-of-line conversion (@pxref{Lisp and Coding Systems}), |
| 403 | perform the encoding (@pxref{Explicit Encoding}), and set |
| 404 | @code{last-coding-system-used} to the coding system that was used |
| 405 | (@pxref{Encoding and I/O}). |
| 406 | |
| 407 | If you set this hook locally in a buffer, it is assumed to be |
| 408 | associated with the file or the way the contents of the buffer were |
| 409 | obtained. Thus the variable is marked as a permanent local, so that |
| 410 | changing the major mode does not alter a buffer-local value. On the |
| 411 | other hand, calling @code{set-visited-file-name} will reset it. |
| 412 | If this is not what you want, you might like to use |
| 413 | @code{write-contents-functions} instead. |
| 414 | |
| 415 | Even though this is not a normal hook, you can use @code{add-hook} and |
| 416 | @code{remove-hook} to manipulate the list. @xref{Hooks}. |
| 417 | @end defvar |
| 418 | |
| 419 | @c Emacs 19 feature |
| 420 | @defvar write-contents-functions |
| 421 | This works just like @code{write-file-functions}, but it is intended |
| 422 | for hooks that pertain to the buffer's contents, not to the particular |
| 423 | visited file or its location. Such hooks are usually set up by major |
| 424 | modes, as buffer-local bindings for this variable. This variable |
| 425 | automatically becomes buffer-local whenever it is set; switching to a |
| 426 | new major mode always resets this variable, but calling |
| 427 | @code{set-visited-file-name} does not. |
| 428 | |
| 429 | If any of the functions in this hook returns non-@code{nil}, the file |
| 430 | is considered already written and the rest are not called and neither |
| 431 | are the functions in @code{write-file-functions}. |
| 432 | @end defvar |
| 433 | |
| 434 | @defopt before-save-hook |
| 435 | This normal hook runs before a buffer is saved in its visited file, |
| 436 | regardless of whether that is done normally or by one of the hooks |
| 437 | described above. For instance, the @file{copyright.el} program uses |
| 438 | this hook to make sure the file you are saving has the current year in |
| 439 | its copyright notice. |
| 440 | @end defopt |
| 441 | |
| 442 | @c Emacs 19 feature |
| 443 | @defopt after-save-hook |
| 444 | This normal hook runs after a buffer has been saved in its visited file. |
| 445 | One use of this hook is in Fast Lock mode; it uses this hook to save the |
| 446 | highlighting information in a cache file. |
| 447 | @end defopt |
| 448 | |
| 449 | @defopt file-precious-flag |
| 450 | If this variable is non-@code{nil}, then @code{save-buffer} protects |
| 451 | against I/O errors while saving by writing the new file to a temporary |
| 452 | name instead of the name it is supposed to have, and then renaming it to |
| 453 | the intended name after it is clear there are no errors. This procedure |
| 454 | prevents problems such as a lack of disk space from resulting in an |
| 455 | invalid file. |
| 456 | |
| 457 | As a side effect, backups are necessarily made by copying. @xref{Rename |
| 458 | or Copy}. Yet, at the same time, saving a precious file always breaks |
| 459 | all hard links between the file you save and other file names. |
| 460 | |
| 461 | Some modes give this variable a non-@code{nil} buffer-local value |
| 462 | in particular buffers. |
| 463 | @end defopt |
| 464 | |
| 465 | @defopt require-final-newline |
| 466 | This variable determines whether files may be written out that do |
| 467 | @emph{not} end with a newline. If the value of the variable is |
| 468 | @code{t}, then @code{save-buffer} silently adds a newline at the end of |
| 469 | the file whenever the buffer being saved does not already end in one. |
| 470 | If the value of the variable is non-@code{nil}, but not @code{t}, then |
| 471 | @code{save-buffer} asks the user whether to add a newline each time the |
| 472 | case arises. |
| 473 | |
| 474 | If the value of the variable is @code{nil}, then @code{save-buffer} |
| 475 | doesn't add newlines at all. @code{nil} is the default value, but a few |
| 476 | major modes set it to @code{t} in particular buffers. |
| 477 | @end defopt |
| 478 | |
| 479 | See also the function @code{set-visited-file-name} (@pxref{Buffer File |
| 480 | Name}). |
| 481 | |
| 482 | @node Reading from Files |
| 483 | @comment node-name, next, previous, up |
| 484 | @section Reading from Files |
| 485 | @cindex reading from files |
| 486 | |
| 487 | You can copy a file from the disk and insert it into a buffer |
| 488 | using the @code{insert-file-contents} function. Don't use the user-level |
| 489 | command @code{insert-file} in a Lisp program, as that sets the mark. |
| 490 | |
| 491 | @defun insert-file-contents filename &optional visit beg end replace |
| 492 | This function inserts the contents of file @var{filename} into the |
| 493 | current buffer after point. It returns a list of the absolute file name |
| 494 | and the length of the data inserted. An error is signaled if |
| 495 | @var{filename} is not the name of a file that can be read. |
| 496 | |
| 497 | The function @code{insert-file-contents} checks the file contents |
| 498 | against the defined file formats, and converts the file contents if |
| 499 | appropriate and also calls the functions in |
| 500 | the list @code{after-insert-file-functions}. @xref{Format Conversion}. |
| 501 | Normally, one of the functions in the |
| 502 | @code{after-insert-file-functions} list determines the coding system |
| 503 | (@pxref{Coding Systems}) used for decoding the file's contents, |
| 504 | including end-of-line conversion. However, if the file contains null |
| 505 | bytes, it is by default visited without any code conversions; see |
| 506 | @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to |
| 507 | control this behavior. |
| 508 | |
| 509 | If @var{visit} is non-@code{nil}, this function additionally marks the |
| 510 | buffer as unmodified and sets up various fields in the buffer so that it |
| 511 | is visiting the file @var{filename}: these include the buffer's visited |
| 512 | file name and its last save file modtime. This feature is used by |
| 513 | @code{find-file-noselect} and you probably should not use it yourself. |
| 514 | |
| 515 | If @var{beg} and @var{end} are non-@code{nil}, they should be integers |
| 516 | specifying the portion of the file to insert. In this case, @var{visit} |
| 517 | must be @code{nil}. For example, |
| 518 | |
| 519 | @example |
| 520 | (insert-file-contents filename nil 0 500) |
| 521 | @end example |
| 522 | |
| 523 | @noindent |
| 524 | inserts the first 500 characters of a file. |
| 525 | |
| 526 | If the argument @var{replace} is non-@code{nil}, it means to replace the |
| 527 | contents of the buffer (actually, just the accessible portion) with the |
| 528 | contents of the file. This is better than simply deleting the buffer |
| 529 | contents and inserting the whole file, because (1) it preserves some |
| 530 | marker positions and (2) it puts less data in the undo list. |
| 531 | |
| 532 | It is possible to read a special file (such as a FIFO or an I/O device) |
| 533 | with @code{insert-file-contents}, as long as @var{replace} and |
| 534 | @var{visit} are @code{nil}. |
| 535 | @end defun |
| 536 | |
| 537 | @defun insert-file-contents-literally filename &optional visit beg end replace |
| 538 | This function works like @code{insert-file-contents} except that it does |
| 539 | not do format decoding (@pxref{Format Conversion}), does not do |
| 540 | character code conversion (@pxref{Coding Systems}), does not run |
| 541 | @code{find-file-hook}, does not perform automatic uncompression, and so |
| 542 | on. |
| 543 | @end defun |
| 544 | |
| 545 | If you want to pass a file name to another process so that another |
| 546 | program can read the file, use the function @code{file-local-copy}; see |
| 547 | @ref{Magic File Names}. |
| 548 | |
| 549 | @node Writing to Files |
| 550 | @comment node-name, next, previous, up |
| 551 | @section Writing to Files |
| 552 | @cindex writing to files |
| 553 | |
| 554 | You can write the contents of a buffer, or part of a buffer, directly |
| 555 | to a file on disk using the @code{append-to-file} and |
| 556 | @code{write-region} functions. Don't use these functions to write to |
| 557 | files that are being visited; that could cause confusion in the |
| 558 | mechanisms for visiting. |
| 559 | |
| 560 | @deffn Command append-to-file start end filename |
| 561 | This function appends the contents of the region delimited by |
| 562 | @var{start} and @var{end} in the current buffer to the end of file |
| 563 | @var{filename}. If that file does not exist, it is created. This |
| 564 | function returns @code{nil}. |
| 565 | |
| 566 | An error is signaled if @var{filename} specifies a nonwritable file, |
| 567 | or a nonexistent file in a directory where files cannot be created. |
| 568 | |
| 569 | When called from Lisp, this function is completely equivalent to: |
| 570 | |
| 571 | @example |
| 572 | (write-region start end filename t) |
| 573 | @end example |
| 574 | @end deffn |
| 575 | |
| 576 | @deffn Command write-region start end filename &optional append visit lockname mustbenew |
| 577 | This function writes the region delimited by @var{start} and @var{end} |
| 578 | in the current buffer into the file specified by @var{filename}. |
| 579 | |
| 580 | If @var{start} is @code{nil}, then the command writes the entire buffer |
| 581 | contents (@emph{not} just the accessible portion) to the file and |
| 582 | ignores @var{end}. |
| 583 | |
| 584 | @c Emacs 19 feature |
| 585 | If @var{start} is a string, then @code{write-region} writes or appends |
| 586 | that string, rather than text from the buffer. @var{end} is ignored in |
| 587 | this case. |
| 588 | |
| 589 | If @var{append} is non-@code{nil}, then the specified text is appended |
| 590 | to the existing file contents (if any). If @var{append} is an |
| 591 | integer, @code{write-region} seeks to that byte offset from the start |
| 592 | of the file and writes the data from there. |
| 593 | |
| 594 | If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks |
| 595 | for confirmation if @var{filename} names an existing file. If |
| 596 | @var{mustbenew} is the symbol @code{excl}, then @code{write-region} |
| 597 | does not ask for confirmation, but instead it signals an error |
| 598 | @code{file-already-exists} if the file already exists. |
| 599 | |
| 600 | The test for an existing file, when @var{mustbenew} is @code{excl}, uses |
| 601 | a special system feature. At least for files on a local disk, there is |
| 602 | no chance that some other program could create a file of the same name |
| 603 | before Emacs does, without Emacs's noticing. |
| 604 | |
| 605 | If @var{visit} is @code{t}, then Emacs establishes an association |
| 606 | between the buffer and the file: the buffer is then visiting that file. |
| 607 | It also sets the last file modification time for the current buffer to |
| 608 | @var{filename}'s modtime, and marks the buffer as not modified. This |
| 609 | feature is used by @code{save-buffer}, but you probably should not use |
| 610 | it yourself. |
| 611 | |
| 612 | @c Emacs 19 feature |
| 613 | If @var{visit} is a string, it specifies the file name to visit. This |
| 614 | way, you can write the data to one file (@var{filename}) while recording |
| 615 | the buffer as visiting another file (@var{visit}). The argument |
| 616 | @var{visit} is used in the echo area message and also for file locking; |
| 617 | @var{visit} is stored in @code{buffer-file-name}. This feature is used |
| 618 | to implement @code{file-precious-flag}; don't use it yourself unless you |
| 619 | really know what you're doing. |
| 620 | |
| 621 | The optional argument @var{lockname}, if non-@code{nil}, specifies the |
| 622 | file name to use for purposes of locking and unlocking, overriding |
| 623 | @var{filename} and @var{visit} for that purpose. |
| 624 | |
| 625 | The function @code{write-region} converts the data which it writes to |
| 626 | the appropriate file formats specified by @code{buffer-file-format} |
| 627 | and also calls the functions in the list |
| 628 | @code{write-region-annotate-functions}. |
| 629 | @xref{Format Conversion}. |
| 630 | |
| 631 | Normally, @code{write-region} displays the message @samp{Wrote |
| 632 | @var{filename}} in the echo area. If @var{visit} is neither @code{t} |
| 633 | nor @code{nil} nor a string, then this message is inhibited. This |
| 634 | feature is useful for programs that use files for internal purposes, |
| 635 | files that the user does not need to know about. |
| 636 | @end deffn |
| 637 | |
| 638 | @defmac with-temp-file file body@dots{} |
| 639 | @anchor{Definition of with-temp-file} |
| 640 | The @code{with-temp-file} macro evaluates the @var{body} forms with a |
| 641 | temporary buffer as the current buffer; then, at the end, it writes the |
| 642 | buffer contents into file @var{file}. It kills the temporary buffer |
| 643 | when finished, restoring the buffer that was current before the |
| 644 | @code{with-temp-file} form. Then it returns the value of the last form |
| 645 | in @var{body}. |
| 646 | |
| 647 | The current buffer is restored even in case of an abnormal exit via |
| 648 | @code{throw} or error (@pxref{Nonlocal Exits}). |
| 649 | |
| 650 | See also @code{with-temp-buffer} in @ref{Definition of |
| 651 | with-temp-buffer,, The Current Buffer}. |
| 652 | @end defmac |
| 653 | |
| 654 | @node File Locks |
| 655 | @section File Locks |
| 656 | @cindex file locks |
| 657 | @cindex lock file |
| 658 | |
| 659 | When two users edit the same file at the same time, they are likely |
| 660 | to interfere with each other. Emacs tries to prevent this situation |
| 661 | from arising by recording a @dfn{file lock} when a file is being |
| 662 | modified. (File locks are not implemented on Microsoft systems.) |
| 663 | Emacs can then detect the first attempt to modify a buffer visiting a |
| 664 | file that is locked by another Emacs job, and ask the user what to do. |
| 665 | The file lock is really a file, a symbolic link with a special name, |
| 666 | stored in the same directory as the file you are editing. |
| 667 | |
| 668 | When you access files using NFS, there may be a small probability that |
| 669 | you and another user will both lock the same file ``simultaneously.'' |
| 670 | If this happens, it is possible for the two users to make changes |
| 671 | simultaneously, but Emacs will still warn the user who saves second. |
| 672 | Also, the detection of modification of a buffer visiting a file changed |
| 673 | on disk catches some cases of simultaneous editing; see |
| 674 | @ref{Modification Time}. |
| 675 | |
| 676 | @defun file-locked-p filename |
| 677 | This function returns @code{nil} if the file @var{filename} is not |
| 678 | locked. It returns @code{t} if it is locked by this Emacs process, and |
| 679 | it returns the name of the user who has locked it if it is locked by |
| 680 | some other job. |
| 681 | |
| 682 | @example |
| 683 | @group |
| 684 | (file-locked-p "foo") |
| 685 | @result{} nil |
| 686 | @end group |
| 687 | @end example |
| 688 | @end defun |
| 689 | |
| 690 | @defun lock-buffer &optional filename |
| 691 | This function locks the file @var{filename}, if the current buffer is |
| 692 | modified. The argument @var{filename} defaults to the current buffer's |
| 693 | visited file. Nothing is done if the current buffer is not visiting a |
| 694 | file, or is not modified, or if the system does not support locking. |
| 695 | @end defun |
| 696 | |
| 697 | @defun unlock-buffer |
| 698 | This function unlocks the file being visited in the current buffer, |
| 699 | if the buffer is modified. If the buffer is not modified, then |
| 700 | the file should not be locked, so this function does nothing. It also |
| 701 | does nothing if the current buffer is not visiting a file, or if the |
| 702 | system does not support locking. |
| 703 | @end defun |
| 704 | |
| 705 | File locking is not supported on some systems. On systems that do not |
| 706 | support it, the functions @code{lock-buffer}, @code{unlock-buffer} and |
| 707 | @code{file-locked-p} do nothing and return @code{nil}. |
| 708 | |
| 709 | @defun ask-user-about-lock file other-user |
| 710 | This function is called when the user tries to modify @var{file}, but it |
| 711 | is locked by another user named @var{other-user}. The default |
| 712 | definition of this function asks the user to say what to do. The value |
| 713 | this function returns determines what Emacs does next: |
| 714 | |
| 715 | @itemize @bullet |
| 716 | @item |
| 717 | A value of @code{t} says to grab the lock on the file. Then |
| 718 | this user may edit the file and @var{other-user} loses the lock. |
| 719 | |
| 720 | @item |
| 721 | A value of @code{nil} says to ignore the lock and let this |
| 722 | user edit the file anyway. |
| 723 | |
| 724 | @item |
| 725 | @kindex file-locked |
| 726 | This function may instead signal a @code{file-locked} error, in which |
| 727 | case the change that the user was about to make does not take place. |
| 728 | |
| 729 | The error message for this error looks like this: |
| 730 | |
| 731 | @example |
| 732 | @error{} File is locked: @var{file} @var{other-user} |
| 733 | @end example |
| 734 | |
| 735 | @noindent |
| 736 | where @code{file} is the name of the file and @var{other-user} is the |
| 737 | name of the user who has locked the file. |
| 738 | @end itemize |
| 739 | |
| 740 | If you wish, you can replace the @code{ask-user-about-lock} function |
| 741 | with your own version that makes the decision in another way. The code |
| 742 | for its usual definition is in @file{userlock.el}. |
| 743 | @end defun |
| 744 | |
| 745 | @node Information about Files |
| 746 | @section Information about Files |
| 747 | @cindex file, information about |
| 748 | |
| 749 | The functions described in this section all operate on strings that |
| 750 | designate file names. With a few exceptions, all the functions have |
| 751 | names that begin with the word @samp{file}. These functions all |
| 752 | return information about actual files or directories, so their |
| 753 | arguments must all exist as actual files or directories unless |
| 754 | otherwise noted. |
| 755 | |
| 756 | @menu |
| 757 | * Testing Accessibility:: Is a given file readable? Writable? |
| 758 | * Kinds of Files:: Is it a directory? A symbolic link? |
| 759 | * Truenames:: Eliminating symbolic links from a file name. |
| 760 | * File Attributes:: How large is it? Any other names? Etc. |
| 761 | * Locating Files:: How to find a file in standard places. |
| 762 | @end menu |
| 763 | |
| 764 | @node Testing Accessibility |
| 765 | @comment node-name, next, previous, up |
| 766 | @subsection Testing Accessibility |
| 767 | @cindex accessibility of a file |
| 768 | @cindex file accessibility |
| 769 | |
| 770 | These functions test for permission to access a file in specific |
| 771 | ways. Unless explicitly stated otherwise, they recursively follow |
| 772 | symbolic links for their file name arguments, at all levels (at the |
| 773 | level of the file itself and at all levels of parent directories). |
| 774 | |
| 775 | @defun file-exists-p filename |
| 776 | This function returns @code{t} if a file named @var{filename} appears |
| 777 | to exist. This does not mean you can necessarily read the file, only |
| 778 | that you can find out its attributes. (On Unix and GNU/Linux, this is |
| 779 | true if the file exists and you have execute permission on the |
| 780 | containing directories, regardless of the protection of the file |
| 781 | itself.) |
| 782 | |
| 783 | If the file does not exist, or if fascist access control policies |
| 784 | prevent you from finding the attributes of the file, this function |
| 785 | returns @code{nil}. |
| 786 | |
| 787 | Directories are files, so @code{file-exists-p} returns @code{t} when |
| 788 | given a directory name. However, symbolic links are treated |
| 789 | specially; @code{file-exists-p} returns @code{t} for a symbolic link |
| 790 | name only if the target file exists. |
| 791 | @end defun |
| 792 | |
| 793 | @defun file-readable-p filename |
| 794 | This function returns @code{t} if a file named @var{filename} exists |
| 795 | and you can read it. It returns @code{nil} otherwise. |
| 796 | |
| 797 | @example |
| 798 | @group |
| 799 | (file-readable-p "files.texi") |
| 800 | @result{} t |
| 801 | @end group |
| 802 | @group |
| 803 | (file-exists-p "/usr/spool/mqueue") |
| 804 | @result{} t |
| 805 | @end group |
| 806 | @group |
| 807 | (file-readable-p "/usr/spool/mqueue") |
| 808 | @result{} nil |
| 809 | @end group |
| 810 | @end example |
| 811 | @end defun |
| 812 | |
| 813 | @c Emacs 19 feature |
| 814 | @defun file-executable-p filename |
| 815 | This function returns @code{t} if a file named @var{filename} exists and |
| 816 | you can execute it. It returns @code{nil} otherwise. On Unix and |
| 817 | GNU/Linux, if the file is a directory, execute permission means you can |
| 818 | check the existence and attributes of files inside the directory, and |
| 819 | open those files if their modes permit. |
| 820 | @end defun |
| 821 | |
| 822 | @defun file-writable-p filename |
| 823 | This function returns @code{t} if the file @var{filename} can be written |
| 824 | or created by you, and @code{nil} otherwise. A file is writable if the |
| 825 | file exists and you can write it. It is creatable if it does not exist, |
| 826 | but the specified directory does exist and you can write in that |
| 827 | directory. |
| 828 | |
| 829 | In the third example below, @file{foo} is not writable because the |
| 830 | parent directory does not exist, even though the user could create such |
| 831 | a directory. |
| 832 | |
| 833 | @example |
| 834 | @group |
| 835 | (file-writable-p "~/foo") |
| 836 | @result{} t |
| 837 | @end group |
| 838 | @group |
| 839 | (file-writable-p "/foo") |
| 840 | @result{} nil |
| 841 | @end group |
| 842 | @group |
| 843 | (file-writable-p "~/no-such-dir/foo") |
| 844 | @result{} nil |
| 845 | @end group |
| 846 | @end example |
| 847 | @end defun |
| 848 | |
| 849 | @c Emacs 19 feature |
| 850 | @defun file-accessible-directory-p dirname |
| 851 | This function returns @code{t} if you have permission to open existing |
| 852 | files in the directory whose name as a file is @var{dirname}; |
| 853 | otherwise (or if there is no such directory), it returns @code{nil}. |
| 854 | The value of @var{dirname} may be either a directory name (such as |
| 855 | @file{/foo/}) or the file name of a file which is a directory |
| 856 | (such as @file{/foo}, without the final slash). |
| 857 | |
| 858 | Example: after the following, |
| 859 | |
| 860 | @example |
| 861 | (file-accessible-directory-p "/foo") |
| 862 | @result{} nil |
| 863 | @end example |
| 864 | |
| 865 | @noindent |
| 866 | we can deduce that any attempt to read a file in @file{/foo/} will |
| 867 | give an error. |
| 868 | @end defun |
| 869 | |
| 870 | @defun access-file filename string |
| 871 | This function opens file @var{filename} for reading, then closes it and |
| 872 | returns @code{nil}. However, if the open fails, it signals an error |
| 873 | using @var{string} as the error message text. |
| 874 | @end defun |
| 875 | |
| 876 | @defun file-ownership-preserved-p filename |
| 877 | This function returns @code{t} if deleting the file @var{filename} and |
| 878 | then creating it anew would keep the file's owner unchanged. It also |
| 879 | returns @code{t} for nonexistent files. |
| 880 | |
| 881 | If @var{filename} is a symbolic link, then, unlike the other functions |
| 882 | discussed here, @code{file-ownership-preserved-p} does @emph{not} |
| 883 | replace @var{filename} with its target. However, it does recursively |
| 884 | follow symbolic links at all levels of parent directories. |
| 885 | @end defun |
| 886 | |
| 887 | @defun file-newer-than-file-p filename1 filename2 |
| 888 | @cindex file age |
| 889 | @cindex file modification time |
| 890 | This function returns @code{t} if the file @var{filename1} is |
| 891 | newer than file @var{filename2}. If @var{filename1} does not |
| 892 | exist, it returns @code{nil}. If @var{filename1} does exist, but |
| 893 | @var{filename2} does not, it returns @code{t}. |
| 894 | |
| 895 | In the following example, assume that the file @file{aug-19} was written |
| 896 | on the 19th, @file{aug-20} was written on the 20th, and the file |
| 897 | @file{no-file} doesn't exist at all. |
| 898 | |
| 899 | @example |
| 900 | @group |
| 901 | (file-newer-than-file-p "aug-19" "aug-20") |
| 902 | @result{} nil |
| 903 | @end group |
| 904 | @group |
| 905 | (file-newer-than-file-p "aug-20" "aug-19") |
| 906 | @result{} t |
| 907 | @end group |
| 908 | @group |
| 909 | (file-newer-than-file-p "aug-19" "no-file") |
| 910 | @result{} t |
| 911 | @end group |
| 912 | @group |
| 913 | (file-newer-than-file-p "no-file" "aug-19") |
| 914 | @result{} nil |
| 915 | @end group |
| 916 | @end example |
| 917 | |
| 918 | You can use @code{file-attributes} to get a file's last modification |
| 919 | time as a list of two numbers. @xref{File Attributes}. |
| 920 | @end defun |
| 921 | |
| 922 | @node Kinds of Files |
| 923 | @comment node-name, next, previous, up |
| 924 | @subsection Distinguishing Kinds of Files |
| 925 | |
| 926 | This section describes how to distinguish various kinds of files, such |
| 927 | as directories, symbolic links, and ordinary files. |
| 928 | |
| 929 | @defun file-symlink-p filename |
| 930 | @cindex file symbolic links |
| 931 | If the file @var{filename} is a symbolic link, the |
| 932 | @code{file-symlink-p} function returns the (non-recursive) link target |
| 933 | as a string. (Determining the file name that the link points to from |
| 934 | the target is nontrivial.) First, this function recursively follows |
| 935 | symbolic links at all levels of parent directories. |
| 936 | |
| 937 | If the file @var{filename} is not a symbolic link (or there is no such file), |
| 938 | @code{file-symlink-p} returns @code{nil}. |
| 939 | |
| 940 | @example |
| 941 | @group |
| 942 | (file-symlink-p "foo") |
| 943 | @result{} nil |
| 944 | @end group |
| 945 | @group |
| 946 | (file-symlink-p "sym-link") |
| 947 | @result{} "foo" |
| 948 | @end group |
| 949 | @group |
| 950 | (file-symlink-p "sym-link2") |
| 951 | @result{} "sym-link" |
| 952 | @end group |
| 953 | @group |
| 954 | (file-symlink-p "/bin") |
| 955 | @result{} "/pub/bin" |
| 956 | @end group |
| 957 | @end example |
| 958 | |
| 959 | @c !!! file-symlink-p: should show output of ls -l for comparison |
| 960 | @end defun |
| 961 | |
| 962 | The next two functions recursively follow symbolic links at |
| 963 | all levels for @var{filename}. |
| 964 | |
| 965 | @defun file-directory-p filename |
| 966 | This function returns @code{t} if @var{filename} is the name of an |
| 967 | existing directory, @code{nil} otherwise. |
| 968 | |
| 969 | @example |
| 970 | @group |
| 971 | (file-directory-p "~rms") |
| 972 | @result{} t |
| 973 | @end group |
| 974 | @group |
| 975 | (file-directory-p "~rms/lewis/files.texi") |
| 976 | @result{} nil |
| 977 | @end group |
| 978 | @group |
| 979 | (file-directory-p "~rms/lewis/no-such-file") |
| 980 | @result{} nil |
| 981 | @end group |
| 982 | @group |
| 983 | (file-directory-p "$HOME") |
| 984 | @result{} nil |
| 985 | @end group |
| 986 | @group |
| 987 | (file-directory-p |
| 988 | (substitute-in-file-name "$HOME")) |
| 989 | @result{} t |
| 990 | @end group |
| 991 | @end example |
| 992 | @end defun |
| 993 | |
| 994 | @defun file-regular-p filename |
| 995 | This function returns @code{t} if the file @var{filename} exists and is |
| 996 | a regular file (not a directory, named pipe, terminal, or |
| 997 | other I/O device). |
| 998 | @end defun |
| 999 | |
| 1000 | @node Truenames |
| 1001 | @subsection Truenames |
| 1002 | @cindex truename (of file) |
| 1003 | |
| 1004 | @c Emacs 19 features |
| 1005 | The @dfn{truename} of a file is the name that you get by following |
| 1006 | symbolic links at all levels until none remain, then simplifying away |
| 1007 | @samp{.}@: and @samp{..}@: appearing as name components. This results |
| 1008 | in a sort of canonical name for the file. A file does not always have a |
| 1009 | unique truename; the number of distinct truenames a file has is equal to |
| 1010 | the number of hard links to the file. However, truenames are useful |
| 1011 | because they eliminate symbolic links as a cause of name variation. |
| 1012 | |
| 1013 | @defun file-truename filename |
| 1014 | The function @code{file-truename} returns the truename of the file |
| 1015 | @var{filename}. The argument must be an absolute file name. |
| 1016 | |
| 1017 | This function does not expand environment variables. Only |
| 1018 | @code{substitute-in-file-name} does that. @xref{Definition of |
| 1019 | substitute-in-file-name}. |
| 1020 | |
| 1021 | If you may need to follow symbolic links preceding @samp{..}@: |
| 1022 | appearing as a name component, you should make sure to call |
| 1023 | @code{file-truename} without prior direct or indirect calls to |
| 1024 | @code{expand-file-name}, as otherwise the file name component |
| 1025 | immediately preceding @samp{..} will be ``simplified away'' before |
| 1026 | @code{file-truename} is called. To eliminate the need for a call to |
| 1027 | @code{expand-file-name}, @code{file-truename} handles @samp{~} in the |
| 1028 | same way that @code{expand-file-name} does. @xref{File Name |
| 1029 | Expansion,, Functions that Expand Filenames}. |
| 1030 | @end defun |
| 1031 | |
| 1032 | @defun file-chase-links filename &optional limit |
| 1033 | This function follows symbolic links, starting with @var{filename}, |
| 1034 | until it finds a file name which is not the name of a symbolic link. |
| 1035 | Then it returns that file name. This function does @emph{not} follow |
| 1036 | symbolic links at the level of parent directories. |
| 1037 | |
| 1038 | If you specify a number for @var{limit}, then after chasing through |
| 1039 | that many links, the function just returns what it has even if that is |
| 1040 | still a symbolic link. |
| 1041 | @end defun |
| 1042 | |
| 1043 | To illustrate the difference between @code{file-chase-links} and |
| 1044 | @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to |
| 1045 | the directory @file{/home/foo}, and @file{/home/foo/hello} is an |
| 1046 | ordinary file (or at least, not a symbolic link) or nonexistent. Then |
| 1047 | we would have: |
| 1048 | |
| 1049 | @example |
| 1050 | (file-chase-links "/usr/foo/hello") |
| 1051 | ;; @r{This does not follow the links in the parent directories.} |
| 1052 | @result{} "/usr/foo/hello" |
| 1053 | (file-truename "/usr/foo/hello") |
| 1054 | ;; @r{Assuming that @file{/home} is not a symbolic link.} |
| 1055 | @result{} "/home/foo/hello" |
| 1056 | @end example |
| 1057 | |
| 1058 | @xref{Buffer File Name}, for related information. |
| 1059 | |
| 1060 | @node File Attributes |
| 1061 | @comment node-name, next, previous, up |
| 1062 | @subsection Other Information about Files |
| 1063 | |
| 1064 | This section describes the functions for getting detailed information |
| 1065 | about a file, other than its contents. This information includes the |
| 1066 | mode bits that control access permission, the owner and group numbers, |
| 1067 | the number of names, the inode number, the size, and the times of access |
| 1068 | and modification. |
| 1069 | |
| 1070 | @defun file-modes filename |
| 1071 | @cindex permission |
| 1072 | @cindex file attributes |
| 1073 | This function returns the mode bits of @var{filename}, as an integer. |
| 1074 | The mode bits are also called the file permissions, and they specify |
| 1075 | access control in the usual Unix fashion. If the low-order bit is 1, |
| 1076 | then the file is executable by all users, if the second-lowest-order bit |
| 1077 | is 1, then the file is writable by all users, etc. |
| 1078 | |
| 1079 | The highest value returnable is 4095 (7777 octal), meaning that |
| 1080 | everyone has read, write, and execute permission, that the @acronym{SUID} bit |
| 1081 | is set for both others and group, and that the sticky bit is set. |
| 1082 | |
| 1083 | If @var{filename} does not exist, @code{file-modes} returns @code{nil}. |
| 1084 | |
| 1085 | This function recursively follows symbolic links at all levels. |
| 1086 | |
| 1087 | @example |
| 1088 | @group |
| 1089 | (file-modes "~/junk/diffs") |
| 1090 | @result{} 492 ; @r{Decimal integer.} |
| 1091 | @end group |
| 1092 | @group |
| 1093 | (format "%o" 492) |
| 1094 | @result{} "754" ; @r{Convert to octal.} |
| 1095 | @end group |
| 1096 | |
| 1097 | @group |
| 1098 | (set-file-modes "~/junk/diffs" 438) |
| 1099 | @result{} nil |
| 1100 | @end group |
| 1101 | |
| 1102 | @group |
| 1103 | (format "%o" 438) |
| 1104 | @result{} "666" ; @r{Convert to octal.} |
| 1105 | @end group |
| 1106 | |
| 1107 | @group |
| 1108 | % ls -l diffs |
| 1109 | -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs |
| 1110 | @end group |
| 1111 | @end example |
| 1112 | @end defun |
| 1113 | |
| 1114 | If the @var{filename} argument to the next two functions is a symbolic |
| 1115 | link, then these function do @emph{not} replace it with its target. |
| 1116 | However, they both recursively follow symbolic links at all levels of |
| 1117 | parent directories. |
| 1118 | |
| 1119 | @defun file-nlinks filename |
| 1120 | This functions returns the number of names (i.e., hard links) that |
| 1121 | file @var{filename} has. If the file does not exist, then this function |
| 1122 | returns @code{nil}. Note that symbolic links have no effect on this |
| 1123 | function, because they are not considered to be names of the files they |
| 1124 | link to. |
| 1125 | |
| 1126 | @example |
| 1127 | @group |
| 1128 | % ls -l foo* |
| 1129 | -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo |
| 1130 | -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 |
| 1131 | @end group |
| 1132 | |
| 1133 | @group |
| 1134 | (file-nlinks "foo") |
| 1135 | @result{} 2 |
| 1136 | @end group |
| 1137 | @group |
| 1138 | (file-nlinks "doesnt-exist") |
| 1139 | @result{} nil |
| 1140 | @end group |
| 1141 | @end example |
| 1142 | @end defun |
| 1143 | |
| 1144 | @defun file-attributes filename &optional id-format |
| 1145 | @anchor{Definition of file-attributes} |
| 1146 | This function returns a list of attributes of file @var{filename}. If |
| 1147 | the specified file cannot be opened, it returns @code{nil}. |
| 1148 | The optional parameter @var{id-format} specifies the preferred format |
| 1149 | of attributes @acronym{UID} and @acronym{GID} (see below)---the |
| 1150 | valid values are @code{'string} and @code{'integer}. The latter is |
| 1151 | the default, but we plan to change that, so you should specify a |
| 1152 | non-@code{nil} value for @var{id-format} if you use the returned |
| 1153 | @acronym{UID} or @acronym{GID}. |
| 1154 | |
| 1155 | The elements of the list, in order, are: |
| 1156 | |
| 1157 | @enumerate 0 |
| 1158 | @item |
| 1159 | @code{t} for a directory, a string for a symbolic link (the name |
| 1160 | linked to), or @code{nil} for a text file. |
| 1161 | |
| 1162 | @c Wordy so as to prevent an overfull hbox. --rjc 15mar92 |
| 1163 | @item |
| 1164 | The number of names the file has. Alternate names, also known as hard |
| 1165 | links, can be created by using the @code{add-name-to-file} function |
| 1166 | (@pxref{Changing Files}). |
| 1167 | |
| 1168 | @item |
| 1169 | The file's @acronym{UID}, normally as a string. However, if it does |
| 1170 | not correspond to a named user, the value is an integer or a floating |
| 1171 | point number. |
| 1172 | |
| 1173 | @item |
| 1174 | The file's @acronym{GID}, likewise. |
| 1175 | |
| 1176 | @item |
| 1177 | The time of last access, as a list of two integers. |
| 1178 | The first integer has the high-order 16 bits of time, |
| 1179 | the second has the low 16 bits. (This is similar to the |
| 1180 | value of @code{current-time}; see @ref{Time of Day}.) Note that on |
| 1181 | some FAT-based filesystems, only the date of last access is recorded, |
| 1182 | so this time will always hold the midnight of the day of last access. |
| 1183 | |
| 1184 | @cindex modification time of file |
| 1185 | @item |
| 1186 | The time of last modification as a list of two integers (as above). |
| 1187 | This is the last time when the file's contents were modified. |
| 1188 | |
| 1189 | @item |
| 1190 | The time of last status change as a list of two integers (as above). |
| 1191 | This is the time of the last change to the file's access mode bits, |
| 1192 | its owner and group, and other information recorded in the filesystem |
| 1193 | for the file, beyond the file's contents. |
| 1194 | |
| 1195 | @item |
| 1196 | The size of the file in bytes. If the size is too large to fit in a |
| 1197 | Lisp integer, this is a floating point number. |
| 1198 | |
| 1199 | @item |
| 1200 | The file's modes, as a string of ten letters or dashes, |
| 1201 | as in @samp{ls -l}. |
| 1202 | |
| 1203 | @item |
| 1204 | @code{t} if the file's @acronym{GID} would change if file were |
| 1205 | deleted and recreated; @code{nil} otherwise. |
| 1206 | |
| 1207 | @item |
| 1208 | The file's inode number. If possible, this is an integer. If the |
| 1209 | inode number is too large to be represented as an integer in Emacs |
| 1210 | Lisp, but still fits into a 32-bit integer, then the value has the |
| 1211 | form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16 |
| 1212 | bits. If the inode is wider than 32 bits, the value is of the form |
| 1213 | @code{(@var{high} @var{middle} . @var{low})}, where @code{high} holds |
| 1214 | the high 24 bits, @var{middle} the next 24 bits, and @var{low} the low |
| 1215 | 16 bits. |
| 1216 | |
| 1217 | @item |
| 1218 | The filesystem number of the device that the file is on. Depending on |
| 1219 | the magnitude of the value, this can be either an integer or a cons |
| 1220 | cell, in the same manner as the inode number. This element and the |
| 1221 | file's inode number together give enough information to distinguish |
| 1222 | any two files on the system---no two files can have the same values |
| 1223 | for both of these numbers. |
| 1224 | @end enumerate |
| 1225 | |
| 1226 | For example, here are the file attributes for @file{files.texi}: |
| 1227 | |
| 1228 | @example |
| 1229 | @group |
| 1230 | (file-attributes "files.texi" 'string) |
| 1231 | @result{} (nil 1 "lh" "users" |
| 1232 | (19145 42977) |
| 1233 | (19141 59576) |
| 1234 | (18340 17300) |
| 1235 | 122295 "-rw-rw-rw-" |
| 1236 | nil (5888 2 . 43978) |
| 1237 | (15479 . 46724)) |
| 1238 | @end group |
| 1239 | @end example |
| 1240 | |
| 1241 | @noindent |
| 1242 | and here is how the result is interpreted: |
| 1243 | |
| 1244 | @table @code |
| 1245 | @item nil |
| 1246 | is neither a directory nor a symbolic link. |
| 1247 | |
| 1248 | @item 1 |
| 1249 | has only one name (the name @file{files.texi} in the current default |
| 1250 | directory). |
| 1251 | |
| 1252 | @item "lh" |
| 1253 | is owned by the user with name "lh". |
| 1254 | |
| 1255 | @item "users" |
| 1256 | is in the group with name "users". |
| 1257 | |
| 1258 | @item (19145 42977) |
| 1259 | was last accessed on Oct 5 2009, at 10:01:37. |
| 1260 | |
| 1261 | @item (19141 59576) |
| 1262 | last had its contents modified on Oct 2 2009, at 13:49:12. |
| 1263 | |
| 1264 | @item (18340 17300) |
| 1265 | last had its status changed on Feb 2 2008, at 12:19:00. |
| 1266 | |
| 1267 | @item 122295 |
| 1268 | is 122295 bytes long. (It may not contain 122295 characters, though, |
| 1269 | if some of the bytes belong to multibyte sequences, and also if the |
| 1270 | end-of-line format is CR-LF.) |
| 1271 | |
| 1272 | @item "-rw-rw-rw-" |
| 1273 | has a mode of read and write access for the owner, group, and world. |
| 1274 | |
| 1275 | @item nil |
| 1276 | would retain the same @acronym{GID} if it were recreated. |
| 1277 | |
| 1278 | @item (5888 2 . 43978) |
| 1279 | has an inode number of 6473924464520138. |
| 1280 | |
| 1281 | @item (15479 . 46724) |
| 1282 | is on the file-system device whose number is 1014478468. |
| 1283 | @end table |
| 1284 | @end defun |
| 1285 | |
| 1286 | @cindex MS-DOS and file modes |
| 1287 | @cindex file modes and MS-DOS |
| 1288 | On MS-DOS, there is no such thing as an ``executable'' file mode bit. |
| 1289 | So Emacs considers a file executable if its name ends in one of the |
| 1290 | standard executable extensions, such as @file{.com}, @file{.bat}, |
| 1291 | @file{.exe}, and some others. Files that begin with the Unix-standard |
| 1292 | @samp{#!} signature, such as shell and Perl scripts, are also considered |
| 1293 | as executable files. This is reflected in the values returned by |
| 1294 | @code{file-modes} and @code{file-attributes}. Directories are also |
| 1295 | reported with executable bit set, for compatibility with Unix. |
| 1296 | |
| 1297 | @node Locating Files |
| 1298 | @subsection How to Locate Files in Standard Places |
| 1299 | @cindex locate file in path |
| 1300 | @cindex find file in path |
| 1301 | |
| 1302 | This section explains how to search for a file in a list of |
| 1303 | directories (a @dfn{path}). One example is when you need to look for |
| 1304 | a program's executable file, e.g., to find out whether a given program |
| 1305 | is installed on the user's system. Another example is the search for |
| 1306 | Lisp libraries (@pxref{Library Search}). Such searches generally need |
| 1307 | to try various possible file name extensions, in addition to various |
| 1308 | possible directories. Emacs provides a function for such a |
| 1309 | generalized search for a file. |
| 1310 | |
| 1311 | @defun locate-file filename path &optional suffixes predicate |
| 1312 | This function searches for a file whose name is @var{filename} in a |
| 1313 | list of directories given by @var{path}, trying the suffixes in |
| 1314 | @var{suffixes}. If it finds such a file, it returns the full |
| 1315 | @dfn{absolute file name} of the file (@pxref{Relative File Names}); |
| 1316 | otherwise it returns @code{nil}. |
| 1317 | |
| 1318 | The optional argument @var{suffixes} gives the list of file-name |
| 1319 | suffixes to append to @var{filename} when searching. |
| 1320 | @code{locate-file} tries each possible directory with each of these |
| 1321 | suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there |
| 1322 | are no suffixes, and @var{filename} is used only as-is. Typical |
| 1323 | values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess |
| 1324 | Creation, exec-suffixes}), @code{load-suffixes}, |
| 1325 | @code{load-file-rep-suffixes} and the return value of the function |
| 1326 | @code{get-load-suffixes} (@pxref{Load Suffixes}). |
| 1327 | |
| 1328 | Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess |
| 1329 | Creation, exec-path}) when looking for executable programs or |
| 1330 | @code{load-path} (@pxref{Library Search, load-path}) when looking for |
| 1331 | Lisp files. If @var{filename} is absolute, @var{path} has no effect, |
| 1332 | but the suffixes in @var{suffixes} are still tried. |
| 1333 | |
| 1334 | The optional argument @var{predicate}, if non-@code{nil}, specifies |
| 1335 | the predicate function to use for testing whether a candidate file is |
| 1336 | suitable. The predicate function is passed the candidate file name as |
| 1337 | its single argument. If @var{predicate} is @code{nil} or unspecified, |
| 1338 | @code{locate-file} uses @code{file-readable-p} as the default |
| 1339 | predicate. Useful non-default predicates include |
| 1340 | @code{file-executable-p}, @code{file-directory-p}, and other |
| 1341 | predicates described in @ref{Kinds of Files}. |
| 1342 | |
| 1343 | For compatibility, @var{predicate} can also be one of the symbols |
| 1344 | @code{executable}, @code{readable}, @code{writable}, @code{exists}, or |
| 1345 | a list of one or more of these symbols. |
| 1346 | @end defun |
| 1347 | |
| 1348 | @defun executable-find program |
| 1349 | This function searches for the executable file of the named |
| 1350 | @var{program} and returns the full absolute name of the executable, |
| 1351 | including its file-name extensions, if any. It returns @code{nil} if |
| 1352 | the file is not found. The functions searches in all the directories |
| 1353 | in @code{exec-path} and tries all the file-name extensions in |
| 1354 | @code{exec-suffixes}. |
| 1355 | @end defun |
| 1356 | |
| 1357 | @node Changing Files |
| 1358 | @section Changing File Names and Attributes |
| 1359 | @c @cindex renaming files Duplicates rename-file |
| 1360 | @cindex copying files |
| 1361 | @cindex deleting files |
| 1362 | @cindex linking files |
| 1363 | @cindex setting modes of files |
| 1364 | |
| 1365 | The functions in this section rename, copy, delete, link, and set the |
| 1366 | modes of files. |
| 1367 | |
| 1368 | In the functions that have an argument @var{newname}, if a file by the |
| 1369 | name of @var{newname} already exists, the actions taken depend on the |
| 1370 | value of the argument @var{ok-if-already-exists}: |
| 1371 | |
| 1372 | @itemize @bullet |
| 1373 | @item |
| 1374 | Signal a @code{file-already-exists} error if |
| 1375 | @var{ok-if-already-exists} is @code{nil}. |
| 1376 | |
| 1377 | @item |
| 1378 | Request confirmation if @var{ok-if-already-exists} is a number. |
| 1379 | |
| 1380 | @item |
| 1381 | Replace the old file without confirmation if @var{ok-if-already-exists} |
| 1382 | is any other value. |
| 1383 | @end itemize |
| 1384 | |
| 1385 | The next four commands all recursively follow symbolic links at all |
| 1386 | levels of parent directories for their first argument, but, if that |
| 1387 | argument is itself a symbolic link, then only @code{copy-file} |
| 1388 | replaces it with its (recursive) target. |
| 1389 | |
| 1390 | @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists |
| 1391 | @cindex file with multiple names |
| 1392 | @cindex file hard link |
| 1393 | This function gives the file named @var{oldname} the additional name |
| 1394 | @var{newname}. This means that @var{newname} becomes a new ``hard |
| 1395 | link'' to @var{oldname}. |
| 1396 | |
| 1397 | In the first part of the following example, we list two files, |
| 1398 | @file{foo} and @file{foo3}. |
| 1399 | |
| 1400 | @example |
| 1401 | @group |
| 1402 | % ls -li fo* |
| 1403 | 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo |
| 1404 | 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 |
| 1405 | @end group |
| 1406 | @end example |
| 1407 | |
| 1408 | Now we create a hard link, by calling @code{add-name-to-file}, then list |
| 1409 | the files again. This shows two names for one file, @file{foo} and |
| 1410 | @file{foo2}. |
| 1411 | |
| 1412 | @example |
| 1413 | @group |
| 1414 | (add-name-to-file "foo" "foo2") |
| 1415 | @result{} nil |
| 1416 | @end group |
| 1417 | |
| 1418 | @group |
| 1419 | % ls -li fo* |
| 1420 | 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo |
| 1421 | 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 |
| 1422 | 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 |
| 1423 | @end group |
| 1424 | @end example |
| 1425 | |
| 1426 | Finally, we evaluate the following: |
| 1427 | |
| 1428 | @example |
| 1429 | (add-name-to-file "foo" "foo3" t) |
| 1430 | @end example |
| 1431 | |
| 1432 | @noindent |
| 1433 | and list the files again. Now there are three names |
| 1434 | for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old |
| 1435 | contents of @file{foo3} are lost. |
| 1436 | |
| 1437 | @example |
| 1438 | @group |
| 1439 | (add-name-to-file "foo1" "foo3") |
| 1440 | @result{} nil |
| 1441 | @end group |
| 1442 | |
| 1443 | @group |
| 1444 | % ls -li fo* |
| 1445 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo |
| 1446 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 |
| 1447 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3 |
| 1448 | @end group |
| 1449 | @end example |
| 1450 | |
| 1451 | This function is meaningless on operating systems where multiple names |
| 1452 | for one file are not allowed. Some systems implement multiple names |
| 1453 | by copying the file instead. |
| 1454 | |
| 1455 | See also @code{file-nlinks} in @ref{File Attributes}. |
| 1456 | @end deffn |
| 1457 | |
| 1458 | @deffn Command rename-file filename newname &optional ok-if-already-exists |
| 1459 | This command renames the file @var{filename} as @var{newname}. |
| 1460 | |
| 1461 | If @var{filename} has additional names aside from @var{filename}, it |
| 1462 | continues to have those names. In fact, adding the name @var{newname} |
| 1463 | with @code{add-name-to-file} and then deleting @var{filename} has the |
| 1464 | same effect as renaming, aside from momentary intermediate states. |
| 1465 | @end deffn |
| 1466 | |
| 1467 | @deffn Command copy-file oldname newname &optional ok-if-exists time preserve-uid-gid |
| 1468 | This command copies the file @var{oldname} to @var{newname}. An |
| 1469 | error is signaled if @var{oldname} does not exist. If @var{newname} |
| 1470 | names a directory, it copies @var{oldname} into that directory, |
| 1471 | preserving its final name component. |
| 1472 | |
| 1473 | If @var{time} is non-@code{nil}, then this function gives the new file |
| 1474 | the same last-modified time that the old one has. (This works on only |
| 1475 | some operating systems.) If setting the time gets an error, |
| 1476 | @code{copy-file} signals a @code{file-date-error} error. In an |
| 1477 | interactive call, a prefix argument specifies a non-@code{nil} value |
| 1478 | for @var{time}. |
| 1479 | |
| 1480 | This function copies the file modes, too. |
| 1481 | |
| 1482 | If argument @var{preserve-uid-gid} is @code{nil}, we let the operating |
| 1483 | system decide the user and group ownership of the new file (this is |
| 1484 | usually set to the user running Emacs). If @var{preserve-uid-gid} is |
| 1485 | non-@code{nil}, we attempt to copy the user and group ownership of the |
| 1486 | file. This works only on some operating systems, and only if you have |
| 1487 | the correct permissions to do so. |
| 1488 | @end deffn |
| 1489 | |
| 1490 | @deffn Command make-symbolic-link filename newname &optional ok-if-exists |
| 1491 | @pindex ln |
| 1492 | @kindex file-already-exists |
| 1493 | This command makes a symbolic link to @var{filename}, named |
| 1494 | @var{newname}. This is like the shell command @samp{ln -s |
| 1495 | @var{filename} @var{newname}}. |
| 1496 | |
| 1497 | This function is not available on systems that don't support symbolic |
| 1498 | links. |
| 1499 | @end deffn |
| 1500 | |
| 1501 | @deffn Command delete-file filename |
| 1502 | @pindex rm |
| 1503 | This command deletes the file @var{filename}, like the shell command |
| 1504 | @samp{rm @var{filename}}. If the file has multiple names, it continues |
| 1505 | to exist under the other names. |
| 1506 | |
| 1507 | A suitable kind of @code{file-error} error is signaled if the file does |
| 1508 | not exist, or is not deletable. (On Unix and GNU/Linux, a file is |
| 1509 | deletable if its directory is writable.) |
| 1510 | |
| 1511 | If @var{filename} is a symbolic link, @code{delete-file} does not |
| 1512 | replace it with its target, but it does follow symbolic links at all |
| 1513 | levels of parent directories. |
| 1514 | |
| 1515 | See also @code{delete-directory} in @ref{Create/Delete Dirs}. |
| 1516 | @end deffn |
| 1517 | |
| 1518 | @deffn Command set-file-modes filename mode |
| 1519 | This function sets mode bits of @var{filename} to @var{mode} (which |
| 1520 | must be an integer when the function is called non-interactively). |
| 1521 | Only the low 12 bits of @var{mode} are used. |
| 1522 | |
| 1523 | Interactively, @var{mode} is read from the minibuffer using |
| 1524 | @code{read-file-modes}, which accepts mode bits either as a number or |
| 1525 | as a character string representing the mode bits symbolically. See |
| 1526 | the description of @code{read-file-modes} below for the supported |
| 1527 | forms of symbolic notation for mode bits. |
| 1528 | |
| 1529 | This function recursively follows symbolic links at all levels for |
| 1530 | @var{filename}. |
| 1531 | @end deffn |
| 1532 | |
| 1533 | @c Emacs 19 feature |
| 1534 | @defun set-default-file-modes mode |
| 1535 | @cindex umask |
| 1536 | This function sets the default file protection for new files created by |
| 1537 | Emacs and its subprocesses. Every file created with Emacs initially has |
| 1538 | this protection, or a subset of it (@code{write-region} will not give a |
| 1539 | file execute permission even if the default file protection allows |
| 1540 | execute permission). On Unix and GNU/Linux, the default protection is |
| 1541 | the bitwise complement of the ``umask'' value. |
| 1542 | |
| 1543 | The argument @var{mode} must be an integer. On most systems, only the |
| 1544 | low 9 bits of @var{mode} are meaningful. You can use the Lisp construct |
| 1545 | for octal character codes to enter @var{mode}; for example, |
| 1546 | |
| 1547 | @example |
| 1548 | (set-default-file-modes ?\644) |
| 1549 | @end example |
| 1550 | |
| 1551 | Saving a modified version of an existing file does not count as creating |
| 1552 | the file; it preserves the existing file's mode, whatever that is. So |
| 1553 | the default file protection has no effect. |
| 1554 | @end defun |
| 1555 | |
| 1556 | @defun default-file-modes |
| 1557 | This function returns the current default protection value. |
| 1558 | @end defun |
| 1559 | |
| 1560 | @defun read-file-modes &optional prompt base-file |
| 1561 | This function reads file mode bits from the minibuffer. The optional |
| 1562 | argument @var{prompt} specifies a non-default prompt. Second optional |
| 1563 | argument @var{base-file} is the name of a file on whose permissions to |
| 1564 | base the mode bits that this function returns, if what the user types |
| 1565 | specifies mode bits relative to permissions of an existing file. |
| 1566 | |
| 1567 | If user input represents an octal number, this function returns that |
| 1568 | number. If it is a complete symbolic specification of mode bits, as |
| 1569 | in @code{"u=rwx"}, the function converts it to the equivalent numeric |
| 1570 | value using @code{file-modes-symbolic-to-number} and returns the |
| 1571 | result. If the specification is relative, as in @code{"o+g"}, then |
| 1572 | the permissions on which the specification is based are taken from the |
| 1573 | mode bits of @var{base-file}. If @var{base-file} is omitted or |
| 1574 | @code{nil}, the function uses @code{0} as the base mode bits. The |
| 1575 | complete and relative specifications can be combined, as in |
| 1576 | @code{"u+r,g+rx,o+r,g-w"}. @xref{File Permissions,,, coreutils, The |
| 1577 | @sc{gnu} @code{Coreutils} Manual}, for detailed description of |
| 1578 | symbolic mode bits specifications. |
| 1579 | @end defun |
| 1580 | |
| 1581 | @defun file-modes-symbolic-to-number modes &optional base-modes |
| 1582 | This subroutine converts a symbolic specification of file mode bits in |
| 1583 | @var{modes} into the equivalent numeric value. If the symbolic |
| 1584 | specification is based on an existing file, that file's mode bits are |
| 1585 | taken from the optional argument @var{base-modes}; if that argument is |
| 1586 | omitted or @code{nil}, it defaults to zero, i.e.@: no access rights at |
| 1587 | all. |
| 1588 | @end defun |
| 1589 | |
| 1590 | @defun set-file-times filename &optional time |
| 1591 | This function sets the access and modification times of @var{filename} |
| 1592 | to @var{time}. The return value is @code{t} if the times are successfully |
| 1593 | set, otherwise it is @code{nil}. @var{time} defaults to the current |
| 1594 | time and must be in the format returned by @code{current-time} |
| 1595 | (@pxref{Time of Day}). |
| 1596 | @end defun |
| 1597 | |
| 1598 | @node File Names |
| 1599 | @section File Names |
| 1600 | @cindex file names |
| 1601 | |
| 1602 | Files are generally referred to by their names, in Emacs as elsewhere. |
| 1603 | File names in Emacs are represented as strings. The functions that |
| 1604 | operate on a file all expect a file name argument. |
| 1605 | |
| 1606 | In addition to operating on files themselves, Emacs Lisp programs |
| 1607 | often need to operate on file names; i.e., to take them apart and to use |
| 1608 | part of a name to construct related file names. This section describes |
| 1609 | how to manipulate file names. |
| 1610 | |
| 1611 | The functions in this section do not actually access files, so they |
| 1612 | can operate on file names that do not refer to an existing file or |
| 1613 | directory. |
| 1614 | |
| 1615 | On MS-DOS and MS-Windows, these functions (like the function that |
| 1616 | actually operate on files) accept MS-DOS or MS-Windows file-name syntax, |
| 1617 | where backslashes separate the components, as well as Unix syntax; but |
| 1618 | they always return Unix syntax. This enables Lisp programs to specify |
| 1619 | file names in Unix syntax and work properly on all systems without |
| 1620 | change. |
| 1621 | |
| 1622 | @menu |
| 1623 | * File Name Components:: The directory part of a file name, and the rest. |
| 1624 | * Relative File Names:: Some file names are relative to a current directory. |
| 1625 | * Directory Names:: A directory's name as a directory |
| 1626 | is different from its name as a file. |
| 1627 | * File Name Expansion:: Converting relative file names to absolute ones. |
| 1628 | * Unique File Names:: Generating names for temporary files. |
| 1629 | * File Name Completion:: Finding the completions for a given file name. |
| 1630 | * Standard File Names:: If your package uses a fixed file name, |
| 1631 | how to handle various operating systems simply. |
| 1632 | @end menu |
| 1633 | |
| 1634 | @node File Name Components |
| 1635 | @subsection File Name Components |
| 1636 | @cindex directory part (of file name) |
| 1637 | @cindex nondirectory part (of file name) |
| 1638 | @cindex version number (in file name) |
| 1639 | |
| 1640 | The operating system groups files into directories. To specify a |
| 1641 | file, you must specify the directory and the file's name within that |
| 1642 | directory. Therefore, Emacs considers a file name as having two main |
| 1643 | parts: the @dfn{directory name} part, and the @dfn{nondirectory} part |
| 1644 | (or @dfn{file name within the directory}). Either part may be empty. |
| 1645 | Concatenating these two parts reproduces the original file name. |
| 1646 | |
| 1647 | On most systems, the directory part is everything up to and including |
| 1648 | the last slash (backslash is also allowed in input on MS-DOS or |
| 1649 | MS-Windows); the nondirectory part is the rest. |
| 1650 | |
| 1651 | For some purposes, the nondirectory part is further subdivided into |
| 1652 | the name proper and the @dfn{version number}. On most systems, only |
| 1653 | backup files have version numbers in their names. |
| 1654 | |
| 1655 | @defun file-name-directory filename |
| 1656 | This function returns the directory part of @var{filename}, as a |
| 1657 | directory name (@pxref{Directory Names}), or @code{nil} if |
| 1658 | @var{filename} does not include a directory part. |
| 1659 | |
| 1660 | On GNU and Unix systems, a string returned by this function always |
| 1661 | ends in a slash. On MS-DOS it can also end in a colon. |
| 1662 | |
| 1663 | @example |
| 1664 | @group |
| 1665 | (file-name-directory "lewis/foo") ; @r{Unix example} |
| 1666 | @result{} "lewis/" |
| 1667 | @end group |
| 1668 | @group |
| 1669 | (file-name-directory "foo") ; @r{Unix example} |
| 1670 | @result{} nil |
| 1671 | @end group |
| 1672 | @end example |
| 1673 | @end defun |
| 1674 | |
| 1675 | @defun file-name-nondirectory filename |
| 1676 | This function returns the nondirectory part of @var{filename}. |
| 1677 | |
| 1678 | @example |
| 1679 | @group |
| 1680 | (file-name-nondirectory "lewis/foo") |
| 1681 | @result{} "foo" |
| 1682 | @end group |
| 1683 | @group |
| 1684 | (file-name-nondirectory "foo") |
| 1685 | @result{} "foo" |
| 1686 | @end group |
| 1687 | @group |
| 1688 | (file-name-nondirectory "lewis/") |
| 1689 | @result{} "" |
| 1690 | @end group |
| 1691 | @end example |
| 1692 | @end defun |
| 1693 | |
| 1694 | @defun file-name-sans-versions filename &optional keep-backup-version |
| 1695 | This function returns @var{filename} with any file version numbers, |
| 1696 | backup version numbers, or trailing tildes discarded. |
| 1697 | |
| 1698 | If @var{keep-backup-version} is non-@code{nil}, then true file version |
| 1699 | numbers understood as such by the file system are discarded from the |
| 1700 | return value, but backup version numbers are kept. |
| 1701 | |
| 1702 | @example |
| 1703 | @group |
| 1704 | (file-name-sans-versions "~rms/foo.~1~") |
| 1705 | @result{} "~rms/foo" |
| 1706 | @end group |
| 1707 | @group |
| 1708 | (file-name-sans-versions "~rms/foo~") |
| 1709 | @result{} "~rms/foo" |
| 1710 | @end group |
| 1711 | @group |
| 1712 | (file-name-sans-versions "~rms/foo") |
| 1713 | @result{} "~rms/foo" |
| 1714 | @end group |
| 1715 | @end example |
| 1716 | @end defun |
| 1717 | |
| 1718 | @defun file-name-extension filename &optional period |
| 1719 | This function returns @var{filename}'s final ``extension,'' if any, |
| 1720 | after applying @code{file-name-sans-versions} to remove any |
| 1721 | version/backup part. The extension, in a file name, is the part that |
| 1722 | follows the last @samp{.} in the last name component (minus any |
| 1723 | version/backup part). |
| 1724 | |
| 1725 | This function returns @code{nil} for extensionless file names such as |
| 1726 | @file{foo}. It returns @code{""} for null extensions, as in |
| 1727 | @file{foo.}. If the last component of a file name begins with a |
| 1728 | @samp{.}, that @samp{.} doesn't count as the beginning of an |
| 1729 | extension. Thus, @file{.emacs}'s ``extension'' is @code{nil}, not |
| 1730 | @samp{.emacs}. |
| 1731 | |
| 1732 | If @var{period} is non-@code{nil}, then the returned value includes |
| 1733 | the period that delimits the extension, and if @var{filename} has no |
| 1734 | extension, the value is @code{""}. |
| 1735 | @end defun |
| 1736 | |
| 1737 | @defun file-name-sans-extension filename |
| 1738 | This function returns @var{filename} minus its extension, if any. The |
| 1739 | version/backup part, if present, is only removed if the file has an |
| 1740 | extension. For example, |
| 1741 | |
| 1742 | @example |
| 1743 | (file-name-sans-extension "foo.lose.c") |
| 1744 | @result{} "foo.lose" |
| 1745 | (file-name-sans-extension "big.hack/foo") |
| 1746 | @result{} "big.hack/foo" |
| 1747 | (file-name-sans-extension "/my/home/.emacs") |
| 1748 | @result{} "/my/home/.emacs" |
| 1749 | (file-name-sans-extension "/my/home/.emacs.el") |
| 1750 | @result{} "/my/home/.emacs" |
| 1751 | (file-name-sans-extension "~/foo.el.~3~") |
| 1752 | @result{} "~/foo" |
| 1753 | (file-name-sans-extension "~/foo.~3~") |
| 1754 | @result{} "~/foo.~3~" |
| 1755 | @end example |
| 1756 | |
| 1757 | Note that the @samp{.~3~} in the two last examples is the backup part, |
| 1758 | not an extension. |
| 1759 | @end defun |
| 1760 | |
| 1761 | @ignore |
| 1762 | Andrew Innes says that this |
| 1763 | |
| 1764 | @c @defvar directory-sep-char |
| 1765 | This variable holds the character that Emacs normally uses to separate |
| 1766 | file name components. The default value is @code{?/}, but on MS-Windows |
| 1767 | you can set it to @code{?\\}; then the functions that transform file names |
| 1768 | use backslashes in their output. |
| 1769 | |
| 1770 | File names using backslashes work as input to Lisp primitives even on |
| 1771 | MS-DOS and MS-Windows, even if @code{directory-sep-char} has its default |
| 1772 | value of @code{?/}. |
| 1773 | @end defvar |
| 1774 | @end ignore |
| 1775 | |
| 1776 | @node Relative File Names |
| 1777 | @subsection Absolute and Relative File Names |
| 1778 | @cindex absolute file name |
| 1779 | @cindex relative file name |
| 1780 | |
| 1781 | All the directories in the file system form a tree starting at the |
| 1782 | root directory. A file name can specify all the directory names |
| 1783 | starting from the root of the tree; then it is called an @dfn{absolute} |
| 1784 | file name. Or it can specify the position of the file in the tree |
| 1785 | relative to a default directory; then it is called a @dfn{relative} file |
| 1786 | name. On Unix and GNU/Linux, an absolute file name starts with a slash |
| 1787 | or a tilde (@samp{~}), and a relative one does not. On MS-DOS and |
| 1788 | MS-Windows, an absolute file name starts with a slash or a backslash, or |
| 1789 | with a drive specification @samp{@var{x}:/}, where @var{x} is the |
| 1790 | @dfn{drive letter}. |
| 1791 | |
| 1792 | @defun file-name-absolute-p filename |
| 1793 | This function returns @code{t} if file @var{filename} is an absolute |
| 1794 | file name, @code{nil} otherwise. |
| 1795 | |
| 1796 | @example |
| 1797 | @group |
| 1798 | (file-name-absolute-p "~rms/foo") |
| 1799 | @result{} t |
| 1800 | @end group |
| 1801 | @group |
| 1802 | (file-name-absolute-p "rms/foo") |
| 1803 | @result{} nil |
| 1804 | @end group |
| 1805 | @group |
| 1806 | (file-name-absolute-p "/user/rms/foo") |
| 1807 | @result{} t |
| 1808 | @end group |
| 1809 | @end example |
| 1810 | @end defun |
| 1811 | |
| 1812 | Given a possibly relative file name, you can convert it to an |
| 1813 | absolute name using @code{expand-file-name} (@pxref{File Name |
| 1814 | Expansion}). This function converts absolute file names to relative |
| 1815 | names: |
| 1816 | |
| 1817 | @defun file-relative-name filename &optional directory |
| 1818 | This function tries to return a relative name that is equivalent to |
| 1819 | @var{filename}, assuming the result will be interpreted relative to |
| 1820 | @var{directory} (an absolute directory name or directory file name). |
| 1821 | If @var{directory} is omitted or @code{nil}, it defaults to the |
| 1822 | current buffer's default directory. |
| 1823 | |
| 1824 | On some operating systems, an absolute file name begins with a device |
| 1825 | name. On such systems, @var{filename} has no relative equivalent based |
| 1826 | on @var{directory} if they start with two different device names. In |
| 1827 | this case, @code{file-relative-name} returns @var{filename} in absolute |
| 1828 | form. |
| 1829 | |
| 1830 | @example |
| 1831 | (file-relative-name "/foo/bar" "/foo/") |
| 1832 | @result{} "bar" |
| 1833 | (file-relative-name "/foo/bar" "/hack/") |
| 1834 | @result{} "../foo/bar" |
| 1835 | @end example |
| 1836 | @end defun |
| 1837 | |
| 1838 | @node Directory Names |
| 1839 | @comment node-name, next, previous, up |
| 1840 | @subsection Directory Names |
| 1841 | @cindex directory name |
| 1842 | @cindex file name of directory |
| 1843 | |
| 1844 | A @dfn{directory name} is the name of a directory. A directory is |
| 1845 | actually a kind of file, so it has a file name, which is related to |
| 1846 | the directory name but not identical to it. (This is not quite the |
| 1847 | same as the usual Unix terminology.) These two different names for |
| 1848 | the same entity are related by a syntactic transformation. On GNU and |
| 1849 | Unix systems, this is simple: a directory name ends in a slash, |
| 1850 | whereas the directory's name as a file lacks that slash. On MS-DOS |
| 1851 | the relationship is more complicated. |
| 1852 | |
| 1853 | The difference between a directory name and its name as a file is |
| 1854 | subtle but crucial. When an Emacs variable or function argument is |
| 1855 | described as being a directory name, a file name of a directory is not |
| 1856 | acceptable. When @code{file-name-directory} returns a string, that is |
| 1857 | always a directory name. |
| 1858 | |
| 1859 | The following two functions convert between directory names and file |
| 1860 | names. They do nothing special with environment variable substitutions |
| 1861 | such as @samp{$HOME}, and the constructs @samp{~}, @samp{.} and @samp{..}. |
| 1862 | |
| 1863 | @defun file-name-as-directory filename |
| 1864 | This function returns a string representing @var{filename} in a form |
| 1865 | that the operating system will interpret as the name of a directory. On |
| 1866 | most systems, this means appending a slash to the string (if it does not |
| 1867 | already end in one). |
| 1868 | |
| 1869 | @example |
| 1870 | @group |
| 1871 | (file-name-as-directory "~rms/lewis") |
| 1872 | @result{} "~rms/lewis/" |
| 1873 | @end group |
| 1874 | @end example |
| 1875 | @end defun |
| 1876 | |
| 1877 | @defun directory-file-name dirname |
| 1878 | This function returns a string representing @var{dirname} in a form that |
| 1879 | the operating system will interpret as the name of a file. On most |
| 1880 | systems, this means removing the final slash (or backslash) from the |
| 1881 | string. |
| 1882 | |
| 1883 | @example |
| 1884 | @group |
| 1885 | (directory-file-name "~lewis/") |
| 1886 | @result{} "~lewis" |
| 1887 | @end group |
| 1888 | @end example |
| 1889 | @end defun |
| 1890 | |
| 1891 | Given a directory name, you can combine it with a relative file name |
| 1892 | using @code{concat}: |
| 1893 | |
| 1894 | @example |
| 1895 | (concat @var{dirname} @var{relfile}) |
| 1896 | @end example |
| 1897 | |
| 1898 | @noindent |
| 1899 | Be sure to verify that the file name is relative before doing that. |
| 1900 | If you use an absolute file name, the results could be syntactically |
| 1901 | invalid or refer to the wrong file. |
| 1902 | |
| 1903 | If you want to use a directory file name in making such a |
| 1904 | combination, you must first convert it to a directory name using |
| 1905 | @code{file-name-as-directory}: |
| 1906 | |
| 1907 | @example |
| 1908 | (concat (file-name-as-directory @var{dirfile}) @var{relfile}) |
| 1909 | @end example |
| 1910 | |
| 1911 | @noindent |
| 1912 | Don't try concatenating a slash by hand, as in |
| 1913 | |
| 1914 | @example |
| 1915 | ;;; @r{Wrong!} |
| 1916 | (concat @var{dirfile} "/" @var{relfile}) |
| 1917 | @end example |
| 1918 | |
| 1919 | @noindent |
| 1920 | because this is not portable. Always use |
| 1921 | @code{file-name-as-directory}. |
| 1922 | |
| 1923 | @cindex directory name abbreviation |
| 1924 | Directory name abbreviations are useful for directories that are |
| 1925 | normally accessed through symbolic links. Sometimes the users recognize |
| 1926 | primarily the link's name as ``the name'' of the directory, and find it |
| 1927 | annoying to see the directory's ``real'' name. If you define the link |
| 1928 | name as an abbreviation for the ``real'' name, Emacs shows users the |
| 1929 | abbreviation instead. |
| 1930 | |
| 1931 | @defopt directory-abbrev-alist |
| 1932 | The variable @code{directory-abbrev-alist} contains an alist of |
| 1933 | abbreviations to use for file directories. Each element has the form |
| 1934 | @code{(@var{from} . @var{to})}, and says to replace @var{from} with |
| 1935 | @var{to} when it appears in a directory name. The @var{from} string is |
| 1936 | actually a regular expression; it should always start with @samp{^}. |
| 1937 | The @var{to} string should be an ordinary absolute directory name. Do |
| 1938 | not use @samp{~} to stand for a home directory in that string. The |
| 1939 | function @code{abbreviate-file-name} performs these substitutions. |
| 1940 | |
| 1941 | You can set this variable in @file{site-init.el} to describe the |
| 1942 | abbreviations appropriate for your site. |
| 1943 | |
| 1944 | Here's an example, from a system on which file system @file{/home/fsf} |
| 1945 | and so on are normally accessed through symbolic links named @file{/fsf} |
| 1946 | and so on. |
| 1947 | |
| 1948 | @example |
| 1949 | (("^/home/fsf" . "/fsf") |
| 1950 | ("^/home/gp" . "/gp") |
| 1951 | ("^/home/gd" . "/gd")) |
| 1952 | @end example |
| 1953 | @end defopt |
| 1954 | |
| 1955 | To convert a directory name to its abbreviation, use this |
| 1956 | function: |
| 1957 | |
| 1958 | @defun abbreviate-file-name filename |
| 1959 | @anchor{Definition of abbreviate-file-name} |
| 1960 | This function applies abbreviations from @code{directory-abbrev-alist} |
| 1961 | to its argument, and also substitutes @samp{~} for the user's home |
| 1962 | directory if the argument names a file in the home directory or one of |
| 1963 | its subdirectories. (If the home directory is a root directory, it is |
| 1964 | not replaced with @samp{~}, because this does not make the result |
| 1965 | shorter on many systems.) You can use it for directory names and for |
| 1966 | file names, because it recognizes abbreviations even as part of the |
| 1967 | name. |
| 1968 | @end defun |
| 1969 | |
| 1970 | @node File Name Expansion |
| 1971 | @subsection Functions that Expand Filenames |
| 1972 | @cindex expansion of file names |
| 1973 | |
| 1974 | @dfn{Expansion} of a file name means converting a relative file name |
| 1975 | to an absolute one. Since this is done relative to a default directory, |
| 1976 | you must specify the default directory name as well as the file name to |
| 1977 | be expanded. Expansion also simplifies file names by eliminating |
| 1978 | redundancies such as @file{./} and @file{@var{name}/../}. |
| 1979 | |
| 1980 | @defun expand-file-name filename &optional directory |
| 1981 | This function converts @var{filename} to an absolute file name. If |
| 1982 | @var{directory} is supplied, it is the default directory to start with |
| 1983 | if @var{filename} is relative. (The value of @var{directory} should |
| 1984 | itself be an absolute directory name or directory file name; it may |
| 1985 | start with @samp{~}.) Otherwise, the current buffer's value of |
| 1986 | @code{default-directory} is used. For example: |
| 1987 | |
| 1988 | @example |
| 1989 | @group |
| 1990 | (expand-file-name "foo") |
| 1991 | @result{} "/xcssun/users/rms/lewis/foo" |
| 1992 | @end group |
| 1993 | @group |
| 1994 | (expand-file-name "../foo") |
| 1995 | @result{} "/xcssun/users/rms/foo" |
| 1996 | @end group |
| 1997 | @group |
| 1998 | (expand-file-name "foo" "/usr/spool/") |
| 1999 | @result{} "/usr/spool/foo" |
| 2000 | @end group |
| 2001 | @group |
| 2002 | (expand-file-name "$HOME/foo") |
| 2003 | @result{} "/xcssun/users/rms/lewis/$HOME/foo" |
| 2004 | @end group |
| 2005 | @end example |
| 2006 | |
| 2007 | If the part of the combined file name before the first slash is |
| 2008 | @samp{~}, it expands to the value of the @env{HOME} environment |
| 2009 | variable (usually your home directory). If the part before the first |
| 2010 | slash is @samp{~@var{user}} and if @var{user} is a valid login name, |
| 2011 | it expands to @var{user}'s home directory. |
| 2012 | |
| 2013 | Filenames containing @samp{.} or @samp{..} are simplified to their |
| 2014 | canonical form: |
| 2015 | |
| 2016 | @example |
| 2017 | @group |
| 2018 | (expand-file-name "bar/../foo") |
| 2019 | @result{} "/xcssun/users/rms/lewis/foo" |
| 2020 | @end group |
| 2021 | @end example |
| 2022 | |
| 2023 | In some cases, a leading @samp{..} component can remain in the output: |
| 2024 | |
| 2025 | @example |
| 2026 | @group |
| 2027 | (expand-file-name "../home" "/") |
| 2028 | @result{} "/../home" |
| 2029 | @end group |
| 2030 | @end example |
| 2031 | |
| 2032 | @noindent |
| 2033 | This is for the sake of filesystems that have the concept of a |
| 2034 | ``superroot'' above the root directory @file{/}. On other filesystems, |
| 2035 | @file{/../} is interpreted exactly the same as @file{/}. |
| 2036 | |
| 2037 | Note that @code{expand-file-name} does @emph{not} expand environment |
| 2038 | variables; only @code{substitute-in-file-name} does that. |
| 2039 | |
| 2040 | Note also that @code{expand-file-name} does not follow symbolic links |
| 2041 | at any level. This results in a difference between the way |
| 2042 | @code{file-truename} and @code{expand-file-name} treat @samp{..}. |
| 2043 | Assuming that @samp{/tmp/bar} is a symbolic link to the directory |
| 2044 | @samp{/tmp/foo/bar} we get: |
| 2045 | |
| 2046 | @example |
| 2047 | @group |
| 2048 | (file-truename "/tmp/bar/../myfile") |
| 2049 | @result{} "/tmp/foo/myfile" |
| 2050 | @end group |
| 2051 | @group |
| 2052 | (expand-file-name "/tmp/bar/../myfile") |
| 2053 | @result{} "/tmp/myfile" |
| 2054 | @end group |
| 2055 | @end example |
| 2056 | |
| 2057 | If you may need to follow symbolic links preceding @samp{..}, you |
| 2058 | should make sure to call @code{file-truename} without prior direct or |
| 2059 | indirect calls to @code{expand-file-name}. @xref{Truenames}. |
| 2060 | @end defun |
| 2061 | |
| 2062 | @defvar default-directory |
| 2063 | The value of this buffer-local variable is the default directory for the |
| 2064 | current buffer. It should be an absolute directory name; it may start |
| 2065 | with @samp{~}. This variable is buffer-local in every buffer. |
| 2066 | |
| 2067 | @code{expand-file-name} uses the default directory when its second |
| 2068 | argument is @code{nil}. |
| 2069 | |
| 2070 | The value is always a string ending with a slash. |
| 2071 | |
| 2072 | @example |
| 2073 | @group |
| 2074 | default-directory |
| 2075 | @result{} "/user/lewis/manual/" |
| 2076 | @end group |
| 2077 | @end example |
| 2078 | @end defvar |
| 2079 | |
| 2080 | @defun substitute-in-file-name filename |
| 2081 | @anchor{Definition of substitute-in-file-name} |
| 2082 | This function replaces environment variable references in |
| 2083 | @var{filename} with the environment variable values. Following |
| 2084 | standard Unix shell syntax, @samp{$} is the prefix to substitute an |
| 2085 | environment variable value. If the input contains @samp{$$}, that is |
| 2086 | converted to @samp{$}; this gives the user a way to ``quote'' a |
| 2087 | @samp{$}. |
| 2088 | |
| 2089 | The environment variable name is the series of alphanumeric characters |
| 2090 | (including underscores) that follow the @samp{$}. If the character following |
| 2091 | the @samp{$} is a @samp{@{}, then the variable name is everything up to the |
| 2092 | matching @samp{@}}. |
| 2093 | |
| 2094 | Calling @code{substitute-in-file-name} on output produced by |
| 2095 | @code{substitute-in-file-name} tends to give incorrect results. For |
| 2096 | instance, use of @samp{$$} to quote a single @samp{$} won't work |
| 2097 | properly, and @samp{$} in an environment variable's value could lead |
| 2098 | to repeated substitution. Therefore, programs that call this function |
| 2099 | and put the output where it will be passed to this function need to |
| 2100 | double all @samp{$} characters to prevent subsequent incorrect |
| 2101 | results. |
| 2102 | |
| 2103 | @c Wordy to avoid overfull hbox. --rjc 15mar92 |
| 2104 | Here we assume that the environment variable @code{HOME}, which holds |
| 2105 | the user's home directory name, has value @samp{/xcssun/users/rms}. |
| 2106 | |
| 2107 | @example |
| 2108 | @group |
| 2109 | (substitute-in-file-name "$HOME/foo") |
| 2110 | @result{} "/xcssun/users/rms/foo" |
| 2111 | @end group |
| 2112 | @end example |
| 2113 | |
| 2114 | After substitution, if a @samp{~} or a @samp{/} appears immediately |
| 2115 | after another @samp{/}, the function discards everything before it (up |
| 2116 | through the immediately preceding @samp{/}). |
| 2117 | |
| 2118 | @example |
| 2119 | @group |
| 2120 | (substitute-in-file-name "bar/~/foo") |
| 2121 | @result{} "~/foo" |
| 2122 | @end group |
| 2123 | @group |
| 2124 | (substitute-in-file-name "/usr/local/$HOME/foo") |
| 2125 | @result{} "/xcssun/users/rms/foo" |
| 2126 | ;; @r{@file{/usr/local/} has been discarded.} |
| 2127 | @end group |
| 2128 | @end example |
| 2129 | |
| 2130 | @end defun |
| 2131 | |
| 2132 | @node Unique File Names |
| 2133 | @subsection Generating Unique File Names |
| 2134 | |
| 2135 | Some programs need to write temporary files. Here is the usual way to |
| 2136 | construct a name for such a file: |
| 2137 | |
| 2138 | @example |
| 2139 | (make-temp-file @var{name-of-application}) |
| 2140 | @end example |
| 2141 | |
| 2142 | @noindent |
| 2143 | The job of @code{make-temp-file} is to prevent two different users or |
| 2144 | two different jobs from trying to use the exact same file name. |
| 2145 | |
| 2146 | @defun make-temp-file prefix &optional dir-flag suffix |
| 2147 | This function creates a temporary file and returns its name. Emacs |
| 2148 | creates the temporary file's name by adding to @var{prefix} some |
| 2149 | random characters that are different in each Emacs job. The result is |
| 2150 | guaranteed to be a newly created empty file. On MS-DOS, this function |
| 2151 | can truncate the @var{string} prefix to fit into the 8+3 file-name |
| 2152 | limits. If @var{prefix} is a relative file name, it is expanded |
| 2153 | against @code{temporary-file-directory}. |
| 2154 | |
| 2155 | @example |
| 2156 | @group |
| 2157 | (make-temp-file "foo") |
| 2158 | @result{} "/tmp/foo232J6v" |
| 2159 | @end group |
| 2160 | @end example |
| 2161 | |
| 2162 | When @code{make-temp-file} returns, the file has been created and is |
| 2163 | empty. At that point, you should write the intended contents into the |
| 2164 | file. |
| 2165 | |
| 2166 | If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an |
| 2167 | empty directory instead of an empty file. It returns the file name, |
| 2168 | not the directory name, of that directory. @xref{Directory Names}. |
| 2169 | |
| 2170 | If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at |
| 2171 | the end of the file name. |
| 2172 | |
| 2173 | To prevent conflicts among different libraries running in the same |
| 2174 | Emacs, each Lisp program that uses @code{make-temp-file} should have its |
| 2175 | own @var{prefix}. The number added to the end of @var{prefix} |
| 2176 | distinguishes between the same application running in different Emacs |
| 2177 | jobs. Additional added characters permit a large number of distinct |
| 2178 | names even in one Emacs job. |
| 2179 | @end defun |
| 2180 | |
| 2181 | The default directory for temporary files is controlled by the |
| 2182 | variable @code{temporary-file-directory}. This variable gives the user |
| 2183 | a uniform way to specify the directory for all temporary files. Some |
| 2184 | programs use @code{small-temporary-file-directory} instead, if that is |
| 2185 | non-@code{nil}. To use it, you should expand the prefix against |
| 2186 | the proper directory before calling @code{make-temp-file}. |
| 2187 | |
| 2188 | In older Emacs versions where @code{make-temp-file} does not exist, |
| 2189 | you should use @code{make-temp-name} instead: |
| 2190 | |
| 2191 | @example |
| 2192 | (make-temp-name |
| 2193 | (expand-file-name @var{name-of-application} |
| 2194 | temporary-file-directory)) |
| 2195 | @end example |
| 2196 | |
| 2197 | @defun make-temp-name string |
| 2198 | This function generates a string that can be used as a unique file |
| 2199 | name. The name starts with @var{string}, and has several random |
| 2200 | characters appended to it, which are different in each Emacs job. It |
| 2201 | is like @code{make-temp-file} except that it just constructs a name, |
| 2202 | and does not create a file. Another difference is that @var{string} |
| 2203 | should be an absolute file name. On MS-DOS, this function can |
| 2204 | truncate the @var{string} prefix to fit into the 8+3 file-name limits. |
| 2205 | @end defun |
| 2206 | |
| 2207 | @defopt temporary-file-directory |
| 2208 | @cindex @code{TMPDIR} environment variable |
| 2209 | @cindex @code{TMP} environment variable |
| 2210 | @cindex @code{TEMP} environment variable |
| 2211 | This variable specifies the directory name for creating temporary files. |
| 2212 | Its value should be a directory name (@pxref{Directory Names}), but it |
| 2213 | is good for Lisp programs to cope if the value is a directory's file |
| 2214 | name instead. Using the value as the second argument to |
| 2215 | @code{expand-file-name} is a good way to achieve that. |
| 2216 | |
| 2217 | The default value is determined in a reasonable way for your operating |
| 2218 | system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP} |
| 2219 | environment variables, with a fall-back to a system-dependent name if |
| 2220 | none of these variables is defined. |
| 2221 | |
| 2222 | Even if you do not use @code{make-temp-file} to create the temporary |
| 2223 | file, you should still use this variable to decide which directory to |
| 2224 | put the file in. However, if you expect the file to be small, you |
| 2225 | should use @code{small-temporary-file-directory} first if that is |
| 2226 | non-@code{nil}. |
| 2227 | @end defopt |
| 2228 | |
| 2229 | @defopt small-temporary-file-directory |
| 2230 | This variable specifies the directory name for |
| 2231 | creating certain temporary files, which are likely to be small. |
| 2232 | |
| 2233 | If you want to write a temporary file which is likely to be small, you |
| 2234 | should compute the directory like this: |
| 2235 | |
| 2236 | @example |
| 2237 | (make-temp-file |
| 2238 | (expand-file-name @var{prefix} |
| 2239 | (or small-temporary-file-directory |
| 2240 | temporary-file-directory))) |
| 2241 | @end example |
| 2242 | @end defopt |
| 2243 | |
| 2244 | @node File Name Completion |
| 2245 | @subsection File Name Completion |
| 2246 | @cindex file name completion subroutines |
| 2247 | @cindex completion, file name |
| 2248 | |
| 2249 | This section describes low-level subroutines for completing a file |
| 2250 | name. For higher level functions, see @ref{Reading File Names}. |
| 2251 | |
| 2252 | @defun file-name-all-completions partial-filename directory |
| 2253 | This function returns a list of all possible completions for a file |
| 2254 | whose name starts with @var{partial-filename} in directory |
| 2255 | @var{directory}. The order of the completions is the order of the files |
| 2256 | in the directory, which is unpredictable and conveys no useful |
| 2257 | information. |
| 2258 | |
| 2259 | The argument @var{partial-filename} must be a file name containing no |
| 2260 | directory part and no slash (or backslash on some systems). The current |
| 2261 | buffer's default directory is prepended to @var{directory}, if |
| 2262 | @var{directory} is not absolute. |
| 2263 | |
| 2264 | In the following example, suppose that @file{~rms/lewis} is the current |
| 2265 | default directory, and has five files whose names begin with @samp{f}: |
| 2266 | @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and |
| 2267 | @file{file.c.~2~}.@refill |
| 2268 | |
| 2269 | @example |
| 2270 | @group |
| 2271 | (file-name-all-completions "f" "") |
| 2272 | @result{} ("foo" "file~" "file.c.~2~" |
| 2273 | "file.c.~1~" "file.c") |
| 2274 | @end group |
| 2275 | |
| 2276 | @group |
| 2277 | (file-name-all-completions "fo" "") |
| 2278 | @result{} ("foo") |
| 2279 | @end group |
| 2280 | @end example |
| 2281 | @end defun |
| 2282 | |
| 2283 | @defun file-name-completion filename directory &optional predicate |
| 2284 | This function completes the file name @var{filename} in directory |
| 2285 | @var{directory}. It returns the longest prefix common to all file names |
| 2286 | in directory @var{directory} that start with @var{filename}. If |
| 2287 | @var{predicate} is non-@code{nil} then it ignores possible completions |
| 2288 | that don't satisfy @var{predicate}, after calling that function |
| 2289 | with one argument, the expanded absolute file name. |
| 2290 | |
| 2291 | If only one match exists and @var{filename} matches it exactly, the |
| 2292 | function returns @code{t}. The function returns @code{nil} if directory |
| 2293 | @var{directory} contains no name starting with @var{filename}. |
| 2294 | |
| 2295 | In the following example, suppose that the current default directory |
| 2296 | has five files whose names begin with @samp{f}: @file{foo}, |
| 2297 | @file{file~}, @file{file.c}, @file{file.c.~1~}, and |
| 2298 | @file{file.c.~2~}.@refill |
| 2299 | |
| 2300 | @example |
| 2301 | @group |
| 2302 | (file-name-completion "fi" "") |
| 2303 | @result{} "file" |
| 2304 | @end group |
| 2305 | |
| 2306 | @group |
| 2307 | (file-name-completion "file.c.~1" "") |
| 2308 | @result{} "file.c.~1~" |
| 2309 | @end group |
| 2310 | |
| 2311 | @group |
| 2312 | (file-name-completion "file.c.~1~" "") |
| 2313 | @result{} t |
| 2314 | @end group |
| 2315 | |
| 2316 | @group |
| 2317 | (file-name-completion "file.c.~3" "") |
| 2318 | @result{} nil |
| 2319 | @end group |
| 2320 | @end example |
| 2321 | @end defun |
| 2322 | |
| 2323 | @defopt completion-ignored-extensions |
| 2324 | @code{file-name-completion} usually ignores file names that end in any |
| 2325 | string in this list. It does not ignore them when all the possible |
| 2326 | completions end in one of these suffixes. This variable has no effect |
| 2327 | on @code{file-name-all-completions}.@refill |
| 2328 | |
| 2329 | A typical value might look like this: |
| 2330 | |
| 2331 | @example |
| 2332 | @group |
| 2333 | completion-ignored-extensions |
| 2334 | @result{} (".o" ".elc" "~" ".dvi") |
| 2335 | @end group |
| 2336 | @end example |
| 2337 | |
| 2338 | If an element of @code{completion-ignored-extensions} ends in a slash |
| 2339 | @samp{/}, it signals a directory. The elements which do @emph{not} end |
| 2340 | in a slash will never match a directory; thus, the above value will not |
| 2341 | filter out a directory named @file{foo.elc}. |
| 2342 | @end defopt |
| 2343 | |
| 2344 | @node Standard File Names |
| 2345 | @subsection Standard File Names |
| 2346 | |
| 2347 | Most of the file names used in Lisp programs are entered by the user. |
| 2348 | But occasionally a Lisp program needs to specify a standard file name |
| 2349 | for a particular use---typically, to hold customization information |
| 2350 | about each user. For example, abbrev definitions are stored (by |
| 2351 | default) in the file @file{~/.abbrev_defs}; the @code{completion} |
| 2352 | package stores completions in the file @file{~/.completions}. These are |
| 2353 | two of the many standard file names used by parts of Emacs for certain |
| 2354 | purposes. |
| 2355 | |
| 2356 | Various operating systems have their own conventions for valid file |
| 2357 | names and for which file names to use for user profile data. A Lisp |
| 2358 | program which reads a file using a standard file name ought to use, on |
| 2359 | each type of system, a file name suitable for that system. The function |
| 2360 | @code{convert-standard-filename} makes this easy to do. |
| 2361 | |
| 2362 | @defun convert-standard-filename filename |
| 2363 | This function alters the file name @var{filename} to fit the conventions |
| 2364 | of the operating system in use, and returns the result as a new string. |
| 2365 | @end defun |
| 2366 | |
| 2367 | The recommended way to specify a standard file name in a Lisp program |
| 2368 | is to choose a name which fits the conventions of GNU and Unix systems, |
| 2369 | usually with a nondirectory part that starts with a period, and pass it |
| 2370 | to @code{convert-standard-filename} instead of using it directly. Here |
| 2371 | is an example from the @code{completion} package: |
| 2372 | |
| 2373 | @example |
| 2374 | (defvar save-completions-file-name |
| 2375 | (convert-standard-filename "~/.completions") |
| 2376 | "*The file name to save completions to.") |
| 2377 | @end example |
| 2378 | |
| 2379 | On GNU and Unix systems, and on some other systems as well, |
| 2380 | @code{convert-standard-filename} returns its argument unchanged. On |
| 2381 | some other systems, it alters the name to fit the system's conventions. |
| 2382 | |
| 2383 | For example, on MS-DOS the alterations made by this function include |
| 2384 | converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the |
| 2385 | middle of the name to @samp{.} if there is no other @samp{.}, inserting |
| 2386 | a @samp{.} after eight characters if there is none, and truncating to |
| 2387 | three characters after the @samp{.}. (It makes other changes as well.) |
| 2388 | Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and |
| 2389 | @file{.completions} becomes @file{_complet.ion}. |
| 2390 | |
| 2391 | @node Contents of Directories |
| 2392 | @section Contents of Directories |
| 2393 | @cindex directory-oriented functions |
| 2394 | @cindex file names in directory |
| 2395 | |
| 2396 | A directory is a kind of file that contains other files entered under |
| 2397 | various names. Directories are a feature of the file system. |
| 2398 | |
| 2399 | Emacs can list the names of the files in a directory as a Lisp list, |
| 2400 | or display the names in a buffer using the @code{ls} shell command. In |
| 2401 | the latter case, it can optionally display information about each file, |
| 2402 | depending on the options passed to the @code{ls} command. |
| 2403 | |
| 2404 | @defun directory-files directory &optional full-name match-regexp nosort |
| 2405 | This function returns a list of the names of the files in the directory |
| 2406 | @var{directory}. By default, the list is in alphabetical order. |
| 2407 | |
| 2408 | If @var{full-name} is non-@code{nil}, the function returns the files' |
| 2409 | absolute file names. Otherwise, it returns the names relative to |
| 2410 | the specified directory. |
| 2411 | |
| 2412 | If @var{match-regexp} is non-@code{nil}, this function returns only |
| 2413 | those file names that contain a match for that regular expression---the |
| 2414 | other file names are excluded from the list. On case-insensitive |
| 2415 | filesystems, the regular expression matching is case-insensitive. |
| 2416 | |
| 2417 | @c Emacs 19 feature |
| 2418 | If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort |
| 2419 | the list, so you get the file names in no particular order. Use this if |
| 2420 | you want the utmost possible speed and don't care what order the files |
| 2421 | are processed in. If the order of processing is visible to the user, |
| 2422 | then the user will probably be happier if you do sort the names. |
| 2423 | |
| 2424 | @example |
| 2425 | @group |
| 2426 | (directory-files "~lewis") |
| 2427 | @result{} ("#foo#" "#foo.el#" "." ".." |
| 2428 | "dired-mods.el" "files.texi" |
| 2429 | "files.texi.~1~") |
| 2430 | @end group |
| 2431 | @end example |
| 2432 | |
| 2433 | An error is signaled if @var{directory} is not the name of a directory |
| 2434 | that can be read. |
| 2435 | @end defun |
| 2436 | |
| 2437 | @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format |
| 2438 | This is similar to @code{directory-files} in deciding which files |
| 2439 | to report on and how to report their names. However, instead |
| 2440 | of returning a list of file names, it returns for each file a |
| 2441 | list @code{(@var{filename} . @var{attributes})}, where @var{attributes} |
| 2442 | is what @code{file-attributes} would return for that file. |
| 2443 | The optional argument @var{id-format} has the same meaning as the |
| 2444 | corresponding argument to @code{file-attributes} (@pxref{Definition |
| 2445 | of file-attributes}). |
| 2446 | @end defun |
| 2447 | |
| 2448 | @defun file-expand-wildcards pattern &optional full |
| 2449 | This function expands the wildcard pattern @var{pattern}, returning |
| 2450 | a list of file names that match it. |
| 2451 | |
| 2452 | If @var{pattern} is written as an absolute file name, |
| 2453 | the values are absolute also. |
| 2454 | |
| 2455 | If @var{pattern} is written as a relative file name, it is interpreted |
| 2456 | relative to the current default directory. The file names returned are |
| 2457 | normally also relative to the current default directory. However, if |
| 2458 | @var{full} is non-@code{nil}, they are absolute. |
| 2459 | @end defun |
| 2460 | |
| 2461 | @defun insert-directory file switches &optional wildcard full-directory-p |
| 2462 | This function inserts (in the current buffer) a directory listing for |
| 2463 | directory @var{file}, formatted with @code{ls} according to |
| 2464 | @var{switches}. It leaves point after the inserted text. |
| 2465 | @var{switches} may be a string of options, or a list of strings |
| 2466 | representing individual options. |
| 2467 | |
| 2468 | The argument @var{file} may be either a directory name or a file |
| 2469 | specification including wildcard characters. If @var{wildcard} is |
| 2470 | non-@code{nil}, that means treat @var{file} as a file specification with |
| 2471 | wildcards. |
| 2472 | |
| 2473 | If @var{full-directory-p} is non-@code{nil}, that means the directory |
| 2474 | listing is expected to show the full contents of a directory. You |
| 2475 | should specify @code{t} when @var{file} is a directory and switches do |
| 2476 | not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to |
| 2477 | describe a directory itself as a file, rather than showing its |
| 2478 | contents.) |
| 2479 | |
| 2480 | On most systems, this function works by running a directory listing |
| 2481 | program whose name is in the variable @code{insert-directory-program}. |
| 2482 | If @var{wildcard} is non-@code{nil}, it also runs the shell specified by |
| 2483 | @code{shell-file-name}, to expand the wildcards. |
| 2484 | |
| 2485 | MS-DOS and MS-Windows systems usually lack the standard Unix program |
| 2486 | @code{ls}, so this function emulates the standard Unix program @code{ls} |
| 2487 | with Lisp code. |
| 2488 | |
| 2489 | As a technical detail, when @var{switches} contains the long |
| 2490 | @samp{--dired} option, @code{insert-directory} treats it specially, |
| 2491 | for the sake of dired. However, the normally equivalent short |
| 2492 | @samp{-D} option is just passed on to @code{insert-directory-program}, |
| 2493 | as any other option. |
| 2494 | @end defun |
| 2495 | |
| 2496 | @defvar insert-directory-program |
| 2497 | This variable's value is the program to run to generate a directory listing |
| 2498 | for the function @code{insert-directory}. It is ignored on systems |
| 2499 | which generate the listing with Lisp code. |
| 2500 | @end defvar |
| 2501 | |
| 2502 | @node Create/Delete Dirs |
| 2503 | @section Creating, Copying and Deleting Directories |
| 2504 | @cindex creating, copying and deleting directories |
| 2505 | @c Emacs 19 features |
| 2506 | |
| 2507 | Most Emacs Lisp file-manipulation functions get errors when used on |
| 2508 | files that are directories. For example, you cannot delete a directory |
| 2509 | with @code{delete-file}. These special functions exist to create and |
| 2510 | delete directories. |
| 2511 | |
| 2512 | @findex mkdir |
| 2513 | @deffn Command make-directory dirname &optional parents |
| 2514 | This command creates a directory named @var{dirname}. If |
| 2515 | @var{parents} is non-@code{nil}, as is always the case in an |
| 2516 | interactive call, that means to create the parent directories first, |
| 2517 | if they don't already exist. |
| 2518 | |
| 2519 | @code{mkdir} is an alias for this. |
| 2520 | @end deffn |
| 2521 | |
| 2522 | @deffn Command copy-directory dirname newname &optional keep-time parents |
| 2523 | This command copies the directory named @var{dirname} to |
| 2524 | @var{newname}. If @var{newname} names an existing directory, |
| 2525 | @var{dirname} will be copied to a subdirectory there. |
| 2526 | |
| 2527 | It always sets the file modes of the copied files to match the |
| 2528 | corresponding original file. |
| 2529 | |
| 2530 | The third arg @var{keep-time} non-@code{nil} means to preserve the |
| 2531 | modification time of the copied files. A prefix arg makes |
| 2532 | @var{keep-time} non-@code{nil}. |
| 2533 | |
| 2534 | Noninteractively, the last argument @var{parents} says whether to |
| 2535 | create parent directories if they don't exist. Interactively, |
| 2536 | this happens by default. |
| 2537 | @end deffn |
| 2538 | |
| 2539 | @deffn Command delete-directory dirname &optional recursive |
| 2540 | This command deletes the directory named @var{dirname}. The function |
| 2541 | @code{delete-file} does not work for files that are directories; you |
| 2542 | must use @code{delete-directory} for them. If @var{recursive} is |
| 2543 | @code{nil}, and the directory contains any files, |
| 2544 | @code{delete-directory} signals an error. |
| 2545 | |
| 2546 | @code{delete-directory} only follows symbolic links at the level of |
| 2547 | parent directories. |
| 2548 | @end deffn |
| 2549 | |
| 2550 | @node Magic File Names |
| 2551 | @section Making Certain File Names ``Magic'' |
| 2552 | @cindex magic file names |
| 2553 | |
| 2554 | @c Emacs 19 feature |
| 2555 | You can implement special handling for certain file names. This is |
| 2556 | called making those names @dfn{magic}. The principal use for this |
| 2557 | feature is in implementing remote file names (@pxref{Remote Files,, |
| 2558 | Remote Files, emacs, The GNU Emacs Manual}). |
| 2559 | |
| 2560 | To define a kind of magic file name, you must supply a regular |
| 2561 | expression to define the class of names (all those that match the |
| 2562 | regular expression), plus a handler that implements all the primitive |
| 2563 | Emacs file operations for file names that do match. |
| 2564 | |
| 2565 | @vindex file-name-handler-alist |
| 2566 | The variable @code{file-name-handler-alist} holds a list of handlers, |
| 2567 | together with regular expressions that determine when to apply each |
| 2568 | handler. Each element has this form: |
| 2569 | |
| 2570 | @example |
| 2571 | (@var{regexp} . @var{handler}) |
| 2572 | @end example |
| 2573 | |
| 2574 | @noindent |
| 2575 | All the Emacs primitives for file access and file name transformation |
| 2576 | check the given file name against @code{file-name-handler-alist}. If |
| 2577 | the file name matches @var{regexp}, the primitives handle that file by |
| 2578 | calling @var{handler}. |
| 2579 | |
| 2580 | The first argument given to @var{handler} is the name of the |
| 2581 | primitive, as a symbol; the remaining arguments are the arguments that |
| 2582 | were passed to that primitive. (The first of these arguments is most |
| 2583 | often the file name itself.) For example, if you do this: |
| 2584 | |
| 2585 | @example |
| 2586 | (file-exists-p @var{filename}) |
| 2587 | @end example |
| 2588 | |
| 2589 | @noindent |
| 2590 | and @var{filename} has handler @var{handler}, then @var{handler} is |
| 2591 | called like this: |
| 2592 | |
| 2593 | @example |
| 2594 | (funcall @var{handler} 'file-exists-p @var{filename}) |
| 2595 | @end example |
| 2596 | |
| 2597 | When a function takes two or more arguments that must be file names, |
| 2598 | it checks each of those names for a handler. For example, if you do |
| 2599 | this: |
| 2600 | |
| 2601 | @example |
| 2602 | (expand-file-name @var{filename} @var{dirname}) |
| 2603 | @end example |
| 2604 | |
| 2605 | @noindent |
| 2606 | then it checks for a handler for @var{filename} and then for a handler |
| 2607 | for @var{dirname}. In either case, the @var{handler} is called like |
| 2608 | this: |
| 2609 | |
| 2610 | @example |
| 2611 | (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname}) |
| 2612 | @end example |
| 2613 | |
| 2614 | @noindent |
| 2615 | The @var{handler} then needs to figure out whether to handle |
| 2616 | @var{filename} or @var{dirname}. |
| 2617 | |
| 2618 | If the specified file name matches more than one handler, the one |
| 2619 | whose match starts last in the file name gets precedence. This rule |
| 2620 | is chosen so that handlers for jobs such as uncompression are handled |
| 2621 | first, before handlers for jobs such as remote file access. |
| 2622 | |
| 2623 | Here are the operations that a magic file name handler gets to handle: |
| 2624 | |
| 2625 | @ifnottex |
| 2626 | @noindent |
| 2627 | @code{access-file}, @code{add-name-to-file}, |
| 2628 | @code{byte-compiler-base-file-name},@* |
| 2629 | @code{copy-directory}, @code{copy-file}, |
| 2630 | @code{delete-directory}, @code{delete-file}, |
| 2631 | @code{diff-latest-backup-file}, |
| 2632 | @code{directory-file-name}, |
| 2633 | @code{directory-files}, |
| 2634 | @code{directory-files-and-attributes}, |
| 2635 | @code{dired-compress-file}, @code{dired-uncache},@* |
| 2636 | @code{expand-file-name}, |
| 2637 | @code{file-accessible-directory-p}, |
| 2638 | @code{file-attributes}, |
| 2639 | @code{file-directory-p}, |
| 2640 | @code{file-executable-p}, @code{file-exists-p}, |
| 2641 | @code{file-local-copy}, @code{file-remote-p}, |
| 2642 | @code{file-modes}, @code{file-name-all-completions}, |
| 2643 | @code{file-name-as-directory}, |
| 2644 | @code{file-name-completion}, |
| 2645 | @code{file-name-directory}, |
| 2646 | @code{file-name-nondirectory}, |
| 2647 | @code{file-name-sans-versions}, @code{file-newer-than-file-p}, |
| 2648 | @code{file-ownership-preserved-p}, |
| 2649 | @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p}, |
| 2650 | @code{file-truename}, @code{file-writable-p}, |
| 2651 | @code{find-backup-file-name}, |
| 2652 | @c Not sure why it was here: @code{find-file-noselect},@* |
| 2653 | @code{get-file-buffer}, |
| 2654 | @code{insert-directory}, |
| 2655 | @code{insert-file-contents},@* |
| 2656 | @code{load}, |
| 2657 | @code{make-auto-save-file-name}, |
| 2658 | @code{make-directory}, |
| 2659 | @code{make-directory-internal}, |
| 2660 | @code{make-symbolic-link},@* |
| 2661 | @code{process-file}, |
| 2662 | @code{rename-file}, @code{set-file-modes}, @code{set-file-times}, |
| 2663 | @code{set-visited-file-modtime}, @code{shell-command}, |
| 2664 | @code{start-file-process}, |
| 2665 | @code{substitute-in-file-name},@* |
| 2666 | @code{unhandled-file-name-directory}, |
| 2667 | @code{vc-registered}, |
| 2668 | @code{verify-visited-file-modtime},@* |
| 2669 | @code{write-region}. |
| 2670 | @end ifnottex |
| 2671 | @iftex |
| 2672 | @noindent |
| 2673 | @flushleft |
| 2674 | @code{access-file}, @code{add-name-to-file}, |
| 2675 | @code{byte-com@discretionary{}{}{}piler-base-file-name}, |
| 2676 | @code{copy-directory}, @code{copy-file}, |
| 2677 | @code{delete-directory}, @code{delete-file}, |
| 2678 | @code{diff-latest-backup-file}, |
| 2679 | @code{directory-file-name}, |
| 2680 | @code{directory-files}, |
| 2681 | @code{directory-files-and-at@discretionary{}{}{}tributes}, |
| 2682 | @code{dired-compress-file}, @code{dired-uncache}, |
| 2683 | @code{expand-file-name}, |
| 2684 | @code{file-accessible-direc@discretionary{}{}{}tory-p}, |
| 2685 | @code{file-attributes}, |
| 2686 | @code{file-direct@discretionary{}{}{}ory-p}, |
| 2687 | @code{file-executable-p}, @code{file-exists-p}, |
| 2688 | @code{file-local-copy}, @code{file-remote-p}, |
| 2689 | @code{file-modes}, @code{file-name-all-completions}, |
| 2690 | @code{file-name-as-directory}, |
| 2691 | @code{file-name-completion}, |
| 2692 | @code{file-name-directory}, |
| 2693 | @code{file-name-nondirec@discretionary{}{}{}tory}, |
| 2694 | @code{file-name-sans-versions}, @code{file-newer-than-file-p}, |
| 2695 | @code{file-ownership-pre@discretionary{}{}{}served-p}, |
| 2696 | @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p}, |
| 2697 | @code{file-truename}, @code{file-writable-p}, |
| 2698 | @code{find-backup-file-name}, |
| 2699 | @c Not sure why it was here: @code{find-file-noselect}, |
| 2700 | @code{get-file-buffer}, |
| 2701 | @code{insert-directory}, |
| 2702 | @code{insert-file-contents}, |
| 2703 | @code{load}, @code{make-direc@discretionary{}{}{}tory}, |
| 2704 | @code{make-direc@discretionary{}{}{}tory-internal}, |
| 2705 | @code{make-symbolic-link}, |
| 2706 | @code{process-file}, |
| 2707 | @code{rename-file}, @code{set-file-modes}, |
| 2708 | @code{set-visited-file-modtime}, @code{shell-command}, |
| 2709 | @code{start-file-process}, |
| 2710 | @code{substitute-in-file-name}, |
| 2711 | @code{unhandled-file-name-directory}, |
| 2712 | @code{vc-regis@discretionary{}{}{}tered}, |
| 2713 | @code{verify-visited-file-modtime}, |
| 2714 | @code{write-region}. |
| 2715 | @end flushleft |
| 2716 | @end iftex |
| 2717 | |
| 2718 | Handlers for @code{insert-file-contents} typically need to clear the |
| 2719 | buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the |
| 2720 | @var{visit} argument is non-@code{nil}. This also has the effect of |
| 2721 | unlocking the buffer if it is locked. |
| 2722 | |
| 2723 | The handler function must handle all of the above operations, and |
| 2724 | possibly others to be added in the future. It need not implement all |
| 2725 | these operations itself---when it has nothing special to do for a |
| 2726 | certain operation, it can reinvoke the primitive, to handle the |
| 2727 | operation ``in the usual way.'' It should always reinvoke the primitive |
| 2728 | for an operation it does not recognize. Here's one way to do this: |
| 2729 | |
| 2730 | @smallexample |
| 2731 | (defun my-file-handler (operation &rest args) |
| 2732 | ;; @r{First check for the specific operations} |
| 2733 | ;; @r{that we have special handling for.} |
| 2734 | (cond ((eq operation 'insert-file-contents) @dots{}) |
| 2735 | ((eq operation 'write-region) @dots{}) |
| 2736 | @dots{} |
| 2737 | ;; @r{Handle any operation we don't know about.} |
| 2738 | (t (let ((inhibit-file-name-handlers |
| 2739 | (cons 'my-file-handler |
| 2740 | (and (eq inhibit-file-name-operation operation) |
| 2741 | inhibit-file-name-handlers))) |
| 2742 | (inhibit-file-name-operation operation)) |
| 2743 | (apply operation args))))) |
| 2744 | @end smallexample |
| 2745 | |
| 2746 | When a handler function decides to call the ordinary Emacs primitive for |
| 2747 | the operation at hand, it needs to prevent the primitive from calling |
| 2748 | the same handler once again, thus leading to an infinite recursion. The |
| 2749 | example above shows how to do this, with the variables |
| 2750 | @code{inhibit-file-name-handlers} and |
| 2751 | @code{inhibit-file-name-operation}. Be careful to use them exactly as |
| 2752 | shown above; the details are crucial for proper behavior in the case of |
| 2753 | multiple handlers, and for operations that have two file names that may |
| 2754 | each have handlers. |
| 2755 | |
| 2756 | @kindex safe-magic (@r{property}) |
| 2757 | Handlers that don't really do anything special for actual access to the |
| 2758 | file---such as the ones that implement completion of host names for |
| 2759 | remote file names---should have a non-@code{nil} @code{safe-magic} |
| 2760 | property. For instance, Emacs normally ``protects'' directory names |
| 2761 | it finds in @code{PATH} from becoming magic, if they look like magic |
| 2762 | file names, by prefixing them with @samp{/:}. But if the handler that |
| 2763 | would be used for them has a non-@code{nil} @code{safe-magic} |
| 2764 | property, the @samp{/:} is not added. |
| 2765 | |
| 2766 | @kindex operations (@r{property}) |
| 2767 | A file name handler can have an @code{operations} property to |
| 2768 | declare which operations it handles in a nontrivial way. If this |
| 2769 | property has a non-@code{nil} value, it should be a list of |
| 2770 | operations; then only those operations will call the handler. This |
| 2771 | avoids inefficiency, but its main purpose is for autoloaded handler |
| 2772 | functions, so that they won't be loaded except when they have real |
| 2773 | work to do. |
| 2774 | |
| 2775 | Simply deferring all operations to the usual primitives does not |
| 2776 | work. For instance, if the file name handler applies to |
| 2777 | @code{file-exists-p}, then it must handle @code{load} itself, because |
| 2778 | the usual @code{load} code won't work properly in that case. However, |
| 2779 | if the handler uses the @code{operations} property to say it doesn't |
| 2780 | handle @code{file-exists-p}, then it need not handle @code{load} |
| 2781 | nontrivially. |
| 2782 | |
| 2783 | @defvar inhibit-file-name-handlers |
| 2784 | This variable holds a list of handlers whose use is presently inhibited |
| 2785 | for a certain operation. |
| 2786 | @end defvar |
| 2787 | |
| 2788 | @defvar inhibit-file-name-operation |
| 2789 | The operation for which certain handlers are presently inhibited. |
| 2790 | @end defvar |
| 2791 | |
| 2792 | @defun find-file-name-handler file operation |
| 2793 | This function returns the handler function for file name @var{file}, |
| 2794 | or @code{nil} if there is none. The argument @var{operation} should |
| 2795 | be the operation to be performed on the file---the value you will pass |
| 2796 | to the handler as its first argument when you call it. If |
| 2797 | @var{operation} equals @code{inhibit-file-name-operation}, or if it is |
| 2798 | not found in the @code{operations} property of the handler, this |
| 2799 | function returns @code{nil}. |
| 2800 | @end defun |
| 2801 | |
| 2802 | @defun file-local-copy filename |
| 2803 | This function copies file @var{filename} to an ordinary non-magic file |
| 2804 | on the local machine, if it isn't on the local machine already. Magic |
| 2805 | file names should handle the @code{file-local-copy} operation if they |
| 2806 | refer to files on other machines. A magic file name that is used for |
| 2807 | other purposes than remote file access should not handle |
| 2808 | @code{file-local-copy}; then this function will treat the file as |
| 2809 | local. |
| 2810 | |
| 2811 | If @var{filename} is local, whether magic or not, this function does |
| 2812 | nothing and returns @code{nil}. Otherwise it returns the file name |
| 2813 | of the local copy file. |
| 2814 | @end defun |
| 2815 | |
| 2816 | @defun file-remote-p filename &optional identification connected |
| 2817 | This function tests whether @var{filename} is a remote file. If |
| 2818 | @var{filename} is local (not remote), the return value is @code{nil}. |
| 2819 | If @var{filename} is indeed remote, the return value is a string that |
| 2820 | identifies the remote system. |
| 2821 | |
| 2822 | This identifier string can include a host name and a user name, as |
| 2823 | well as characters designating the method used to access the remote |
| 2824 | system. For example, the remote identifier string for the filename |
| 2825 | @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}. |
| 2826 | |
| 2827 | If @code{file-remote-p} returns the same identifier for two different |
| 2828 | filenames, that means they are stored on the same file system and can |
| 2829 | be accessed locally with respect to each other. This means, for |
| 2830 | example, that it is possible to start a remote process accessing both |
| 2831 | files at the same time. Implementors of file handlers need to ensure |
| 2832 | this principle is valid. |
| 2833 | |
| 2834 | @var{identification} specifies which part of the identifier shall be |
| 2835 | returned as string. @var{identification} can be the symbol |
| 2836 | @code{method}, @code{user} or @code{host}; any other value is handled |
| 2837 | like @code{nil} and means to return the complete identifier string. |
| 2838 | In the example above, the remote @code{user} identifier string would |
| 2839 | be @code{root}. |
| 2840 | |
| 2841 | If @var{connected} is non-@code{nil}, this function returns @code{nil} |
| 2842 | even if @var{filename} is remote, if Emacs has no network connection |
| 2843 | to its host. This is useful when you want to avoid the delay of |
| 2844 | making connections when they don't exist. |
| 2845 | @end defun |
| 2846 | |
| 2847 | @defun unhandled-file-name-directory filename |
| 2848 | This function returns the name of a directory that is not magic. It |
| 2849 | uses the directory part of @var{filename} if that is not magic. For a |
| 2850 | magic file name, it invokes the file name handler, which therefore |
| 2851 | decides what value to return. If @var{filename} is not accessible |
| 2852 | from a local process, then the file name handler should indicate it by |
| 2853 | returning @code{nil}. |
| 2854 | |
| 2855 | This is useful for running a subprocess; every subprocess must have a |
| 2856 | non-magic directory to serve as its current directory, and this function |
| 2857 | is a good way to come up with one. |
| 2858 | @end defun |
| 2859 | |
| 2860 | @node Format Conversion |
| 2861 | @section File Format Conversion |
| 2862 | |
| 2863 | @cindex file format conversion |
| 2864 | @cindex encoding file formats |
| 2865 | @cindex decoding file formats |
| 2866 | @cindex text properties in files |
| 2867 | @cindex saving text properties |
| 2868 | Emacs performs several steps to convert the data in a buffer (text, |
| 2869 | text properties, and possibly other information) to and from a |
| 2870 | representation suitable for storing into a file. This section describes |
| 2871 | the fundamental functions that perform this @dfn{format conversion}, |
| 2872 | namely @code{insert-file-contents} for reading a file into a buffer, |
| 2873 | and @code{write-region} for writing a buffer into a file. |
| 2874 | |
| 2875 | @menu |
| 2876 | * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}. |
| 2877 | * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}. |
| 2878 | * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion. |
| 2879 | @end menu |
| 2880 | |
| 2881 | @node Format Conversion Overview |
| 2882 | @subsection Overview |
| 2883 | @noindent |
| 2884 | The function @code{insert-file-contents}: |
| 2885 | |
| 2886 | @itemize |
| 2887 | @item initially, inserts bytes from the file into the buffer; |
| 2888 | @item decodes bytes to characters as appropriate; |
| 2889 | @item processes formats as defined by entries in @code{format-alist}; and |
| 2890 | @item calls functions in @code{after-insert-file-functions}. |
| 2891 | @end itemize |
| 2892 | |
| 2893 | @noindent |
| 2894 | The function @code{write-region}: |
| 2895 | |
| 2896 | @itemize |
| 2897 | @item initially, calls functions in @code{write-region-annotate-functions}; |
| 2898 | @item processes formats as defined by entries in @code{format-alist}; |
| 2899 | @item encodes characters to bytes as appropriate; and |
| 2900 | @item modifies the file with the bytes. |
| 2901 | @end itemize |
| 2902 | |
| 2903 | This shows the symmetry of the lowest-level operations; reading and |
| 2904 | writing handle things in opposite order. The rest of this section |
| 2905 | describes the two facilities surrounding the three variables named |
| 2906 | above, as well as some related functions. @ref{Coding Systems}, for |
| 2907 | details on character encoding and decoding. |
| 2908 | |
| 2909 | @node Format Conversion Round-Trip |
| 2910 | @subsection Round-Trip Specification |
| 2911 | |
| 2912 | The most general of the two facilities is controlled by the variable |
| 2913 | @code{format-alist}, a list of @dfn{file format} specifications, which |
| 2914 | describe textual representations used in files for the data in an Emacs |
| 2915 | buffer. The descriptions for reading and writing are paired, which is |
| 2916 | why we call this ``round-trip'' specification |
| 2917 | (@pxref{Format Conversion Piecemeal}, for non-paired specification). |
| 2918 | |
| 2919 | @defvar format-alist |
| 2920 | This list contains one format definition for each defined file format. |
| 2921 | Each format definition is a list of this form: |
| 2922 | |
| 2923 | @example |
| 2924 | (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve}) |
| 2925 | @end example |
| 2926 | @end defvar |
| 2927 | |
| 2928 | @cindex format definition |
| 2929 | @noindent |
| 2930 | Here is what the elements in a format definition mean: |
| 2931 | |
| 2932 | @table @var |
| 2933 | @item name |
| 2934 | The name of this format. |
| 2935 | |
| 2936 | @item doc-string |
| 2937 | A documentation string for the format. |
| 2938 | |
| 2939 | @item regexp |
| 2940 | A regular expression which is used to recognize files represented in |
| 2941 | this format. If @code{nil}, the format is never applied automatically. |
| 2942 | |
| 2943 | @item from-fn |
| 2944 | A shell command or function to decode data in this format (to convert |
| 2945 | file data into the usual Emacs data representation). |
| 2946 | |
| 2947 | A shell command is represented as a string; Emacs runs the command as a |
| 2948 | filter to perform the conversion. |
| 2949 | |
| 2950 | If @var{from-fn} is a function, it is called with two arguments, @var{begin} |
| 2951 | and @var{end}, which specify the part of the buffer it should convert. |
| 2952 | It should convert the text by editing it in place. Since this can |
| 2953 | change the length of the text, @var{from-fn} should return the modified |
| 2954 | end position. |
| 2955 | |
| 2956 | One responsibility of @var{from-fn} is to make sure that the beginning |
| 2957 | of the file no longer matches @var{regexp}. Otherwise it is likely to |
| 2958 | get called again. |
| 2959 | |
| 2960 | @item to-fn |
| 2961 | A shell command or function to encode data in this format---that is, to |
| 2962 | convert the usual Emacs data representation into this format. |
| 2963 | |
| 2964 | If @var{to-fn} is a string, it is a shell command; Emacs runs the |
| 2965 | command as a filter to perform the conversion. |
| 2966 | |
| 2967 | If @var{to-fn} is a function, it is called with three arguments: |
| 2968 | @var{begin} and @var{end}, which specify the part of the buffer it |
| 2969 | should convert, and @var{buffer}, which specifies which buffer. There |
| 2970 | are two ways it can do the conversion: |
| 2971 | |
| 2972 | @itemize @bullet |
| 2973 | @item |
| 2974 | By editing the buffer in place. In this case, @var{to-fn} should |
| 2975 | return the end-position of the range of text, as modified. |
| 2976 | |
| 2977 | @item |
| 2978 | By returning a list of annotations. This is a list of elements of the |
| 2979 | form @code{(@var{position} . @var{string})}, where @var{position} is an |
| 2980 | integer specifying the relative position in the text to be written, and |
| 2981 | @var{string} is the annotation to add there. The list must be sorted in |
| 2982 | order of position when @var{to-fn} returns it. |
| 2983 | |
| 2984 | When @code{write-region} actually writes the text from the buffer to the |
| 2985 | file, it intermixes the specified annotations at the corresponding |
| 2986 | positions. All this takes place without modifying the buffer. |
| 2987 | @end itemize |
| 2988 | |
| 2989 | @item modify |
| 2990 | A flag, @code{t} if the encoding function modifies the buffer, and |
| 2991 | @code{nil} if it works by returning a list of annotations. |
| 2992 | |
| 2993 | @item mode-fn |
| 2994 | A minor-mode function to call after visiting a file converted from this |
| 2995 | format. The function is called with one argument, the integer 1; |
| 2996 | that tells a minor-mode function to enable the mode. |
| 2997 | |
| 2998 | @item preserve |
| 2999 | A flag, @code{t} if @code{format-write-file} should not remove this format |
| 3000 | from @code{buffer-file-format}. |
| 3001 | @end table |
| 3002 | |
| 3003 | The function @code{insert-file-contents} automatically recognizes file |
| 3004 | formats when it reads the specified file. It checks the text of the |
| 3005 | beginning of the file against the regular expressions of the format |
| 3006 | definitions, and if it finds a match, it calls the decoding function for |
| 3007 | that format. Then it checks all the known formats over again. |
| 3008 | It keeps checking them until none of them is applicable. |
| 3009 | |
| 3010 | Visiting a file, with @code{find-file-noselect} or the commands that use |
| 3011 | it, performs conversion likewise (because it calls |
| 3012 | @code{insert-file-contents}); it also calls the mode function for each |
| 3013 | format that it decodes. It stores a list of the format names in the |
| 3014 | buffer-local variable @code{buffer-file-format}. |
| 3015 | |
| 3016 | @defvar buffer-file-format |
| 3017 | This variable states the format of the visited file. More precisely, |
| 3018 | this is a list of the file format names that were decoded in the course |
| 3019 | of visiting the current buffer's file. It is always buffer-local in all |
| 3020 | buffers. |
| 3021 | @end defvar |
| 3022 | |
| 3023 | When @code{write-region} writes data into a file, it first calls the |
| 3024 | encoding functions for the formats listed in @code{buffer-file-format}, |
| 3025 | in the order of appearance in the list. |
| 3026 | |
| 3027 | @deffn Command format-write-file file format &optional confirm |
| 3028 | This command writes the current buffer contents into the file @var{file} |
| 3029 | in a format based on @var{format}, which is a list of format names. It |
| 3030 | constructs the actual format starting from @var{format}, then appending |
| 3031 | any elements from the value of @code{buffer-file-format} with a non-nil |
| 3032 | @var{preserve} flag (see above), if they are not already present in |
| 3033 | @var{format}. It then updates @code{buffer-file-format} with this |
| 3034 | format, making it the default for future saves. Except for the |
| 3035 | @var{format} argument, this command is similar to @code{write-file}. In |
| 3036 | particular, @var{confirm} has the same meaning and interactive treatment |
| 3037 | as the corresponding argument to @code{write-file}. @xref{Definition of |
| 3038 | write-file}. |
| 3039 | @end deffn |
| 3040 | |
| 3041 | @deffn Command format-find-file file format |
| 3042 | This command finds the file @var{file}, converting it according to |
| 3043 | format @var{format}. It also makes @var{format} the default if the |
| 3044 | buffer is saved later. |
| 3045 | |
| 3046 | The argument @var{format} is a list of format names. If @var{format} is |
| 3047 | @code{nil}, no conversion takes place. Interactively, typing just |
| 3048 | @key{RET} for @var{format} specifies @code{nil}. |
| 3049 | @end deffn |
| 3050 | |
| 3051 | @deffn Command format-insert-file file format &optional beg end |
| 3052 | This command inserts the contents of file @var{file}, converting it |
| 3053 | according to format @var{format}. If @var{beg} and @var{end} are |
| 3054 | non-@code{nil}, they specify which part of the file to read, as in |
| 3055 | @code{insert-file-contents} (@pxref{Reading from Files}). |
| 3056 | |
| 3057 | The return value is like what @code{insert-file-contents} returns: a |
| 3058 | list of the absolute file name and the length of the data inserted |
| 3059 | (after conversion). |
| 3060 | |
| 3061 | The argument @var{format} is a list of format names. If @var{format} is |
| 3062 | @code{nil}, no conversion takes place. Interactively, typing just |
| 3063 | @key{RET} for @var{format} specifies @code{nil}. |
| 3064 | @end deffn |
| 3065 | |
| 3066 | @defvar buffer-auto-save-file-format |
| 3067 | This variable specifies the format to use for auto-saving. Its value is |
| 3068 | a list of format names, just like the value of |
| 3069 | @code{buffer-file-format}; however, it is used instead of |
| 3070 | @code{buffer-file-format} for writing auto-save files. If the value |
| 3071 | is @code{t}, the default, auto-saving uses the same format as a |
| 3072 | regular save in the same buffer. This variable is always buffer-local |
| 3073 | in all buffers. |
| 3074 | @end defvar |
| 3075 | |
| 3076 | @node Format Conversion Piecemeal |
| 3077 | @subsection Piecemeal Specification |
| 3078 | |
| 3079 | In contrast to the round-trip specification described in the previous |
| 3080 | subsection (@pxref{Format Conversion Round-Trip}), you can use the variables |
| 3081 | @code{after-insert-file-functions} and @code{write-region-annotate-functions} |
| 3082 | to separately control the respective reading and writing conversions. |
| 3083 | |
| 3084 | Conversion starts with one representation and produces another |
| 3085 | representation. When there is only one conversion to do, there is no |
| 3086 | conflict about what to start with. However, when there are multiple |
| 3087 | conversions involved, conflict may arise when two conversions need to |
| 3088 | start with the same data. |
| 3089 | |
| 3090 | This situation is best understood in the context of converting text |
| 3091 | properties during @code{write-region}. For example, the character at |
| 3092 | position 42 in a buffer is @samp{X} with a text property @code{foo}. If |
| 3093 | the conversion for @code{foo} is done by inserting into the buffer, say, |
| 3094 | @samp{FOO:}, then that changes the character at position 42 from |
| 3095 | @samp{X} to @samp{F}. The next conversion will start with the wrong |
| 3096 | data straight away. |
| 3097 | |
| 3098 | To avoid conflict, cooperative conversions do not modify the buffer, |
| 3099 | but instead specify @dfn{annotations}, a list of elements of the form |
| 3100 | @code{(@var{position} . @var{string})}, sorted in order of increasing |
| 3101 | @var{position}. |
| 3102 | |
| 3103 | If there is more than one conversion, @code{write-region} merges their |
| 3104 | annotations destructively into one sorted list. Later, when the text |
| 3105 | from the buffer is actually written to the file, it intermixes the |
| 3106 | specified annotations at the corresponding positions. All this takes |
| 3107 | place without modifying the buffer. |
| 3108 | |
| 3109 | @c ??? What about ``overriding'' conversions like those allowed |
| 3110 | @c ??? for `write-region-annotate-functions', below? --ttn |
| 3111 | |
| 3112 | In contrast, when reading, the annotations intermixed with the text |
| 3113 | are handled immediately. @code{insert-file-contents} sets point to |
| 3114 | the beginning of some text to be converted, then calls the conversion |
| 3115 | functions with the length of that text. These functions should always |
| 3116 | return with point at the beginning of the inserted text. This |
| 3117 | approach makes sense for reading because annotations removed by the |
| 3118 | first converter can't be mistakenly processed by a later converter. |
| 3119 | Each conversion function should scan for the annotations it |
| 3120 | recognizes, remove the annotation, modify the buffer text (to set a |
| 3121 | text property, for example), and return the updated length of the |
| 3122 | text, as it stands after those changes. The value returned by one |
| 3123 | function becomes the argument to the next function. |
| 3124 | |
| 3125 | @defvar write-region-annotate-functions |
| 3126 | A list of functions for @code{write-region} to call. Each function in |
| 3127 | the list is called with two arguments: the start and end of the region |
| 3128 | to be written. These functions should not alter the contents of the |
| 3129 | buffer. Instead, they should return annotations. |
| 3130 | |
| 3131 | As a special case, a function may return with a different buffer |
| 3132 | current. Emacs takes this to mean that the current buffer contains |
| 3133 | altered text to be output. It therefore changes the @var{start} and |
| 3134 | @var{end} arguments of the @code{write-region} call, giving them the |
| 3135 | values of @code{point-min} and @code{point-max} in the new buffer, |
| 3136 | respectively. It also discards all previous annotations, because they |
| 3137 | should have been dealt with by this function. |
| 3138 | @end defvar |
| 3139 | |
| 3140 | @defvar write-region-post-annotation-function |
| 3141 | The value of this variable, if non-@code{nil}, should be a function. |
| 3142 | This function is called, with no arguments, after @code{write-region} |
| 3143 | has completed. |
| 3144 | |
| 3145 | If any function in @code{write-region-annotate-functions} returns with |
| 3146 | a different buffer current, Emacs calls |
| 3147 | @code{write-region-post-annotation-function} more than once. Emacs |
| 3148 | calls it with the last buffer that was current, and again with the |
| 3149 | buffer before that, and so on back to the original buffer. |
| 3150 | |
| 3151 | Thus, a function in @code{write-region-annotate-functions} can create |
| 3152 | a buffer, give this variable the local value of @code{kill-buffer} in |
| 3153 | that buffer, set up the buffer with altered text, and make the buffer |
| 3154 | current. The buffer will be killed after @code{write-region} is done. |
| 3155 | @end defvar |
| 3156 | |
| 3157 | @defvar after-insert-file-functions |
| 3158 | Each function in this list is called by @code{insert-file-contents} |
| 3159 | with one argument, the number of characters inserted, and with point |
| 3160 | at the beginning of the inserted text. Each function should leave |
| 3161 | point unchanged, and return the new character count describing the |
| 3162 | inserted text as modified by the function. |
| 3163 | @c ??? The docstring mentions a handler from `file-name-handler-alist' |
| 3164 | @c "intercepting" `insert-file-contents'. Hmmm. --ttn |
| 3165 | @end defvar |
| 3166 | |
| 3167 | We invite users to write Lisp programs to store and retrieve text |
| 3168 | properties in files, using these hooks, and thus to experiment with |
| 3169 | various data formats and find good ones. Eventually we hope users |
| 3170 | will produce good, general extensions we can install in Emacs. |
| 3171 | |
| 3172 | We suggest not trying to handle arbitrary Lisp objects as text property |
| 3173 | names or values---because a program that general is probably difficult |
| 3174 | to write, and slow. Instead, choose a set of possible data types that |
| 3175 | are reasonably flexible, and not too hard to encode. |
| 3176 | |
| 3177 | @ignore |
| 3178 | arch-tag: 141f74ce-6ae3-40dc-a6c4-ef83fc4ec35c |
| 3179 | @end ignore |