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This is Info file ../../info/xemacs.info, produced by Makeinfo version 1.68 from the input file xemacs.texi. This file documents the XEmacs editor. Copyright (C) 1985, 1986, 1988 Richard M. Stallman. Copyright (C) 1991, 1992, 1993, 1994 Lucid, Inc. Copyright (C) 1993, 1994 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "The GNU Manifesto", "Distribution" and "GNU General Public License" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "The GNU Manifesto", "Distribution" and "GNU General Public License" may be included in a translation approved by the author instead of in the original English. File: xemacs.info, Node: Search Case, Next: Replace, Prev: Regexps, Up: Search Searching and Case ================== All searches in Emacs normally ignore the case of the text they are searching through; if you specify searching for `FOO', `Foo' and `foo' are also considered a match. Regexps, and in particular character sets, are included: `[aB]' matches `a' or `A' or `b' or `B'. If you want a case-sensitive search, set the variable `case-fold-search' to `nil'. Then all letters must match exactly, including case. `case-fold-search' is a per-buffer variable; altering it affects only the current buffer, but there is a default value which you can change as well. *Note Locals::. You can also use Case Sensitive Search from the Options menu on your screen. File: xemacs.info, Node: Replace, Next: Other Repeating Search, Prev: Search Case, Up: Search Replacement Commands ==================== Global search-and-replace operations are not needed as often in Emacs as they are in other editors, but they are available. In addition to the simple `replace-string' command which is like that found in most editors, there is a `query-replace' command which asks you, for each occurrence of a pattern, whether to replace it. The replace commands all replace one string (or regexp) with one replacement string. It is possible to perform several replacements in parallel using the command `expand-region-abbrevs'. *Note Expanding Abbrevs::. * Menu: * Unconditional Replace:: Replacing all matches for a string. * Regexp Replace:: Replacing all matches for a regexp. * Replacement and Case:: How replacements preserve case of letters. * Query Replace:: How to use querying. File: xemacs.info, Node: Unconditional Replace, Next: Regexp Replace, Prev: Replace, Up: Replace Unconditional Replacement ------------------------- `M-x replace-string <RET> STRING <RET> NEWSTRING <RET>' Replace every occurrence of STRING with NEWSTRING. `M-x replace-regexp <RET> REGEXP <RET> NEWSTRING <RET>' Replace every match for REGEXP with NEWSTRING. To replace every instance of `foo' after point with `bar', use the command `M-x replace-string' with the two arguments `foo' and `bar'. Replacement occurs only after point: if you want to cover the whole buffer you must go to the beginning first. By default, all occurrences up to the end of the buffer are replaced. To limit replacement to part of the buffer, narrow to that part of the buffer before doing the replacement (*note Narrowing::.). When `replace-string' exits, point is left at the last occurrence replaced. The value of point when the `replace-string' command was issued is remembered on the mark ring; `C-u C-<SPC>' moves back there. A numeric argument restricts replacement to matches that are surrounded by word boundaries. File: xemacs.info, Node: Regexp Replace, Next: Replacement and Case, Prev: Unconditional Replace, Up: Replace Regexp Replacement ------------------ `replace-string' replaces exact matches for a single string. The similar command `replace-regexp' replaces any match for a specified pattern. In `replace-regexp', the NEWSTRING need not be constant. It can refer to all or part of what is matched by the REGEXP. `\&' in NEWSTRING stands for the entire text being replaced. `\D' in NEWSTRING, where D is a digit, stands for whatever matched the D'th parenthesized grouping in REGEXP. For example, M-x replace-regexp <RET> c[ad]+r <RET> \&-safe <RET> would replace (for example) `cadr' with `cadr-safe' and `cddr' with `cddr-safe'. M-x replace-regexp <RET> $c[ad]+r$-safe <RET> \1 <RET> would perform exactly the opposite replacements. To include a `\' in the text to replace with, you must give `\\'. File: xemacs.info, Node: Replacement and Case, Next: Query Replace, Prev: Regexp Replace, Up: Replace Replace Commands and Case ------------------------- If the arguments to a replace command are in lower case, the command preserves case when it makes a replacement. Thus, the following command: M-x replace-string <RET> foo <RET> bar <RET> replaces a lower-case `foo' with a lower case `bar', `FOO' with `BAR', and `Foo' with `Bar'. If upper-case letters are used in the second argument, they remain upper-case every time that argument is inserted. If upper-case letters are used in the first argument, the second argument is always substituted exactly as given, with no case conversion. Likewise, if the variable `case-replace' is set to `nil', replacement is done without case conversion. If `case-fold-search' is set to `nil', case is significant in matching occurrences of `foo' to replace; also, case conversion of the replacement string is not done. File: xemacs.info, Node: Query Replace, Prev: Replacement and Case, Up: Replace Query Replace ------------- `M-% STRING <RET> NEWSTRING <RET>' `M-x query-replace <RET> STRING <RET> NEWSTRING <RET>' Replace some occurrences of STRING with NEWSTRING. `M-x query-replace-regexp <RET> REGEXP <RET> NEWSTRING <RET>' Replace some matches for REGEXP with NEWSTRING. If you want to change only some of the occurrences of `foo' to `bar', not all of them, you can use `query-replace' instead of `M-%'. This command finds occurrences of `foo' one by one, displays each occurrence, and asks you whether to replace it. A numeric argument to `query-replace' tells it to consider only occurrences that are bounded by word-delimiter characters. Aside from querying, `query-replace' works just like `replace-string', and `query-replace-regexp' works just like `replace-regexp'. The things you can type when you are shown an occurrence of STRING or a match for REGEXP are: `<SPC>' to replace the occurrence with NEWSTRING. This preserves case, just like `replace-string', provided `case-replace' is non-`nil', as it normally is. `<DEL>' to skip to the next occurrence without replacing this one. `, (Comma)' to replace this occurrence and display the result. You are then prompted for another input character. However, since the replacement has already been made, <DEL> and <SPC> are equivalent. At this point, you can type `C-r' (see below) to alter the replaced text. To undo the replacement, you can type `C-x u'. This exits the `query-replace'. If you want to do further replacement you must use `C-x ESC' to restart (*note Repetition::.). `<ESC>' to exit without doing any more replacements. `. (Period)' to replace this occurrence and then exit. `!' to replace all remaining occurrences without asking again. `^' to go back to the location of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake. This works by popping the mark ring. Only one `^' in a row is allowed, because only one previous replacement location is kept during `query-replace'. `C-r' to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with NEWSTRING. When you are done, exit the recursive editing level with `C-M-c' and the next occurrence will be displayed. *Note Recursive Edit::. `C-w' to delete the occurrence, and then enter a recursive editing level as in `C-r'. Use the recursive edit to insert text to replace the deleted occurrence of STRING. When done, exit the recursive editing level with `C-M-c' and the next occurrence will be displayed. `C-l' to redisplay the screen and then give another answer. `C-h' to display a message summarizing these options, then give another answer. If you type any other character, Emacs exits the `query-replace', and executes the character as a command. To restart the `query-replace', use `C-x <ESC>', which repeats the `query-replace' because it used the minibuffer to read its arguments. *Note C-x ESC: Repetition. File: xemacs.info, Node: Other Repeating Search, Prev: Replace, Up: Search Other Search-and-Loop Commands ============================== Here are some other commands that find matches for a regular expression. They all operate from point to the end of the buffer. `M-x occur' Print each line that follows point and contains a match for the specified regexp. A numeric argument specifies the number of context lines to print before and after each matching line; the default is none. The buffer `*Occur*' containing the output serves as a menu for finding occurrences in their original context. Find an occurrence as listed in `*Occur*', position point there, and type `C-c C-c'; this switches to the buffer that was searched and moves point to the original of the same occurrence. `M-x list-matching-lines' Synonym for `M-x occur'. `M-x count-matches' Print the number of matches following point for the specified regexp. `M-x delete-non-matching-lines' Delete each line that follows point and does not contain a match for the specified regexp. `M-x delete-matching-lines' Delete each line that follows point and contains a match for the specified regexp. File: xemacs.info, Node: Fixit, Next: Files, Prev: Search, Up: Top Commands for Fixing Typos ************************* This chapter describes commands that are especially useful when you catch a mistake in your text just after you have made it, or when you change your mind while composing text on line. * Menu: * Kill Errors:: Commands to kill a batch of recently entered text. * Transpose:: Exchanging two characters, words, lines, lists... * Fixing Case:: Correcting case of last word entered. * Spelling:: Apply spelling checker to a word, or a whole file. File: xemacs.info, Node: Kill Errors, Next: Transpose, Prev: Fixit, Up: Fixit Killing Your Mistakes ===================== `<DEL>' Delete last character (`delete-backward-char'). `M-<DEL>' Kill last word (`backward-kill-word'). `C-x <DEL>' Kill to beginning of sentence (`backward-kill-sentence'). The <DEL> character (`delete-backward-char') is the most important correction command. When used among graphic (self-inserting) characters, it can be thought of as canceling the last character typed. When your mistake is longer than a couple of characters, it might be more convenient to use `M-<DEL>' or `C-x <DEL>'. `M-<DEL>' kills back to the start of the last word, and `C-x <DEL>' kills back to the start of the last sentence. `C-x <DEL>' is particularly useful when you are thinking of what to write as you type it, in case you change your mind about phrasing. `M-<DEL>' and `C-x <DEL>' save the killed text for `C-y' and `M-y' to retrieve. *Note Yanking::. `M-<DEL>' is often useful even when you have typed only a few characters wrong, if you know you are confused in your typing and aren't sure exactly what you typed. At such a time, you cannot correct with <DEL> except by looking at the screen to see what you did. It requires less thought to kill the whole word and start over. File: xemacs.info, Node: Transpose, Next: Fixing Case, Prev: Kill Errors, Up: Fixit Transposing Text ================ `C-t' Transpose two characters (`transpose-chars'). `M-t' Transpose two words (`transpose-words'). `C-M-t' Transpose two balanced expressions (`transpose-sexps'). `C-x C-t' Transpose two lines (`transpose-lines'). The common error of transposing two adjacent characters can be fixed with the `C-t' command (`transpose-chars'). Normally, `C-t' transposes the two characters on either side of point. When given at the end of a line, `C-t' transposes the last two characters on the line, rather than transposing the last character of the line with the newline, which would be useless. If you catch a transposition error right away, you can fix it with just `C-t'. If you catch the error later, move the cursor back to between the two transposed characters. If you transposed a space with the last character of the word before it, the word motion commands are a good way of getting there. Otherwise, a reverse search (`C-r') is often the best way. *Note Search::. `Meta-t' (`transpose-words') transposes the word before point with the word after point. It moves point forward over a word, dragging the word preceding or containing point forward as well. The punctuation characters between the words do not move. For example, `FOO, BAR' transposes into `BAR, FOO' rather than `BAR FOO,'. `C-M-t' (`transpose-sexps') is a similar command for transposing two expressions (*note Lists::.), and `C-x C-t' (`transpose-lines') exchanges lines. It works like `M-t' but in determines the division of the text into syntactic units differently. A numeric argument to a transpose command serves as a repeat count: it tells the transpose command to move the character (word, sexp, line) before or containing point across several other characters (words, sexps, lines). For example, `C-u 3 C-t' moves the character before point forward across three other characters. This is equivalent to repeating `C-t' three times. `C-u - 4 M-t' moves the word before point backward across four words. `C-u - C-M-t' would cancel the effect of plain `C-M-t'. A numeric argument of zero transposes the character (word, sexp, line) ending after point with the one ending after the mark (otherwise a command with a repeat count of zero would do nothing). File: xemacs.info, Node: Fixing Case, Next: Spelling, Prev: Transpose, Up: Fixit Case Conversion =============== `M-- M-l' Convert last word to lower case. Note that `Meta--' is "Meta-minus." `M-- M-u' Convert last word to all upper case. `M-- M-c' Convert last word to lower case with capital initial. A common error is to type words in the wrong case. Because of this, the word case-conversion commands `M-l', `M-u', and `M-c' do not move the cursor when used with a negative argument. As soon as you see you have mistyped the last word, you can simply case-convert it and continue typing. *Note Case::. File: xemacs.info, Node: Spelling, Prev: Fixing Case, Up: Fixit Checking and Correcting Spelling ================================ `M-$' Check and correct spelling of word (`spell-word'). `M-x spell-buffer' Check and correct spelling of each word in the buffer. `M-x spell-region' Check and correct spelling of each word in the region. `M-x spell-string' Check spelling of specified word. To check the spelling of the word before point, and optionally correct it, use the command `M-$' (`spell-word'). This command runs an inferior process containing the `spell' program to see whether the word is correct English. If it is not, it asks you to edit the word (in the minibuffer) into a corrected spelling, and then performs a `query-replace' to substitute the corrected spelling for the old one throughout the buffer. If you exit the minibuffer without altering the original spelling, it means you do not want to do anything to that word. In that case, the `query-replace' is not done. `M-x spell-buffer' checks each word in the buffer the same way that `spell-word' does, doing a `query-replace' for every incorrect word if appropriate. `M-x spell-region' is similar to `spell-buffer' but operates only on the region, not the entire buffer. `M-x spell-string' reads a string as an argument and checks whether that is a correctly spelled English word. It prints a message giving the answer in the echo area. File: xemacs.info, Node: Files, Next: Buffers, Prev: Fixit, Up: Top File Handling ************* The basic unit of stored data in Unix is the "file". To edit a file, you must tell Emacs to examine the file and prepare a buffer containing a copy of the file's text. This is called "visiting" the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you "save" the buffer back into the file. In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, and operate on file directories. * Menu: * File Names:: How to type and edit file name arguments. * Visiting:: Visiting a file prepares Emacs to edit the file. * Saving:: Saving makes your changes permanent. * Reverting:: Reverting cancels all the changes not saved. * Auto Save:: Auto Save periodically protects against loss of data. * Version Control:: Version control systems (RCS and SCCS). * ListDir:: Listing the contents of a file directory. * Comparing Files:: Finding where two files differ. * Dired:: "Editing" a directory to delete, rename, etc. the files in it. * Misc File Ops:: Other things you can do on files. File: xemacs.info, Node: File Names, Next: Visiting, Prev: Files, Up: Files File Names ========== Most Emacs commands that operate on a file require you to specify the file name. (Saving and reverting are exceptions; the buffer knows which file name to use for them.) File names are specified in the minibuffer (*note Minibuffer::.). "Completion" is available, to make it easier to specify long file names. *Note Completion::. There is always a "default file name" which is used if you enter an empty argument by typing just <RET>. Normally the default file name is the name of the file visited in the current buffer; this makes it easy to operate on that file with any of the Emacs file commands. Each buffer has a default directory, normally the same as the directory of the file visited in that buffer. When Emacs reads a file name, the default directory is used if you do not specify a directory. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory. The default directory of the current buffer is kept in the variable `default-directory', which has a separate value in every buffer. The value of the variable should end with a slash. For example, if the default file name is `/u/rms/gnu/gnu.tasks' then the default directory is `/u/rms/gnu/'. If you type just `foo', which does not specify a directory, it is short for `/u/rms/gnu/foo'. `../.login' would stand for `/u/rms/.login'. `new/foo' would stand for the filename `/u/rms/gnu/new/foo'. The variable `default-directory-alist' takes an alist of major modes and their opinions on `default-directory' as a Lisp expression to evaluate. A resulting value of `nil' is ignored in favor of `default-directory'. You can create a new directory with the function `make-directory', which takes as an argument a file name string. The current directory is displayed in the minibuffer when the function is called; you can delete the old directory name and supply a new directory name. For example, if the current directory is `/u/rms/gnu', you can delete `gnu' and type `oryx' and <RET> to create `/u/rms/oryx'. Removing a directory is similar to creating one. To remove a directory, use `remove-directory'; it takes one argument, a file name string. The command `M-x pwd' prints the current buffer's default directory, and the command `M-x cd' sets it (to a value read using the minibuffer). A buffer's default directory changes only when the `cd' command is used. A file-visiting buffer's default directory is initialized to the directory of the file that is visited there. If a buffer is created with `C-x b', its default directory is copied from that of the buffer that was current at the time. The default directory name actually appears in the minibuffer when the minibuffer becomes active to read a file name. This serves two purposes: it shows you what the default is, so that you can type a relative file name and know with certainty what it will mean, and it allows you to edit the default to specify a different directory. To inhibit the insertion of the default directory, set the variable `insert-default-directory' to `nil'. Note that it is legitimate to type an absolute file name after you enter the minibuffer, ignoring the presence of the default directory name. The final minibuffer contents may look invalid, but that is not so. *Note Minibuffer File::. `$' in a file name is used to substitute environment variables. For example, if you have used the shell command `setenv FOO rms/hacks' to set up an environment variable named `FOO', then you can use `/u/$FOO/test.c' or `/u/${FOO}/test.c' as an abbreviation for `/u/rms/hacks/test.c'. The environment variable name consists of all the alphanumeric characters after the `$'; alternatively, it may be enclosed in braces after the `$'. Note that the `setenv' command affects Emacs only if done before Emacs is started. To access a file with `$' in its name, type `$$'. This pair is converted to a single `$' at the same time variable substitution is performed for single `$'. The Lisp function that performs the substitution is called `substitute-in-file-name'. The substitution is performed only on filenames read as such using the minibuffer. File: xemacs.info, Node: Visiting, Next: Saving, Prev: File Names, Up: Files Visiting Files ============== `C-x C-f' Visit a file (`find-file'). `C-x C-v' Visit a different file instead of the one visited last (`find-alternate-file'). `C-x 4 C-f' Visit a file, in another window (`find-file-other-window'). Don't change this window. `C-x 5 C-f' Visit a file, in another frame (`find-file-other-frame'). Don't change this window or frame. "Visiting" a file means copying its contents into an Emacs buffer so you can edit it. Emacs creates a new buffer for each file you visit. We say that the buffer is visiting the file that it was created to hold. Emacs constructs the buffer name from the file name by throwing away the directory and keeping just the file name. For example, a file named `/usr/rms/emacs.tex' is displayed in a buffer named `emacs.tex'. If a buffer with that name exists, a unique name is constructed by appending `<2>', `<3>',and so on, using the lowest number that makes a name that is not already in use. Each window's mode line shows the name of the buffer that is being displayed in that window, so you can always tell what buffer you are editing. The changes you make with Emacs are made in the Emacs buffer. They do not take effect in the file that you visit, or any other permanent place, until you "save" the buffer. Saving the buffer means that Emacs writes the current contents of the buffer into its visited file. *Note Saving::. If a buffer contains changes that have not been saved, the buffer is said to be "modified". This is important because it implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin if the buffer is modified. To visit a file, use the command `C-x C-f' (`find-file'). Follow the command with the name of the file you wish to visit, terminated by a <RET>. If you are using XEmacs under X, you can also use the Open... command from the File menu bar item. The file name is read using the minibuffer (*note Minibuffer::.), with defaulting and completion in the standard manner (*note File Names::.). While in the minibuffer, you can abort `C-x C-f' by typing `C-g'. `C-x C-f' has completed successfully when text appears on the screen and a new buffer name appears in the mode line. If the specified file does not exist and could not be created or cannot be read, an error results. The error message is printed in the echo area, and includes the name of the file that Emacs was trying to visit. If you visit a file that is already in Emacs, `C-x C-f' does not make another copy. It selects the existing buffer containing that file. However, before doing so, it checks that the file itself has not changed since you visited or saved it last. If the file has changed, Emacs prints a warning message. *Note Simultaneous Editing: Interlocking. You can switch to a specific file called out in the current buffer by calling the function `find-this-file'. By providing a prefix argument, this function calls `filename-at-point' and switches to a buffer visiting the file FILENAME. It creates one if none already exists. You can use this function to edit the file mentioned in the buffer you are working in or to test if the file exists. You can do that by using the minibuffer completion after snatching the all or part of the filename. If the variable `find-file-use-truenames''s value is non-`nil', a buffer's visited filename will always be traced back to the real file. The filename will never be a symbolic link, and there will never be a symbolic link anywhere in its directory path. In other words, the `buffer-file-name' and `buffer-file-truename' will be equal. If the variable `find-file-compare-truenames' value is non-`nil', the `find-file' command will check the `buffer-file-truename' of all visited files when deciding whether a given file is already in a buffer, instead of just `buffer-file-name'. If you attempt to visit another file which is a hard-link or symbolic-link to a file that is already in a buffer, the existing buffer will be found instead of a newly created one. If you want to create a file, just visit it. Emacs prints `(New File)' in the echo area, but in other respects behaves as if you had visited an existing empty file. If you make any changes and save them, the file is created. If you visit a nonexistent file unintentionally (because you typed the wrong file name), use the `C-x C-v' (`find-alternate-file') command to visit the file you wanted. `C-x C-v' is similar to `C-x C-f', but it kills the current buffer (after first offering to save it if it is modified). `C-x C-v' is allowed even if the current buffer is not visiting a file. If the file you specify is actually a directory, Dired is called on that directory (*note Dired::.). To inhibit this, set the variable `find-file-run-dired' to `nil'; then it is an error to try to visit a directory. `C-x 4 f' (`find-file-other-window') is like `C-x C-f' except that the buffer containing the specified file is selected in another window. The window that was selected before `C-x 4 f' continues to show the same buffer it was already showing. If you use this command when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. *Note Windows::. `C-x 5 C-f' (`find-file-other-frame') is like `C-x C-f' except that it creates a new frame in which the file is displayed. Use the function `find-this-file-other-window' to edit a file mentioned in the buffer you are editing or to test if that file exists. To do this, use the minibuffer completion after snatching the part or all of the filename. By providing a prefix argument, the function calls `filename-at-point' and switches you to a buffer visiting the file FILENAME in another window. The function creates a buffer if none already exists. This function is similar to `find-file-other-window'. There are two hook variables that allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in the list `find-file-not-found-hooks'; the value of this variable is expected to be a list of functions which are called one by one until one of them returns non-`nil'. Any visiting of a file, whether extant or not, expects `find-file-hooks' to contain list of functions and calls them all, one by one. In both cases the functions receive no arguments. Visiting a nonexistent file runs the `find-file-not-found-hooks' first. File: xemacs.info, Node: Saving, Next: Reverting, Prev: Visiting, Up: Files Saving Files ============ "Saving" a buffer in Emacs means writing its contents back into the file that was visited in the buffer. `C-x C-s' Save the current buffer in its visited file (`save-buffer'). `C-x s' Save any or all buffers in their visited files (`save-some-buffers'). `M-~' Forget that the current buffer has been changed (`not-modified'). `C-x C-w' Save the current buffer in a specified file, and record that file as the one visited in the buffer (`write-file'). `M-x set-visited-file-name' Change file the name under which the current buffer will be saved. To save a file and make your changes permanent, type `C-x C-s' (`save-buffer'). After saving is finished, `C-x C-s' prints a message such as: Wrote /u/rms/gnu/gnu.tasks If the selected buffer is not modified (no changes have been made in it since the buffer was created or last saved), Emacs does not save it because it would have no effect. Instead, `C-x C-s' prints a message in the echo area saying: (No changes need to be saved) The command `C-x s' (`save-some-buffers') can save any or all modified buffers. First it asks, for each modified buffer, whether to save it. The questions should be answered with `y' or `n'. `C-x C-c', the key that kills Emacs, invokes `save-some-buffers' and therefore asks the same questions. If you have changed a buffer and do not want the changes to be saved, you should take some action to prevent it. Otherwise, you are liable to save it by mistake each time you use `save-some-buffers' or a related command. One thing you can do is type `M-~' (`not-modified'), which removes the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. (`~' is often used as a mathematical symbol for `not'; thus `Meta-~' is `not', metafied.) You could also use `set-visited-file-name' (see below) to mark the buffer as visiting a different file name, not in use for anything important. You can also undo all the changes made since the file was visited or saved, by reading the text from the file again. This is called "reverting". *Note Reverting::. Alternatively, you can undo all the changes by repeating the undo command `C-x u'; but this only works if you have not made more changes than the undo mechanism can remember. `M-x set-visited-file-name' alters the name of the file that the current buffer is visiting. It prompts you for the new file name in the minibuffer. You can also use `set-visited-file-name' on a buffer that is not visiting a file. The buffer's name is changed to correspond to the file it is now visiting unless the new name is already used by a different buffer; in that case, the buffer name is not changed. `set-visited-file-name' does not save the buffer in the newly visited file; it just alters the records inside Emacs so that it will save the buffer in that file. It also marks the buffer as "modified" so that `C-x C-s' will save. If you wish to mark a buffer as visiting a different file and save it right away, use `C-x C-w' (`write-file'). It is precisely equivalent to `set-visited-file-name' followed by `C-x C-s'. `C-x C-s' used on a buffer that is not visiting a file has the same effect as `C-x C-w'; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory. If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention. *Note Simultaneous Editing: Interlocking. If the variable `require-final-newline' is non-`nil', Emacs puts a newline at the end of any file that doesn't already end in one, every time a file is saved or written. Use the hook variable `write-file-hooks' to implement other ways to write files, and specify things to be done before files are written. The value of this variable should be a list of Lisp functions. When a file is to be written, the functions in the list are called, one by one, with no arguments. If one of them returns a non-`nil' value, Emacs takes this to mean that the file has been written in some suitable fashion; the rest of the functions are not called, and normal writing is not done. Use the hook variable `after-save-hook' to list all the functions to be called after writing out a buffer to a file. * Menu: * Backup:: How Emacs saves the old version of your file. * Interlocking:: How Emacs protects against simultaneous editing of one file by two users. File: xemacs.info, Node: Backup, Next: Interlocking, Prev: Saving, Up: Saving Backup Files ------------ Because Unix does not provide version numbers in file names, rewriting a file in Unix automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file--or it would, except that Emacs carefully copies the old contents to another file, called the "backup" file, before actually saving. (Make sure that the variable `make-backup-files' is non-`nil'. Backup files are not written if this variable is `nil'). At your option, Emacs can keep either a single backup file or a series of numbered backup files for each file you edit. Emacs makes a backup for a file only the first time a file is saved from one buffer. No matter how many times you save a file, its backup file continues to contain the contents from before the file was visited. Normally this means that the backup file contains the contents from before the current editing session; however, if you kill the buffer and then visit the file again, a new backup file is made by the next save. * Menu: * Names: Backup Names. How backup files are named; Choosing single or numbered backup files. * Deletion: Backup Deletion. Emacs deletes excess numbered backups. * Copying: Backup Copying. Backups can be made by copying or renaming. File: xemacs.info, Node: Backup Names, Next: Backup Deletion, Prev: Backup, Up: Backup Single or Numbered Backups .......................... If you choose to have a single backup file (the default), the backup file's name is constructed by appending `~' to the file name being edited; thus, the backup file for `eval.c' is `eval.c~'. If you choose to have a series of numbered backup files, backup file names are made by appending `.~', the number, and another `~' to the original file name. Thus, the backup files of `eval.c' would be called `eval.c.~1~', `eval.c.~2~', and so on, through names like `eval.c.~259~' and beyond. If protection stops you from writing backup files under the usual names, the backup file is written as `%backup%~' in your home directory. Only one such file can exist, so only the most recently made backup is available. The choice of single backup or numbered backups is controlled by the variable `version-control'. Its possible values are: `t' Make numbered backups. `nil' Make numbered backups for files that have numbered backups already. Otherwise, make single backups. `never' Never make numbered backups; always make single backups. `version-control' may be set locally in an individual buffer to control the making of backups for that buffer's file. For example, Rmail mode locally sets `version-control' to `never' to make sure that there is only one backup for an Rmail file. *Note Locals::. File: xemacs.info, Node: Backup Deletion, Next: Backup Copying, Prev: Backup Names, Up: Backup Automatic Deletion of Backups ............................. To prevent unlimited consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made. The two variables that control the deletion are `kept-old-versions' and `kept-new-versions'. Their values are, respectively the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The values are used just after a new backup version is made; that newly made backup is included in the count in `kept-new-versions'. By default, both variables are 2. If `trim-versions-without-asking' is non-`nil', excess middle versions are deleted without notification. If it is `nil', the default, you are asked whether the excess middle versions should really be deleted. You can also use Dired's `.' (Period) command to delete old versions. *Note Dired::. File: xemacs.info, Node: Backup Copying, Prev: Backup Deletion, Up: Backup Copying vs. Renaming .................... You can make backup files by copying the old file or by renaming it. This makes a difference when the old file has multiple names. If you rename the old file into the backup file, the alternate names become names for the backup file. If you copy the old file instead, the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents. How you make a backup file may also affect the file's owner and group. If you use copying, they do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group). Having the owner change is usually a good idea, because then the owner is always the person who last edited the file. Occasionally there is a file whose owner should not change. Since most files should change owners, it is a good idea to use local variable lists to set `backup-by-copying-when-mismatch' for the special cases where the owner should not change (*note File Variables::.). Three variables control the choice of renaming or copying. Normally, renaming is done. If the variable `backup-by-copying' is non-`nil', copying is used. Otherwise, if the variable `backup-by-copying-when-linked' is non-`nil', copying is done for files that have multiple names, but renaming may still be done when the file being edited has only one name. If the variable `backup-by-copying-when-mismatch' is non-`nil', copying is done if renaming would cause the file's owner or group to change. File: xemacs.info, Node: Interlocking, Prev: Backup, Up: Saving Protection Against Simultaneous Editing --------------------------------------- Simultaneous editing occurs when two users visit the same file, both make changes, and both save their changes. If no one was informed that this was happening, and you saved first, you would later find that your changes were lost. On some systems, Emacs notices immediately when the second user starts to change a file already being edited, and issues a warning. When this is not possible, or if the second user has started to change the file despite the warning, Emacs checks when the file is saved, and issues a second warning when a user is about to overwrite a file containing another user's changes. If you are the user editing the file, you can take corrective action at this point and prevent actual loss of work. When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that you have locked the file. (It does this by writing another file in a directory reserved for this purpose.) The lock is removed when you save the changes. The idea is that the file is locked whenever the buffer is modified. If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a collision, and Emacs asks you what to do. It does this by calling the Lisp function `ask-user-about-lock', which you can redefine to customize what it does. The standard definition of this function asks you a question and accepts three possible answers: `s' Steal the lock. Whoever was already changing the file loses the lock, and you get the lock. `p' Proceed. Go ahead and edit the file despite its being locked by someone else. `q' Quit. This causes an error (`file-locked') and the modification you were trying to make in the buffer does not actually take place. Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not realize that the two names are the same file and cannot prevent two users from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that do not really exist until they are saved. Some systems are not configured to allow Emacs to make locks. On these systems, Emacs cannot detect trouble in advance, but it can still detect it in time to prevent you from overwriting someone else's changes. Every time Emacs saves a buffer, it first checks the last-modification date of the existing file on disk to see that it has not changed since the file was last visited or saved. If the date does not match, it implies that changes were made in the file in some other way, and these changes are about to be lost if Emacs actually does save. To prevent this, Emacs prints a warning message and asks for confirmation before saving. Occasionally you will know why the file was changed and know that it does not matter; then you can answer `yes' and proceed. Otherwise, you should cancel the save with `C-g' and investigate the situation. The first thing you should do when notified that simultaneous editing has already taken place is to list the directory with `C-u C-x C-d' (*note Directory Listing: ListDir.). This will show the file's current author. You should attempt to contact that person and ask him not to continue editing. Often the next step is to save the contents of your Emacs buffer under a different name, and use `diff' to compare the two files. Simultaneous editing checks are also made when you visit a file that is already visited with `C-x C-f' and when you start to modify a file. This is not strictly necessary, but it is useful to find out about such a problem as early as possible, when corrective action takes less work. Another way to protect your file is to set the read, write, and executable permissions for the file. Use the function `set-default-file-modes' to set the UNIX `umask' value to the NMASK argument. The `umask' value is the default protection mode for new files. File: xemacs.info, Node: Reverting, Next: Auto Save, Prev: Saving, Up: Files Reverting a Buffer ================== If you have made extensive changes to a file and then change your mind about them, you can get rid of all changes by reading in the previous version of the file. To do this, use `M-x revert-buffer', which operates on the current buffer. Since reverting a buffer can result in very extensive changes, you must confirm it with `yes'. If the current buffer has been auto-saved more recently than it has been saved explicitly, `revert-buffer' offers to read the auto save file instead of the visited file (*note Auto Save::.). Emacs asks you about the auto-save file before the request for confirmation of the `revert-buffer' operation, and demands `y' or `n' as an answer. If you have started to type `yes' for confirmation without realizing that the auto-save question was going to be asked, the `y' will answer that question, but the `es' will not be valid confirmation. This gives you a chance to cancel the operation with `C-g' and try again with the answers you really intend. `revert-buffer' keeps point at the same distance (measured in characters) from the beginning of the file. If the file was edited only slightly, you will be at approximately the same piece of text after reverting as before. If you have made more extensive changes, the value of point in the old file may bring you to a totally different piece of text than your last editing point. A buffer reverted from its visited file is marked "not modified" until you make a change. Some kinds of buffers whose contents reflect data bases other than files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents from the appropriate data. Buffers created randomly with `C-x b' cannot be reverted; `revert-buffer' reports an error when asked to do so. File: xemacs.info, Node: Auto Save, Next: Version Control, Prev: Reverting, Up: Files Auto-Saving: Protection Against Disasters ========================================= Emacs saves all the visited files from time to time (based on counting your keystrokes) without being asked. This is called "auto-saving". It prevents you from losing more than a limited amount of work if the system crashes. When Emacs determines it is time for auto-saving, each buffer is considered and is auto-saved if auto-saving is turned on for it and it has changed since the last time it was auto-saved. If any auto-saving is done, the message `Auto-saving...' is displayed in the echo area until auto-saving is finished. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing. * Menu: * Files: Auto Save Files. * Control: Auto Save Control. * Recover:: Recovering text from auto-save files. File: xemacs.info, Node: Auto Save Files, Next: Auto Save Control, Prev: Auto Save, Up: Auto Save Auto-Save Files --------------- Auto-saving does not normally write to the files you visited, because it can be undesirable to save a program that is in an inconsistent state when you have made only half of a planned change. Instead, auto-saving is done in a different file called the "auto-save file", and the visited file is changed only when you save explicitly, for example, with `C-x C-s'. Normally, the name of the auto-save file is generated by appending `#' to the front and back of the visited file name. Thus, a buffer visiting file `foo.c' would be auto-saved in a file `#foo.c#'. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is generated by appending `#%' to the front and `#' to the back of buffer name. For example, the `*mail*' buffer in which you compose messages to be sent is auto-saved in a file named `#%*mail*#'. Names of auto-save files are generated this way unless you customize the functions `make-auto-save-file-name' and `auto-save-file-name-p' to do something different. The file name to be used for auto-saving a buffer is calculated at the time auto-saving is turned on in that buffer. If you want auto-saving to be done in the visited file, set the variable `auto-save-visited-file-name' to be non-`nil'. In this mode, there is really no difference between auto-saving and explicit saving. Emacs deletes a buffer's auto-save file when you explicitly save the buffer. To inhibit the deletion, set the variable `delete-auto-save-files' to `nil'. Changing the visited file name with `C-x C-w' or `set-visited-file-name' renames any auto-save file to correspond to the new visited name. File: xemacs.info, Node: Auto Save Control, Next: Recover, Prev: Auto Save Files, Up: Auto Save Controlling Auto-Saving ----------------------- Each time you visit a file, auto-saving is turned on for that file's buffer if the variable `auto-save-default' is non-`nil' (but not in batch mode; *note Entering Emacs::.). The default for this variable is `t', so Emacs auto-saves buffers that visit files by default. You can use the command `M-x auto-save-mode' to turn auto-saving for a buffer on or off. Like other minor mode commands, `M-x auto-save-mode' turns auto-saving on with a positive argument, off with a zero or negative argument; with no argument, it toggles. Emacs performs auto-saving periodically based on counting how many characters you have typed since the last time auto-saving happened. The variable `auto-save-interval' specifies the number of characters between auto-saves. By default, it is 300. Emacs also auto-saves whenever you call the function `do-auto-save'. Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as `kill -emacs', or disconnecting a phone line or network connection. You can set the number of seconds of idle time before an auto-save is done. Setting the value of the variable `auto-save-timeout' to zero or `nil' will disable auto-saving due to idleness. The actual amount of idle time between auto-saves is logarithmically related to the size of the current buffer. This variable is the number of seconds after which an auto-save will happen when the current buffer is 50k or less; the timeout will be 2 1/4 times this in a 200k buffer, 3 3/4 times this in a 1000k buffer, and 4 1/2 times this in a 2000k buffer. For this variable to have any effect, you must do `(require 'timer)'.