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Info file emacs, produced by texinfo-format-buffer -*-Text-*- from file emacs.tex This file documents the GNU Emacs editor. Copyright (C) 1985, 1986 Richard M. Stallman. 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 Emacs 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 Emacs General Public License" may be included in a translation approved by the author instead of in the original English. File: emacs Node: Regexps, Prev: Regexp Search, Up: Search, Next: Search Case Syntax of Regular Expressions ============================= Regular expressions have a syntax in which a few characters are special constructs and the rest are "ordinary". An ordinary character is a simple regular expression which matches that character and nothing else. The special characters are `$', `^', `.', `*', `+', `?', `[', `]' and `\'; no new special characters will be defined. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it. For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does not match the string `ff'.) Likewise, `o' is a regular expression that matches only `o'. Any two regular expressions A and B can be concatenated. The result is a regular expression which matches a string if A matches some amount of the beginning of that string and B matches the rest of the string. As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something nontrivial, you need to use one of the special characters. Here is a list of them. `. (Period)' is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like `a.b' which matches any three-character string which begins with `a' and ends with `b'. `*' is not a construct by itself; it is a suffix, which means the preceding regular expression is to be repeated as many times as possible. In `fo*', the `*' applies to the `o', so `fo*' matches one `f' followed by any number of `o's. The case of zero `o's is allowed: `fo*' does match `f'. `*' always applies to the smallest possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in case that makes it possible to match the rest of the pattern. For example, matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully. `+' Is a suffix character similar to `*' except that it requires that the preceding expression be matched at least once. So, for example, `ca+r' will match the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' would match all three strings. `?' Is a suffix character similar to `*' except that it can match the preceding expression either once or not at all. For example, `ca?r' will match `car' or `cr'; nothing else. `[ ... ]' `[' begins a "character set", which is terminated by a `]'. In the simplest case, the characters between the two form the set. Thus, `[ad]' matches either one `a' or one `d', and `[ad]*' matches any string composed of just `a's and `d's (including the empty string), from which it follows that `c[ad]*r' matches `cr', `car', `cdr', `caddaar', etc. Character ranges can also be included in a character set, by writing two characters with a `-' between them. Thus, `[a-z]' matches any lower-case letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case letter or `$', `%' or period. Note that the usual special characters are not special any more inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'. To include a `]' in a character set, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `---', which is a range containing only `-'. To include `^', make it other than the first character in the set. `[^ ... ]' `[^' begins a "complement character set", which matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters except letters and digits. `^' is not special in a character set unless it is the first character. The character following the `^' is treated as if it were first (`-' and `]' are not special there). Note that a complement character set can match a newline, unless newline is mentioned as one of the characters not to match. `^' is a special character that matches the empty string, but only if at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, `^foo' matches a `foo' which occurs at the beginning of a line. `$' is similar to `^' but matches only at the end of a line. Thus, `xx*$' matches a string of one `x' or more at the end of a line. `\' has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs. Because `\' quotes special characters, `\$' is a regular expression which matches only `$', and `\[' is a regular expression which matches only `[', and so on. Note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; better to quote the special character anyway, regardless of where is appears. For the most part, `\' followed by any character matches only that character. However, there are several exceptions: characters which, when preceded by `\', are special constructs. Such characters are always ordinary when encountered on their own. Here is a table of `\' constructs. `\|' specifies an alternative. Two regular expressions A and B with `\|' in between form an expression that matches anything that either A or B will match. Thus, `foo\|bar' matches either `foo' or `bar' but no other string. `\|' applies to the largest possible surrounding expressions. Only a surrounding `$ ... $' grouping can limit the grouping power of `\|'. Full backtracking capability exists to handle multiple uses of `\|'. `$ ... $' is a grouping construct that serves three purposes: 1. To enclose a set of `\|' alternatives for other operations. Thus, `$foo\|bar$x' matches either `foox' or `barx'. 2. To enclose a complicated expression for the postfix `*' to operate on. Thus, `ba$na$*' matches `bananana', etc., with any (zero or more) number of `na' strings. 3. To mark a matched substring for future reference. This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature which happens to be assigned as a second meaning to the same `$ ... $' construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature: `\DIGIT' after the end of a `$ ... $' construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use `\' followed by DIGIT to mean "match the same text matched the DIGIT'th time by the `$ ... $' construct." The strings matching the first nine `$ ... $' constructs appearing in a regular expression are assigned numbers 1 through 9 in order that the open-parentheses appear in the regular expression. `\1' through `\9' may be used to refer to the text matched by the corresponding `$ ... $' construct. For example, `$.*$\1' matches any newline-free string that is composed of two identical halves. The `$.*$' matches the first half, which may be anything, but the `\1' that follows must match the same exact text. `\`' matches the empty string, provided it is at the beginning of the buffer. `\'' matches the empty string, provided it is at the end of the buffer. `\b' matches the empty string, provided it is at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word. `\B' matches the empty string, provided it is not at the beginning or end of a word. `\<' matches the empty string, provided it is at the beginning of a word. `\>' matches the empty string, provided it is at the end of a word. `\w' matches any word-constituent character. The editor syntax table determines which characters these are. `\W' matches any character that is not a word-constituent. `\sCODE' matches any character whose syntax is CODE. CODE is a character which represents a syntax code: thus, `w' for word constituent, `-' for whitespace, `(' for open-parenthesis, etc. *Note Syntax::. `\SCODE' matches any character whose syntax is not CODE. Here is a complicated regexp, used by Emacs to recognize the end of a sentence together with any whitespace that follows. It is given in Lisp syntax to enable you to distinguish the spaces from the tab characters. In Lisp syntax, the string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the regexp, `\\' for a backslash as part of the regexp, `\t' for a tab and `\n' for a newline. "[.?!][]\"')]*\$$\\|\t\\| \$[ \t\n]*" This contains four parts in succession: a character set matching period, `?' or `!'; a character set matching close-brackets, quotes or parentheses, repeated any number of times; an alternative in backslash-parentheses that matches end-of-line, a tab or two spaces; and a character set matching whitespace characters, repeated any number of times. File: emacs Node: Search Case, Prev: Regexps, Up: Search, Next: Replace Searching and Case ================== All sorts of searches in Emacs normally ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' and `foo' are also considered a match. Regexps, and in particular character sets, are included: `[aB]' would match `a' or `A' or `b' or `B'. If you do not want this feature, set the variable `case-fold-search' to `nil'. Then all letters must match exactly, including case. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. *Note Locals::. File: emacs Node: Replace, Prev: Search Case, Up: Search, Next: Other Repeating 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 the 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: emacs Node: Unconditional Replace, Prev: Replace, Up: Replace, Next: Regexp 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, so if you want to cover the whole buffer you must go to the beginning first. 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: emacs Node: Regexp Replace, Prev: Unconditional Replace, Up: Replace, Next: Replacement and Case 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: emacs Node: Replacement and Case, Prev: Regexp Replace, Up: Replace, Next: Query Replace Replace Commands and Case ------------------------- If the arguments to a replace command are in lower case, it preserves case when it makes a replacement. Thus, the 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: emacs 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, then you cannot use an ordinary `replace-string'. Instead, use `M-%' (`query-replace'). 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 asked for another input character, except that since the replacement has already been made, DEL and SPC are equivalent. You could type `C-r' at this point (see below) to alter the replaced text. You could also type `C-x u' to undo the replacement; this exits the `query-replace', so 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, the `query-replace' is exited, and the character executed 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: emacs 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 the 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: emacs Node: Fixit, Prev: Search, Up: Top, Next: Files Commands for Fixing Typos ************************* In this chapter we describe the commands that are especially useful for the times when you catch a mistake in your text just after you have made it, or 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: emacs Node: Kill Errors, Prev: Fixit, Up: Fixit, Next: Transpose 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 again. File: emacs Node: Transpose, Prev: Kill Errors, Up: Fixit, Next: Fixing Case 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 characters can be fixed, when they are adjacent, 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, rather than transposing the last character of the line with the newline, which would be useless, `C-t' transposes the last two characters on the line. So, if you catch your transposition error right away, you can fix it with just a `C-t'. If you don't catch it so fast, you must 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. They work like `M-t' except in determining the division of the text into syntactic units. 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 is assigned a special meaning (because otherwise a command with a repeat count of zero would do nothing): to transpose the character (word, sexp, line) ending after point with the one ending after the mark. File: emacs Node: Fixing Case, Prev: Transpose, Up: Fixit, Next: Spelling Case Conversion =============== `M-- M-l' Convert last word to lower case. Note `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 very 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' have a special feature when used with a negative argument: they do not move the cursor. As soon as you see you have mistyped the last word, you can simply case-convert it and go on typing. *Note Case::. File: emacs Node: Spelling, Prev: Fixing Case, Up: Fixit Checking and Correcting Spelling ================================ `M-$' Check and correct spelling of word (`spell-word'). `M-x spell-buffer' Check and correct spelling of each word in the buffer. `M-x spell-region' Check and correct spelling of each word in the region. `M-x spell-string' Check spelling of specified word. To check the spelling of the word before point, and optionally correct it as well, use the command `M-$' (`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 does 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. Then 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' if appropriate for every incorrect word. `M-x spell-region' is similar 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 in the echo area a message giving the answer. File: emacs Node: Files, Prev: Fixit, Up: Top, Next: Buffers 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. * ListDir:: Listing the contents of a file directory. * Dired:: "Editing" a directory to delete, rename, etc. the files in it. * Misc File Ops:: Other things you can do on files. File: emacs Node: File Names, Prev: Files, Up: Files, Next: Visiting 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 using 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 will be used if you type just RET, entering an empty argument. 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, if you do not specify a directory, the default directory is used. 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 is kept in the variable `default-directory', which has a separate value in every buffer. 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 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 made randomly with `C-x b', its default directory is copied from that of the buffer that was current at the time. The default directory 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. This insertion of the default directory is inhibited if the variable `insert-default-directory' is set 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 as part of the text. 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 `$' at the same time as variable substitution is performed for single `$'. 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: emacs Node: Visiting, Prev: File Names, Up: Files, Next: Saving 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. "Visiting" a file means copying its contents into Emacs where you can edit them. Emacs makes a new buffer for each file that 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, keeping just the name proper. For example, a file named `/usr/rms/emacs.tex' would get a buffer named `emacs.tex'. If there is already a buffer with that name, a unique name is constructed by appending `<2>', `<3>', or 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 visited, or any place permanent, 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. 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'. Your confirmation that `C-x C-f' has completed successfully is the appearance of new text on the screen and a new buffer name in the mode line. If the specified file does not exist and could not be created, or cannot be read, then an error results. The error message is printed in the echo area, and includes the file name which 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, a warning message is printed. *Note Simultaneous Editing: Interlocking. What 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::). This can be inhibited by setting 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 this command is used when only one window is being displayed, that window is split in two, with one window showing the same before as before, and the other one showing the newly requested file. *Note Windows::. 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, and the functions 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: emacs Node: Saving, Prev: Visiting, Up: Files, Next: Reverting 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. When you wish to save the 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), saving is not really done, because it would have no effect. Instead, `C-x C-s' prints a message in the echo area saying (No changes need to be written) 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. These 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, each time you use `save-some-buffers' you are liable to save it by mistake. One thing you can do is type `M-~' (`not-modified'), which clears out 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, one which is not in use for anything important. Alternatively, you can 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::. You could also undo all the changes by repeating the undo command `C-x u' until you have undone all the changes; 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 reads the new file name using the minibuffer. It can be used on a buffer that is not visiting a file, too. The buffer's name is changed to correspond to the file it is now visiting in the usual fashion (unless the new name is in use already for some other 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, if you save the buffer, it will be saved in that file. It also marks the buffer as "modified" so that `C-x C-s' will save. If you wish to mark the 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 with 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. You can implement other ways to write files, and other things to be done before writing them, using the hook variable `write-file-hooks'. 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. * 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: emacs Node: Backup, Prev: Saving, Up: Saving, Next: Interlocking 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. (Provided 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 that you edit. Emacs makes a backup for a file only the first time the 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 will be 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: emacs Node: Backup Names, Prev: Backup, Up: Backup, Next: Backup Deletion Single or Numbered Backups .......................... If you choose to have a single backup file (this is the default), the backup file's name is constructed by appending `~' to the file name being edited; thus, the backup file for `eval.c' would be `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 such 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' Do not in any case 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: emacs Node: Backup Deletion, Prev: Backup Names, Up: Backup, Next: Backup Copying 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. Recall that these 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', the excess middle versions are deleted without a murmur. If it is `nil', the default, then you are asked whether the excess middle versions should really be deleted. Dired's `.' (Period) command can also be used to delete old versions. *Note Dired::. File: emacs Node: Backup Copying, Prev: Backup Deletion, Up: Backup Copying vs. Renaming .................... Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names. If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents. The method of making a backup file may also affect the file's owner and group. If copying is used, these 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 always shows who last edited the file. Also, the owners of the backups show who produced those versions. Occasionally there is a file whose owner should not change; it is a good idea for such files to contain local variable lists to set `backup-by-copying-when-mismatch' for them alone (*Note File Variables::). The choice of renaming or copying is controlled by three variables. 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', then copying is done for files that have multiple names, but renaming may still done when the file being edited has only one name. If the variable `backup-by-copying-when-mismatch' is non-`nil', then copying is done if renaming would cause the file's owner or group to change. File: emacs Node: Interlocking, Prev: Backup, Up: Saving Protection against Simultaneous Editing --------------------------------------- Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody were informed that this was happening, whichever user saved first would later find that his changes were lost. On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. When this is not possible, or if the second user has gone on to change the file despite the warning, Emacs checks later 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 the editing user takes the proper corrective action at this point, he can 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 for the sake of customization. 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 gain 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 user from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that will 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 still can 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 him to warn 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 with `C-x C-f' a file that is already visited and when you start to modify a file. This is not strictly necessary, but it can cause you to find out about the problem earlier, when perhaps correction takes less work.