@c This is part of the Emacs manual. @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc. @c See file emacs.texi for copying conditions. @node Search, Fixit, Display, Top @chapter Searching and Replacement @cindex searching @cindex finding strings within text Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is @dfn{incremental}; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors. Besides the usual @code{replace-string} command that finds all occurrences of one string and replaces them with another, Emacs has a fancy replacement command called @code{query-replace} which asks interactively which occurrences to replace. @menu * Incremental Search:: Search happens as you type the string. * Nonincremental Search:: Specify entire string and then search. * Word Search:: Search for sequence of words. * Regexp Search:: Search for match for a regexp. * Regexps:: Syntax of regular expressions. * Search Case:: To ignore case while searching, or not. * Replace:: Search, and replace some or all matches. * Other Repeating Search:: Operating on all matches for some regexp. @end menu @node Incremental Search, Nonincremental Search, Search, Search @section Incremental Search @cindex incremental search An incremental search begins searching as soon as you type the first character of the search string. As you type in the search string, Emacs shows you where the string (as you have typed it so far) would be found. When you have typed enough characters to identify the place you want, you can stop. Depending on what you plan to do next, you may or may not need to terminate the search explicitly with @key{RET}. @c WideCommands @table @kbd @item C-s Incremental search forward (@code{isearch-forward}). @item C-r Incremental search backward (@code{isearch-backward}). @end table @kindex C-s @findex isearch-forward @kbd{C-s} starts an incremental search. @kbd{C-s} reads characters from the keyboard and positions the cursor at the first occurrence of the characters that you have typed. If you type @kbd{C-s} and then @kbd{F}, the cursor moves right after the first @samp{F}. Type an @kbd{O}, and see the cursor move to after the first @samp{FO}. After another @kbd{O}, the cursor is after the first @samp{FOO} after the place where you started the search. At each step, the buffer text that matches the search string is highlighted, if the terminal can do that; at each step, the current search string is updated in the echo area. If you make a mistake in typing the search string, you can cancel characters with @key{DEL}. Each @key{DEL} cancels the last character of search string. This does not happen until Emacs is ready to read another input character; first it must either find, or fail to find, the character you want to erase. If you do not want to wait for this to happen, use @kbd{C-g} as described below. When you are satisfied with the place you have reached, you can type @key{RET}, which stops searching, leaving the cursor where the search brought it. Also, any command not specially meaningful in searches stops the searching and is then executed. Thus, typing @kbd{C-a} would exit the search and then move to the beginning of the line. @key{RET} is necessary only if the next command you want to type is a printing character, @key{DEL}, @key{RET}, or another control character that is special within searches (@kbd{C-q}, @kbd{C-w}, @kbd{C-r}, @kbd{C-s}, @kbd{C-y}, @kbd{M-y}, @kbd{M-r}, or @kbd{M-s}). Sometimes you search for @samp{FOO} and find it, but not the one you expected to find. There was a second @samp{FOO} that you forgot about, before the one you were aiming for. In this event, type another @kbd{C-s} to move to the next occurrence of the search string. This can be done any number of times. If you overshoot, you can cancel some @kbd{C-s} characters with @key{DEL}. After you exit a search, you can search for the same string again by typing just @kbd{C-s C-s}: the first @kbd{C-s} is the key that invokes incremental search, and the second @kbd{C-s} means ``search again.'' To reuse earlier search strings, use the @dfn{search ring}. The commands @kbd{M-p} and @kbd{M-n} move through the ring to pick a search string to reuse. These commands leave the selected search ring element in the minibuffer, where you can edit it. Type @kbd{C-s} or @kbd{C-r} to terminate editing the string and search for it. If your string is not found at all, the echo area says @samp{Failing I-Search}. The cursor is after the place where Emacs found as much of your string as it could. Thus, if you search for @samp{FOOT}, and there is no @samp{FOOT}, you might see the cursor after the @samp{FOO} in @samp{FOOL}. At this point there are several things you can do. If your string was mistyped, you can rub some of it out and correct it. If you like the place you have found, you can type @key{RET} or some other Emacs command to ``accept what the search offered.'' Or you can type @kbd{C-g}, which removes from the search string the characters that could not be found (the @samp{T} in @samp{FOOT}), leaving those that were found (the @samp{FOO} in @samp{FOOT}). A second @kbd{C-g} at that point cancels the search entirely, returning point to where it was when the search started. An upper-case letter in the search string makes the search case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. @xref{Search Case}. If a search is failing and you ask to repeat it by typing another @kbd{C-s}, it starts again from the beginning of the buffer. Repeating a failing reverse search with @kbd{C-r} starts again from the end. This is called @dfn{wrapping around}. @samp{Wrapped} appears in the search prompt once this has happened. If you keep on going past the original starting point of the search, it changes to @samp{Overwrapped}, which means that you are revisiting matches that you have already seen. @cindex quitting (in search) The @kbd{C-g} ``quit'' character does special things during searches; just what it does depends on the status of the search. If the search has found what you specified and is waiting for input, @kbd{C-g} cancels the entire search. The cursor moves back to where you started the search. If @kbd{C-g} is typed when there are characters in the search string that have not been found---because Emacs is still searching for them, or because it has failed to find them---then the search string characters which have not been found are discarded from the search string. With them gone, the search is now successful and waiting for more input, so a second @kbd{C-g} will cancel the entire search. To search for a newline, type @kbd{C-j}. To search for another control character, such as control-S or carriage return, you must quote it by typing @kbd{C-q} first. This function of @kbd{C-q} is analogous to its use for insertion (@pxref{Inserting Text}): it causes the following character to be treated the way any ``ordinary'' character is treated in the same context. You can also specify a character by its octal code: enter @kbd{C-q} followed by a sequence of octal digits. You can change to searching backwards with @kbd{C-r}. If a search fails because the place you started was too late in the file, you should do this. Repeated @kbd{C-r} keeps looking for more occurrences backwards. A @kbd{C-s} starts going forwards again. @kbd{C-r} in a search can be canceled with @key{DEL}. @kindex C-r @findex isearch-backward If you know initially that you want to search backwards, you can use @kbd{C-r} instead of @kbd{C-s} to start the search, because @kbd{C-r} as a key runs a command (@code{isearch-backward}) to search backward. A backward search finds matches that are entirely before the starting point, just as a forward search finds matches that begin after it. The characters @kbd{C-y} and @kbd{C-w} can be used in incremental search to grab text from the buffer into the search string. This makes it convenient to search for another occurrence of text at point. @kbd{C-w} copies the word after point as part of the search string, advancing point over that word. Another @kbd{C-s} to repeat the search will then search for a string including that word. @kbd{C-y} is similar to @kbd{C-w} but copies all the rest of the current line into the search string. Both @kbd{C-y} and @kbd{C-w} convert the text they copy to lower case if the search is currently not case-sensitive; this is so the search remains case-insensitive. The character @kbd{M-y} copies text from the kill ring into the search string. It uses the same text that @kbd{C-y} as a command would yank. @xref{Yanking}. When you exit the incremental search, it sets the mark to where point @emph{was}, before the search. That is convenient for moving back there. In Transient Mark mode, incremental search sets the mark without activating it, and does so only if the mark is not already active. @vindex isearch-mode-map To customize the special characters that incremental search understands, alter their bindings in the keymap @code{isearch-mode-map}. For a list of bindings, look at the documentation of @code{isearch-mode} with @kbd{C-h f isearch-mode @key{RET}}. @subsection Slow Terminal Incremental Search Incremental search on a slow terminal uses a modified style of display that is designed to take less time. Instead of redisplaying the buffer at each place the search gets to, it creates a new single-line window and uses that to display the line that the search has found. The single-line window comes into play as soon as point gets outside of the text that is already on the screen. When you terminate the search, the single-line window is removed. Then Emacs redisplays the window in which the search was done, to show its new position of point. @ignore The three dots at the end of the search string, normally used to indicate that searching is going on, are not displayed in slow style display. @end ignore @vindex search-slow-speed The slow terminal style of display is used when the terminal baud rate is less than or equal to the value of the variable @code{search-slow-speed}, initially 1200. @vindex search-slow-window-lines The number of lines to use in slow terminal search display is controlled by the variable @code{search-slow-window-lines}. Its normal value is 1. @node Nonincremental Search, Word Search, Incremental Search, Search @section Nonincremental Search @cindex nonincremental search Emacs also has conventional nonincremental search commands, which require you to type the entire search string before searching begins. @table @kbd @item C-s @key{RET} @var{string} @key{RET} Search for @var{string}. @item C-r @key{RET} @var{string} @key{RET} Search backward for @var{string}. @end table To do a nonincremental search, first type @kbd{C-s @key{RET}}. This enters the minibuffer to read the search string; terminate the string with @key{RET}, and then the search takes place. If the string is not found, the search command gets an error. The way @kbd{C-s @key{RET}} works is that the @kbd{C-s} invokes incremental search, which is specially programmed to invoke nonincremental search if the argument you give it is empty. (Such an empty argument would otherwise be useless.) @kbd{C-r @key{RET}} also works this way. However, nonincremental searches performed using @kbd{C-s @key{RET}} do not call @code{search-forward} right away. The first thing done is to see if the next character is @kbd{C-w}, which requests a word search. @ifinfo @xref{Word Search}. @end ifinfo @findex search-forward @findex search-backward Forward and backward nonincremental searches are implemented by the commands @code{search-forward} and @code{search-backward}. These commands may be bound to keys in the usual manner. The feature that you can get to them via the incremental search commands exists for historical reasons, and to avoid the need to find suitable key sequences for them. @node Word Search, Regexp Search, Nonincremental Search, Search @section Word Search @cindex word search Word search searches for a sequence of words without regard to how the words are separated. More precisely, you type a string of many words, using single spaces to separate them, and the string can be found even if there are multiple spaces, newlines or other punctuation between the words. Word search is useful for editing a printed document made with a text formatter. If you edit while looking at the printed, formatted version, you can't tell where the line breaks are in the source file. With word search, you can search without having to know them. @table @kbd @item C-s @key{RET} C-w @var{words} @key{RET} Search for @var{words}, ignoring details of punctuation. @item C-r @key{RET} C-w @var{words} @key{RET} Search backward for @var{words}, ignoring details of punctuation. @end table Word search is a special case of nonincremental search and is invoked with @kbd{C-s @key{RET} C-w}. This is followed by the search string, which must always be terminated with @key{RET}. Being nonincremental, this search does not start until the argument is terminated. It works by constructing a regular expression and searching for that; see @ref{Regexp Search}. Use @kbd{C-r @key{RET} C-w} to do backward word search. @findex word-search-forward @findex word-search-backward Forward and backward word searches are implemented by the commands @code{word-search-forward} and @code{word-search-backward}. These commands may be bound to keys in the usual manner. The feature that you can get to them via the incremental search commands exists for historical reasons, and to avoid the need to find suitable key sequences for them. @node Regexp Search, Regexps, Word Search, Search @section Regular Expression Search @cindex regular expression @cindex regexp A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that denotes a class of alternative strings to match, possibly infinitely many. In GNU Emacs, you can search for the next match for a regexp either incrementally or not. @kindex C-M-s @findex isearch-forward-regexp @kindex C-M-r @findex isearch-backward-regexp Incremental search for a regexp is done by typing @kbd{C-M-s} (@code{isearch-forward-regexp}). This command reads a search string incrementally just like @kbd{C-s}, but it treats the search string as a regexp rather than looking for an exact match against the text in the buffer. Each time you add text to the search string, you make the regexp longer, and the new regexp is searched for. Invoking @kbd{C-s} with a prefix argument (its value does not matter) is another way to do a forward incremental regexp search. To search backward for a regexp, use @kbd{C-M-r} (@code{isearch-backward-regexp}), or @kbd{C-r} with a prefix argument. All of the control characters that do special things within an ordinary incremental search have the same function in incremental regexp search. Typing @kbd{C-s} or @kbd{C-r} immediately after starting the search retrieves the last incremental search regexp used; that is to say, incremental regexp and non-regexp searches have independent defaults. They also have separate search rings that you can access with @kbd{M-p} and @kbd{M-n}. If you type @key{SPC} in incremental regexp search, it matches any sequence of whitespace characters, including newlines. If you want to match just a space, type @kbd{C-q @key{SPC}}. Note that adding characters to the regexp in an incremental regexp search can make the cursor move back and start again. For example, if you have searched for @samp{foo} and you add @samp{\|bar}, the cursor backs up in case the first @samp{bar} precedes the first @samp{foo}. @findex re-search-forward @findex re-search-backward Nonincremental search for a regexp is done by the functions @code{re-search-forward} and @code{re-search-backward}. You can invoke these with @kbd{M-x}, or bind them to keys, or invoke them by way of incremental regexp search with @kbd{C-M-s @key{RET}} and @kbd{C-M-r @key{RET}}. If you use the incremental regexp search commands with a prefix argument, they perform ordinary string search, like @code{isearch-forward} and @code{isearch-backward}. @xref{Incremental Search}. @node Regexps, Search Case, Regexp Search, Search @section Syntax of Regular Expressions @cindex regexp syntax Regular expressions have a syntax in which a few characters are special constructs and the rest are @dfn{ordinary}. An ordinary character is a simple regular expression which matches that same character and nothing else. The special characters are @samp{$}, @samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, @samp{]} and @samp{\}. Any other character appearing in a regular expression is ordinary, unless a @samp{\} precedes it. For example, @samp{f} is not a special character, so it is ordinary, and therefore @samp{f} is a regular expression that matches the string @samp{f} and no other string. (It does @emph{not} match the string @samp{ff}.) Likewise, @samp{o} is a regular expression that matches only @samp{o}. (When case distinctions are being ignored, these regexps also match @samp{F} and @samp{O}, but we consider this a generalization of ``the same string,'' rather than an exception.) Any two regular expressions @var{a} and @var{b} can be concatenated. The result is a regular expression which matches a string if @var{a} matches some amount of the beginning of that string and @var{b} matches the rest of the string.@refill As a simple example, we can concatenate the regular expressions @samp{f} and @samp{o} to get the regular expression @samp{fo}, which matches only the string @samp{fo}. Still trivial. To do something nontrivial, you need to use one of the special characters. Here is a list of them. @table @kbd @item .@: @r{(Period)} is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like @samp{a.b}, which matches any three-character string that begins with @samp{a} and ends with @samp{b}.@refill @item * is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, @samp{o*} matches any number of @samp{o}s (including no @samp{o}s). @samp{*} always applies to the @emph{smallest} possible preceding expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. The matcher processes a @samp{*} 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 @samp{*}-modified construct in case that makes it possible to match the rest of the pattern. For example, in matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} first tries to match all three @samp{a}s; but the rest of the pattern is @samp{ar} and there is only @samp{r} left to match, so this try fails. The next alternative is for @samp{a*} to match only two @samp{a}s. With this choice, the rest of the regexp matches successfully.@refill @item + is a postfix operator, similar to @samp{*} except that it must match the preceding expression at least once. So, for example, @samp{ca+r} matches the strings @samp{car} and @samp{caaaar} but not the string @samp{cr}, whereas @samp{ca*r} matches all three strings. @item ? is a postfix operator, similar to @samp{*} except that it can match the preceding expression either once or not at all. For example, @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. @item [ @dots{} ] is a @dfn{character set}, which begins with @samp{[} and is terminated by @samp{]}. In the simplest case, the characters between the two brackets are what this set can match. Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s (including the empty string), from which it follows that @samp{c[ad]*r} matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. You can also include character ranges in a character set, by writing the starting and ending characters with a @samp{-} between them. Thus, @samp{[a-z]} matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in @samp{[a-z$%.]}, which matches any lower-case ASCII letter or @samp{$}, @samp{%} or period. Note that the usual regexp special characters are not special inside a character set. A completely different set of special characters exists inside character sets: @samp{]}, @samp{-} and @samp{^}. To include a @samp{]} in a character set, you must make it the first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. To include a @samp{-}, write @samp{-} as the first or last character of the set, or put it after a range. Thus, @samp{[]-]} matches both @samp{]} and @samp{-}. To include @samp{^} in a set, put it anywhere but at the beginning of the set. When you use a range in case-insensitive search, you should write both ends of the range in upper case, or both in lower case, or both should be non-letters. The behavior of a mixed-case range such as @samp{A-z} is somewhat ill-defined, and it may change in future Emacs versions. @item [^ @dots{} ] @samp{[^} begins a @dfn{complemented character set}, which matches any character except the ones specified. Thus, @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and digits. @samp{^} is not special in a character set unless it is the first character. The character following the @samp{^} is treated as if it were first (in other words, @samp{-} and @samp{]} are not special there). A complemented character set can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as @code{grep}. @item ^ is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at the beginning of a line. @item $ is similar to @samp{^} but matches only at the end of a line. Thus, @samp{x+$} matches a string of one @samp{x} or more at the end of a line. @item \ has two functions: it quotes the special characters (including @samp{\}), and it introduces additional special constructs. Because @samp{\} quotes special characters, @samp{\$} is a regular expression that matches only @samp{$}, and @samp{\[} is a regular expression that matches only @samp{[}, and so on. @end table 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, @samp{*foo} treats @samp{*} as ordinary since there is no preceding expression on which the @samp{*} can act. It is poor practice to depend on this behavior; it is better to quote the special character anyway, regardless of where it appears.@refill For the most part, @samp{\} followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with @samp{\} that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of @samp{\} constructs. @table @kbd @item \| specifies an alternative. Two regular expressions @var{a} and @var{b} with @samp{\|} in between form an expression that matches some text if either @var{a} matches it or @var{b} matches it. It works by trying to match @var{a}, and if that fails, by trying to match @var{b}. Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} but no other string.@refill @samp{\|} applies to the largest possible surrounding expressions. Only a surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of @samp{\|}.@refill Full backtracking capability exists to handle multiple uses of @samp{\|}. @item \( @dots{} \) is a grouping construct that serves three purposes: @enumerate @item To enclose a set of @samp{\|} alternatives for other operations. Thus, @samp{\(foo\|bar\)x} matches either @samp{foox} or @samp{barx}. @item To enclose a complicated expression for the postfix operators @samp{*}, @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches @samp{bananana}, etc., with any (zero or more) number of @samp{na} strings.@refill @item To record a matched substring for future reference. @end enumerate This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same @samp{\( @dots{} \)} construct. In practice there is no conflict between the two meanings. @item \@var{d} matches the same text that matched the @var{d}th occurrence of a @samp{\( @dots{} \)} construct. After the end of a @samp{\( @dots{} \)} 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 @samp{\} followed by the digit @var{d} to mean ``match the same text matched the @var{d}th time by the @samp{\( @dots{} \)} construct.'' The strings matching the first nine @samp{\( @dots{} \)} constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open-parentheses appear in the regular expression. So you can use @samp{\1} through @samp{\9} to refer to the text matched by the corresponding @samp{\( @dots{} \)} constructs. For example, @samp{\(.*\)\1} matches any newline-free string that is composed of two identical halves. The @samp{\(.*\)} matches the first half, which may be anything, but the @samp{\1} that follows must match the same exact text. If a particular @samp{\( @dots{} \)} construct matches more than once (which can easily happen if it is followed by @samp{*}), only the last match is recorded. @item \` matches the empty string, but only at the beginning of the buffer or string being matched against. @item \' matches the empty string, but only at the end of the buffer or string being matched against. @item \= matches the empty string, but only at point. @item \b matches the empty string, but only at the beginning or end of a word. Thus, @samp{\bfoo\b} matches any occurrence of @samp{foo} as a separate word. @samp{\bballs?\b} matches @samp{ball} or @samp{balls} as a separate word.@refill @samp{\b} matches at the beginning or end of the buffer regardless of what text appears next to it. @item \B matches the empty string, but @emph{not} at the beginning or end of a word. @item \< matches the empty string, but only at the beginning of a word. @samp{\<} matches at the beginning of the buffer only if a word-constituent character follows. @item \> matches the empty string, but only at the end of a word. @samp{\>} matches at the end of the buffer only if the contents end with a word-constituent character. @item \w matches any word-constituent character. The syntax table determines which characters these are. @xref{Syntax}. @item \W matches any character that is not a word-constituent. @item \s@var{c} matches any character whose syntax is @var{c}. Here @var{c} is a character that represents a syntax code: thus, @samp{w} for word constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, etc. Represent a character of whitespace (which can be a newline) by either @samp{-} or a space character. @item \S@var{c} matches any character whose syntax is not @var{c}. @end table The constructs that pertain to words and syntax are controlled by the setting of the syntax table (@pxref{Syntax}). 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. @samp{\"} stands for a double-quote as part of the regexp, @samp{\\} for a backslash as part of the regexp, @samp{\t} for a tab and @samp{\n} for a newline. @example "[.?!][]\"')]*\\($\\|\t\\| \\)[ \t\n]*" @end example @noindent This contains four parts in succession: a character set matching period, @samp{?}, or @samp{!}; 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. To enter the same regexp interactively, you would type @key{TAB} to enter a tab, and @kbd{C-j} to enter a newline. You would also type single backslashes as themselves, instead of doubling them for Lisp syntax. @node Search Case, Replace, Regexps, Search @section Searching and Case @vindex case-fold-search Incremental searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for @samp{foo}, then @samp{Foo} and @samp{foo} are also considered a match. Regexps, and in particular character sets, are included: @samp{[ab]} would match @samp{a} or @samp{A} or @samp{b} or @samp{B}.@refill An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for @samp{Foo} does not find @samp{foo} or @samp{FOO}. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string. If you set the variable @code{case-fold-search} to @code{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. @xref{Locals}. This variable applies to nonincremental searches also, including those performed by the replace commands (@pxref{Replace}) and the minibuffer history matching commands (@pxref{Minibuffer History}). @node Replace, Other Repeating Search, Search Case, Search @section Replacement Commands @cindex replacement @cindex search-and-replace commands @cindex string substitution @cindex global substitution Global search-and-replace operations are not needed as often in Emacs as they are in other editors@footnote{In some editors, search-and-replace operations are the only convenient way to make a single change in the text.}, but they are available. In addition to the simple @kbd{M-x replace-string} command which is like that found in most editors, there is a @kbd{M-x query-replace} command which asks you, for each occurrence of the pattern, whether to replace it. The replace commands normally operate on the text from point to the end of the buffer; however, in Transient Mark mode, when the mark is active, they operate on the region. 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 @code{expand-region-abbrevs} (@pxref{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. @end menu @node Unconditional Replace, Regexp Replace, Replace, Replace @subsection Unconditional Replacement @findex replace-string @findex replace-regexp @table @kbd @item M-x replace-string @key{RET} @var{string} @key{RET} @var{newstring} @key{RET} Replace every occurrence of @var{string} with @var{newstring}. @item M-x replace-regexp @key{RET} @var{regexp} @key{RET} @var{newstring} @key{RET} Replace every match for @var{regexp} with @var{newstring}. @end table To replace every instance of @samp{foo} after point with @samp{bar}, use the command @kbd{M-x replace-string} with the two arguments @samp{foo} and @samp{bar}. Replacement happens only in the text 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 (@pxref{Narrowing}). In Transient Mark mode, when the region is active, replacement is limited to the region (@pxref{Transient Mark}). When @code{replace-string} exits, it leaves point at the last occurrence replaced. It sets the mark to the prior position of point (where the @code{replace-string} command was issued); use @kbd{C-u C-@key{SPC}} to move back there. A numeric argument restricts replacement to matches that are surrounded by word boundaries. The argument's value doesn't matter. @node Regexp Replace, Replacement and Case, Unconditional Replace, Replace @subsection Regexp Replacement The @kbd{M-x replace-string} command replaces exact matches for a single string. The similar command @kbd{M-x replace-regexp} replaces any match for a specified pattern. In @code{replace-regexp}, the @var{newstring} need not be constant: it can refer to all or part of what is matched by the @var{regexp}. @samp{\&} in @var{newstring} stands for the entire match being replaced. @samp{\@var{d}} in @var{newstring}, where @var{d} is a digit, stands for whatever matched the @var{d}th parenthesized grouping in @var{regexp}. To include a @samp{\} in the text to replace with, you must enter @samp{\\}. For example, @example M-x replace-regexp @key{RET} c[ad]+r @key{RET} \&-safe @key{RET} @end example @noindent replaces (for example) @samp{cadr} with @samp{cadr-safe} and @samp{cddr} with @samp{cddr-safe}. @example M-x replace-regexp @key{RET} \(c[ad]+r\)-safe @key{RET} \1 @key{RET} @end example @noindent performs the inverse transformation. @node Replacement and Case, Query Replace, Regexp Replace, Replace @subsection Replace Commands and Case If the first argument of a replace command is all lower case, the commands ignores case while searching for occurrences to replace---provided @code{case-fold-search} is non-@code{nil}. If @code{case-fold-search} is set to @code{nil}, case is always significant in all searches. @vindex case-replace In addition, when the @var{newstring} argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command @example M-x replace-string @key{RET} foo @key{RET} bar @key{RET} @end example @noindent replaces a lower case @samp{foo} with a lower case @samp{bar}, an all-caps @samp{FOO} with @samp{BAR}, and a capitalized @samp{Foo} with @samp{Bar}. (These three alternatives---lower case, all caps, and capitalized, are the only ones that @code{replace-string} can distinguish.) If upper-case letters are used in the replacement string, they remain upper case every time that text 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 either @code{case-replace} or @code{case-fold-search} is set to @code{nil}, replacement is done without case conversion. @node Query Replace,, Replacement and Case, Replace @subsection Query Replace @cindex query replace @table @kbd @item M-% @var{string} @key{RET} @var{newstring} @key{RET} @itemx M-x query-replace @key{RET} @var{string} @key{RET} @var{newstring} @key{RET} Replace some occurrences of @var{string} with @var{newstring}. @item C-M-% @var{regexp} @key{RET} @var{newstring} @key{RET} @itemx M-x query-replace-regexp @key{RET} @var{regexp} @key{RET} @var{newstring} @key{RET} Replace some matches for @var{regexp} with @var{newstring}. @end table @kindex M-% @findex query-replace If you want to change only some of the occurrences of @samp{foo} to @samp{bar}, not all of them, then you cannot use an ordinary @code{replace-string}. Instead, use @kbd{M-%} (@code{query-replace}). This command finds occurrences of @samp{foo} one by one, displays each occurrence and asks you whether to replace it. A numeric argument to @code{query-replace} tells it to consider only occurrences that are bounded by word-delimiter characters. This preserves case, just like @code{replace-string}, provided @code{case-replace} is non-@code{nil}, as it normally is. @kindex C-M-% @findex query-replace-regexp Aside from querying, @code{query-replace} works just like @code{replace-string}, and @code{query-replace-regexp} works just like @code{replace-regexp}. This command is run by @kbd{C-M-%}. The things you can type when you are shown an occurrence of @var{string} or a match for @var{regexp} are: @ignore @c Not worth it. @kindex SPC @r{(query-replace)} @kindex DEL @r{(query-replace)} @kindex , @r{(query-replace)} @kindex RET @r{(query-replace)} @kindex . @r{(query-replace)} @kindex ! @r{(query-replace)} @kindex ^ @r{(query-replace)} @kindex C-r @r{(query-replace)} @kindex C-w @r{(query-replace)} @kindex C-l @r{(query-replace)} @end ignore @c WideCommands @table @kbd @item @key{SPC} to replace the occurrence with @var{newstring}. @item @key{DEL} to skip to the next occurrence without replacing this one. @item , @r{(Comma)} to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, @key{DEL} and @key{SPC} are equivalent in this situation; both move to the next occurrence. You can type @kbd{C-r} at this point (see below) to alter the replaced text. You can also type @kbd{C-x u} to undo the replacement; this exits the @code{query-replace}, so if you want to do further replacement you must use @kbd{C-x @key{ESC} @key{ESC} @key{RET}} to restart (@pxref{Repetition}). @item @key{RET} to exit without doing any more replacements. @item .@: @r{(Period)} to replace this occurrence and then exit without searching for more occurrences. @item ! to replace all remaining occurrences without asking again. @item ^ to go back to the position 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 @kbd{^} in a row is meaningful, because only one previous replacement position is kept during @code{query-replace}. @item C-r to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with @var{newstring}. When you are done, exit the recursive editing level with @kbd{C-M-c} to proceed to the next occurrence. @xref{Recursive Edit}. @item C-w to delete the occurrence, and then enter a recursive editing level as in @kbd{C-r}. Use the recursive edit to insert text to replace the deleted occurrence of @var{string}. When done, exit the recursive editing level with @kbd{C-M-c} to proceed to the next occurrence. @item C-l to redisplay the screen. Then you must type another character to specify what to do with this occurrence. @item C-h to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence. @end table Some other characters are aliases for the ones listed above: @kbd{y}, @kbd{n} and @kbd{q} are equivalent to @key{SPC}, @key{DEL} and @key{RET}. Aside from this, any other character exits the @code{query-replace}, and is then reread as part of a key sequence. Thus, if you type @kbd{C-k}, it exits the @code{query-replace} and then kills to end of line. To restart a @code{query-replace} once it is exited, use @kbd{C-x @key{ESC} @key{ESC}}, which repeats the @code{query-replace} because it used the minibuffer to read its arguments. @xref{Repetition, C-x ESC ESC}. See also @ref{Transforming File Names}, for Dired commands to rename, copy, or link files by replacing regexp matches in file names. @node Other Repeating Search,, Replace, Search @section 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, and all ignore case in matching, if the pattern contains no upper-case letters and @code{case-fold-search} is non-@code{nil}. @findex list-matching-lines @findex occur @findex count-matches @findex delete-non-matching-lines @findex delete-matching-lines @findex flush-lines @findex keep-lines @table @kbd @item M-x occur @key{RET} @var{regexp} @key{RET} Display a list showing each line in the buffer that contains a match for @var{regexp}. A numeric argument specifies the number of context lines to print before and after each matching line; the default is none. To limit the search to part of the buffer, narrow to that part (@pxref{Narrowing}). @kindex RET @r{(Occur mode)} The buffer @samp{*Occur*} containing the output serves as a menu for finding the occurrences in their original context. Click @kbd{Mouse-2} on an occurrence listed in @samp{*Occur*}, or position point there and type @key{RET}; this switches to the buffer that was searched and moves point to the original of the chosen occurrence. @item M-x list-matching-lines Synonym for @kbd{M-x occur}. @item M-x count-matches @key{RET} @var{regexp} @key{RET} Print the number of matches for @var{regexp} after point. @item M-x flush-lines @key{RET} @var{regexp} @key{RET} Delete each line that follows point and contains a match for @var{regexp}. @item M-x keep-lines @key{RET} @var{regexp} @key{RET} Delete each line that follows point and @emph{does not} contain a match for @var{regexp}. @end table In addition, you can use @code{grep} from Emacs to search a collection of files for matches for a regular expression, then visit the matches either sequentially or in arbitrary order. @xref{Grep Searching}.