@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. @c See the file elisp.texi for copying conditions. @setfilename ../info/searching @node Searching and Matching, Syntax Tables, Text, Top @chapter Searching and Matching @cindex searching GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the @dfn{match data} to determine which text matched the whole regular expression or various portions of it. @menu * String Search:: Search for an exact match. * Regular Expressions:: Describing classes of strings. * Regexp Search:: Searching for a match for a regexp. * Search and Replace:: Internals of @code{query-replace}. * Match Data:: Finding out which part of the text matched various parts of a regexp, after regexp search. * Searching and Case:: Case-independent or case-significant searching. * Standard Regexps:: Useful regexps for finding sentences, pages,... @end menu The @samp{skip-chars@dots{}} functions also perform a kind of searching. @xref{Skipping Characters}. @node String Search @section Searching for Strings @cindex string search These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; @var{limit} and @var{noerror} are set to @code{nil}, and @var{repeat} is set to 1. @deffn Command search-forward string &optional limit noerror repeat This function searches forward from point for an exact match for @var{string}. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on @var{noerror} (see below). @c Emacs 19 feature In the following example, point is initially at the beginning of the line. Then @code{(search-forward "fox")} moves point after the last letter of @samp{fox}: @example @group ---------- Buffer: foo ---------- @point{}The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- @end group @group (search-forward "fox") @result{} 20 ---------- Buffer: foo ---------- The quick brown fox@point{} jumped over the lazy dog. ---------- Buffer: foo ---------- @end group @end example The argument @var{limit} specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If @var{limit} is omitted or @code{nil}, it defaults to the end of the accessible portion of the buffer. @kindex search-failed What happens when the search fails depends on the value of @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} error is signaled. If @var{noerror} is @code{t}, @code{search-forward} returns @code{nil} and does nothing. If @var{noerror} is neither @code{nil} nor @code{t}, then @code{search-forward} moves point to the upper bound and returns @code{nil}. (It would be more consistent now to return the new position of point in that case, but some programs may depend on a value of @code{nil}.) If @var{repeat} is non-@code{nil}, then the search is repeated that many times. Point is positioned at the end of the last match. @end deffn @deffn Command search-backward string &optional limit noerror repeat This function searches backward from point for @var{string}. It is just like @code{search-forward} except that it searches backwards and leaves point at the beginning of the match. @end deffn @deffn Command word-search-forward string &optional limit noerror repeat @cindex word search This function searches forward from point for a ``word'' match for @var{string}. If it finds a match, it sets point to the end of the match found, and returns the new value of point. @c Emacs 19 feature Word matching regards @var{string} as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word @samp{ball} does not match the word @samp{balls}), but the details of punctuation and spacing are ignored (searching for @samp{ball boy} does match @samp{ball. Boy!}). In this example, point is initially at the beginning of the buffer; the search leaves it between the @samp{y} and the @samp{!}. @example @group ---------- Buffer: foo ---------- @point{}He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- @end group @group (word-search-forward "Please find the ball, boy.") @result{} 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy@point{}!" ---------- Buffer: foo ---------- @end group @end example If @var{limit} is non-@code{nil} (it must be a position in the current buffer), then it is the upper bound to the search. The match found must not extend after that position. If @var{noerror} is @code{nil}, then @code{word-search-forward} signals an error if the search fails. If @var{noerror} is @code{t}, then it returns @code{nil} instead of signaling an error. If @var{noerror} is neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the end of the buffer) and returns @code{nil}. If @var{repeat} is non-@code{nil}, then the search is repeated that many times. Point is positioned at the end of the last match. @end deffn @deffn Command word-search-backward string &optional limit noerror repeat This function searches backward from point for a word match to @var{string}. This function is just like @code{word-search-forward} except that it searches backward and normally leaves point at the beginning of the match. @end deffn @node Regular Expressions @section Regular Expressions @cindex regular expression @cindex regexp A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them. @menu * Syntax of Regexps:: Rules for writing regular expressions. * Regexp Example:: Illustrates regular expression syntax. @end menu @node Syntax of Regexps @subsection Syntax of Regular Expressions 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 character and nothing else. The special characters are @samp{$}, @samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, @samp{]} and @samp{\}; no new special characters will be defined in the future. 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}.@refill 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 more powerful, you need to use one of the special characters. Here is a list of them: @need 1200 @table @kbd @item .@: @r{(Period)} @cindex @samp{.} in regexp 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 * @cindex @samp{*} in regexp is not a construct by itself; it is a suffix operator that means to repeat the preceding regular expression as many times as possible. In @samp{fo*}, the @samp{*} applies to the @samp{o}, so @samp{fo*} matches one @samp{f} followed by any number of @samp{o}s. The case of zero @samp{o}s is allowed: @samp{fo*} does match @samp{f}.@refill @samp{*} always applies to the @emph{smallest} possible preceding expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating @samp{fo}.@refill 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 + @cindex @samp{+} in regexp is a suffix operator similar to @samp{*} except that the preceding expression must match 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 ? @cindex @samp{?} in regexp is a suffix operator similar to @samp{*} except that the preceding expression can match either once or not at all. For example, @samp{ca?r} matches @samp{car} or @samp{cr}, but does not match anyhing else. @item [ @dots{} ] @cindex character set (in regexp) @cindex @samp{[} in regexp @cindex @samp{]} in regexp @samp{[} begins a @dfn{character set}, which is terminated by a @samp{]}. In the simplest case, the characters between the two brackets form the set. 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.@refill The usual regular expression special characters are not special inside a character set. A completely different set of special characters exists inside character sets: @samp{]}, @samp{-} and @samp{^}.@refill @samp{-} is used for ranges of characters. To write a range, write two characters with a @samp{-} between them. Thus, @samp{[a-z]} matches any lower case letter. Ranges may be intermixed freely with individual characters, as in @samp{[a-z$%.]}, which matches any lower case letter or @samp{$}, @samp{%} or a period.@refill To include a @samp{]} in a character set, make it the first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. To include a @samp{-}, write @samp{-} as the first character in the set, or put immediately after a range. (You can replace one individual character @var{c} with the range @samp{@var{c}-@var{c}} to make a place to put the @samp{-}). There is no way to write a set containing just @samp{-} and @samp{]}. To include @samp{^} in a set, put it anywhere but at the beginning of the set. @item [^ @dots{} ] @cindex @samp{^} in regexp @samp{[^} begins a @dfn{complement character set}, which matches any character except the ones specified. Thus, @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and digits.@refill @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 (thus, @samp{-} and @samp{]} 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. @item ^ @cindex @samp{^} in regexp @cindex beginning of line in regexp 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} which occurs at the beginning of a line. When matching a string, @samp{^} matches at the beginning of the string or after a newline character @samp{\n}. @item $ @cindex @samp{$} in regexp is similar to @samp{^} but matches only at the end of a line. Thus, @samp{x+$} matches a string of one @samp{x} or more at the end of a line. When matching a string, @samp{$} matches at the end of the string or before a newline character @samp{\n}. @item \ @cindex @samp{\} in regexp has two functions: it quotes the special characters (including @samp{\}), and it introduces additional special constructs. Because @samp{\} quotes special characters, @samp{\$} is a regular expression which matches only @samp{$}, and @samp{\[} is a regular expression which matches only @samp{[}, and so on. Note that @samp{\} also has special meaning in the read syntax of Lisp strings (@pxref{String Type}), and must be quoted with @samp{\}. For example, the regular expression that matches the @samp{\} character is @samp{\\}. To write a Lisp string that contains the characters @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another @samp{\}. Therefore, the read syntax for a regular expression matching @samp{\} is @code{"\\\\"}.@refill @end table @strong{Please 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; 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: characters which, when preceded by @samp{\}, are special constructs. Such characters are always ordinary when encountered on their own. Here is a table of @samp{\} constructs: @table @kbd @item \| @cindex @samp{|} in regexp @cindex regexp alternative specifies an alternative. Two regular expressions @var{a} and @var{b} with @samp{\|} in between form an expression that matches anything that either @var{a} or @var{b} matches.@refill 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 \( @dots{} \) @cindex @samp{(} in regexp @cindex @samp{)} in regexp @cindex regexp grouping 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 an expression for a suffix operator such as @samp{*} to act 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 which happens to be assigned as a second meaning to the same @samp{\( @dots{} \)} construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature: @item \@var{digit} matches the same text which matched the @var{digit}th occurrence of a @samp{\( @dots{} \)} construct. In other words, 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 @var{digit} to match that same text, whatever it may have been. 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. @item \w @cindex @samp{\w} in regexp matches any word-constituent character. The editor syntax table determines which characters these are. @xref{Syntax Tables}. @item \W @cindex @samp{\W} in regexp matches any character that is not a word-constituent. @item \s@var{code} @cindex @samp{\s} in regexp matches any character whose syntax is @var{code}. Here @var{code} is a character which represents a syntax code: thus, @samp{w} for word constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, etc. @xref{Syntax Tables}, for a list of syntax codes and the characters that stand for them. @item \S@var{code} @cindex @samp{\S} in regexp matches any character whose syntax is not @var{code}. @end table These regular expression constructs match the empty string---that is, they don't use up any characters---but whether they match depends on the context. @table @kbd @item \` @cindex @samp{\`} in regexp matches the empty string, but only at the beginning of the buffer or string being matched against. @item \' @cindex @samp{\'} in regexp matches the empty string, but only at the end of the buffer or string being matched against. @item \= @cindex @samp{\=} in regexp matches the empty string, but only at point. (This construct is not defined when matching against a string.) @item \b @cindex @samp{\b} in regexp 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 @item \B @cindex @samp{\B} in regexp matches the empty string, but @emph{not} at the beginning or end of a word. @item \< @cindex @samp{\<} in regexp matches the empty string, but only at the beginning of a word. @item \> @cindex @samp{\>} in regexp matches the empty string, but only at the end of a word. @end table @kindex invalid-regexp Not every string is a valid regular expression. For example, a string with unbalanced square brackets is invalid (with a few exceptions, such as @samp{[]]}, and so is a string that ends with a single @samp{\}. If an invalid regular expression is passed to any of the search functions, an @code{invalid-regexp} error is signaled. @defun regexp-quote string This function returns a regular expression string that matches exactly @var{string} and nothing else. This allows you to request an exact string match when calling a function that wants a regular expression. @example @group (regexp-quote "^The cat$") @result{} "\\^The cat\\$" @end group @end example One use of @code{regexp-quote} is to combine an exact string match with context described as a regular expression. For example, this searches for the string which is the value of @code{string}, surrounded by whitespace: @example @group (re-search-forward (concat "\\s " (regexp-quote string) "\\s ")) @end group @end example @end defun @node Regexp Example @comment node-name, next, previous, up @subsection Complex Regexp Example Here is a complicated regexp, used by Emacs to recognize the end of a sentence together with any whitespace that follows. It is the value of the variable @code{sentence-end}. First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. @samp{\"} stands for a double-quote as part of the string, @samp{\\} for a backslash as part of the string, @samp{\t} for a tab and @samp{\n} for a newline. @example "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" @end example In contrast, if you evaluate the variable @code{sentence-end}, you will see the following: @example @group sentence-end @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[ ]*" @end group @end example @noindent In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: @table @code @item [.?!] The first part of the pattern consists of three characters, a period, a question mark and an exclamation mark, within square brackets. The match must begin with one of these three characters. @item []\"')@}]* The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in a string. The @samp{*} at the end indicates that the immediately preceding regular expression (a character set, in this case) may be repeated zero or more times. @item \\($\\|@ \\|\t\\|@ @ \\) The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line, or a tab, or two spaces. The double backslashes mark the parentheses and vertical bars as regular expression syntax; the parentheses mark the group and the vertical bars separate alternatives. The dollar sign is used to match the end of a line. @item [ \t\n]* Finally, the last part of the pattern matches any additional whitespace beyond the minimum needed to end a sentence. @end table @node Regexp Search @section Regular Expression Searching @cindex regular expression searching @cindex regexp searching @cindex searching for regexp In GNU Emacs, you can search for the next match for a regexp either incrementally or not. For incremental search commands, see @ref{Regexp Search, , Regular Expression Search, emacs, The GNU Emacs Manual}. Here we describe only the search functions useful in programs. The principal one is @code{re-search-forward}. @deffn Command re-search-forward regexp &optional limit noerror repeat This function searches forward in the current buffer for a string of text that is matched by the regular expression @var{regexp}. The function skips over any amount of text that is not matched by @var{regexp}, and leaves point at the end of the first match found. It returns the new value of point. If @var{limit} is non-@code{nil} (it must be a position in the current buffer), then it is the upper bound to the search. No match extending after that position is accepted. What happens when the search fails depends on the value of @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} error is signaled. If @var{noerror} is @code{t}, @code{re-search-forward} does nothing and returns @code{nil}. If @var{noerror} is neither @code{nil} nor @code{t}, then @code{re-search-forward} moves point to @var{limit} (or the end of the buffer) and returns @code{nil}. If @var{repeat} is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails. In the following example, point is initially before the @samp{T}. Evaluating the search call moves point to the end of that line (between the @samp{t} of @samp{hat} and the newline). @example @group ---------- Buffer: foo ---------- I read "@point{}The cat in the hat comes back" twice. ---------- Buffer: foo ---------- @end group @group (re-search-forward "[a-z]+" nil t 5) @result{} 27 ---------- Buffer: foo ---------- I read "The cat in the hat@point{} comes back" twice. ---------- Buffer: foo ---------- @end group @end example @end deffn @deffn Command re-search-backward regexp &optional limit noerror repeat This function searches backward in the current buffer for a string of text that is matched by the regular expression @var{regexp}, leaving point at the beginning of the first text found. This function is analogous to @code{re-search-forward}, but they are not simple mirror images. @code{re-search-forward} finds the match whose beginning is as close as possible. If @code{re-search-backward} were a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible. The reason is that matching a regular expression at a given spot always works from beginning to end, and is done at a specified beginning position. A true mirror-image of @code{re-search-forward} would require a special feature for matching regexps from end to beginning. It's not worth the trouble of implementing that. @end deffn @defun string-match regexp string &optional start This function returns the index of the start of the first match for the regular expression @var{regexp} in @var{string}, or @code{nil} if there is no match. If @var{start} is non-@code{nil}, the search starts at that index in @var{string}. For example, @example @group (string-match "quick" "The quick brown fox jumped quickly.") @result{} 4 @end group @group (string-match "quick" "The quick brown fox jumped quickly." 8) @result{} 27 @end group @end example @noindent The index of the first character of the string is 0, the index of the second character is 1, and so on. After this function returns, the index of the first character beyond the match is available as @code{(match-end 0)}. @xref{Match Data}. @example @group (string-match "quick" "The quick brown fox jumped quickly." 8) @result{} 27 @end group @group (match-end 0) @result{} 32 @end group @end example @end defun @defun looking-at regexp This function determines whether the text in the current buffer directly following point matches the regular expression @var{regexp}. ``Directly following'' means precisely that: the search is ``anchored'' and it can succeed only starting with the first character following point. The result is @code{t} if so, @code{nil} otherwise. This function does not move point, but it updates the match data, which you can access using @code{match-beginning} and @code{match-end}. @xref{Match Data}. In this example, point is located directly before the @samp{T}. If it were anywhere else, the result would be @code{nil}. @example @group ---------- Buffer: foo ---------- I read "@point{}The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") @result{} t @end group @end example @end defun @ignore @deffn Command delete-matching-lines regexp This function is identical to @code{delete-non-matching-lines}, save that it deletes what @code{delete-non-matching-lines} keeps. In the example below, point is located on the first line of text. @example @group ---------- Buffer: foo ---------- We hold these truths to be self-evident, that all men are created equal, and that they are ---------- Buffer: foo ---------- @end group @group (delete-matching-lines "the") @result{} nil ---------- Buffer: foo ---------- to be self-evident, that all men are created ---------- Buffer: foo ---------- @end group @end example @end deffn @deffn Command flush-lines regexp This function is the same as @code{delete-matching-lines}. @end deffn @defun delete-non-matching-lines regexp This function deletes all lines following point which don't contain a match for the regular expression @var{regexp}. @end defun @deffn Command keep-lines regexp This function is the same as @code{delete-non-matching-lines}. @end deffn @deffn Command how-many regexp This function counts the number of matches for @var{regexp} there are in the current buffer following point. It prints this number in the echo area, returning the string printed. @end deffn @deffn Command count-matches regexp This function is a synonym of @code{how-many}. @end deffn @deffn Command list-matching-lines regexp nlines This function is a synonym of @code{occur}. Show all lines following point containing a match for @var{regexp}. Display each line with @var{nlines} lines before and after, or @code{-}@var{nlines} before if @var{nlines} is negative. @var{nlines} defaults to @code{list-matching-lines-default-context-lines}. Interactively it is the prefix arg. The lines are shown in a buffer named @samp{*Occur*}. It serves as a menu to find any of the occurrences in this buffer. @kbd{C-h m} (@code{describe-mode} in that buffer gives help. @end deffn @defopt list-matching-lines-default-context-lines Default value is 0. Default number of context lines to include around a @code{list-matching-lines} match. A negative number means to include that many lines before the match. A positive number means to include that many lines both before and after. @end defopt @end ignore @node Search and Replace @section Search and Replace @cindex replacement @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map This function is the guts of @code{query-replace} and related commands. It searches for occurrences of @var{from-string} and replaces some or all of them. If @var{query-flag} is @code{nil}, it replaces all occurrences; otherwise, it asks the user what to do about each one. If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is considered a regular expression; otherwise, it must match literally. If @var{delimited-flag} is non-@code{nil}, then only replacements surrounded by word boundaries are considered. The argument @var{replacements} specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order. If @var{repeat-count} is non-@code{nil}, it should be an integer, the number of occurrences to consider. In this case, @code{perform-replace} returns after considering that many occurrences. Normally, the keymap @code{query-replace-map} defines the possible user responses. The argument @var{map}, if non-@code{nil}, is a keymap to use instead of @code{query-replace-map}. @end defun @defvar query-replace-map This variable holds a special keymap that defines the valid user responses for @code{query-replace} and related functions, as well as @code{y-or-n-p} and @code{map-y-or-n-p}. It is unusual in two ways: @itemize @bullet @item The ``key bindings'' are not commands, just symbols that are meaningful to the functions that use this map. @item Prefix keys are not supported; each key binding must be for a single event key sequence. This is because the functions don't use read key sequence to get the input; instead, they read a single event and look it up ``by hand.'' @end itemize @end defvar Here are the meaningful ``bindings'' for @code{query-replace-map}. Several of them are meaningful only for @code{query-replace} and friends. @table @code @item act Do take the action being considered---in other words, ``yes.'' @item skip Do not take action for this question---in other words, ``no.'' @item exit Answer this question ``no,'' and don't ask any more. @item act-and-exit Answer this question ``yes,'' and don't ask any more. @item act-and-show Answer this question ``yes,'' but show the results---don't advance yet to the next question. @item automatic Answer this question and all subsequent questions in the series with ``yes,'' without further user interaction. @item backup Move back to the previous place that a question was asked about. @item edit Enter a recursive edit to deal with this question---instead of any other action that would normally be taken. @item delete-and-edit Delete the text being considered, then enter a recursive edit to replace it. @item recenter Redisplay and center the window, then ask the same question again. @item quit Perform a quit right away. Only @code{y-or-n-p} and related functions use this answer. @item help Display some help, then ask again. @end table @node Match Data @section The Match Data @cindex match data Emacs keeps track of the positions of the start and end of segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and then extract parts of the match under control of the pattern. Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten. @menu * Simple Match Data:: Accessing single items of match data, such as where a particular subexpression started. * Replacing Match:: Replacing a substring that was matched. * Entire Match Data:: Accessing the entire match data at once, as a list. * Saving Match Data:: Saving and restoring the match data. @end menu @node Simple Match Data @subsection Simple Match Data Access This section explains how to use the match data to find the starting point or ending point of the text that was matched by a particular search, or by a particular parenthetical subexpression of a regular expression. @defun match-beginning count This function returns the position of the start of text matched by the last regular expression searched for, or a subexpression of it. The argument @var{count}, a number, specifies a subexpression whose start position is the value. If @var{count} is zero, then the value is the position of the text matched by the whole regexp. If @var{count} is greater than zero, then the value is the position of the beginning of the text matched by the @var{count}th subexpression. Subexpressions of a regular expression are those expressions grouped inside of parentheses, @samp{\(@dots{}\)}. The @var{count}th subexpression is found by counting occurrences of @samp{\(} from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. The value is @code{nil} for a parenthetical grouping inside of a @samp{\|} alternative that wasn't used in the match. @end defun @defun match-end count This function returns the position of the end of the text that matched the last regular expression searched for, or a subexpression of it. This function is otherwise similar to @code{match-beginning}. @end defun Here is an example of using the match data, with a comment showing the positions within the text: @example @group (string-match "\\(qu\\)\\(ick\\)" "The quick fox jumped quickly.") ;0123456789 @result{} 4 @end group @group (match-beginning 1) ; @r{The beginning of the match} @result{} 4 ; @r{with @samp{qu} is at index 4.} @end group @group (match-beginning 2) ; @r{The beginning of the match} @result{} 6 ; @r{with @samp{ick} is at index 6.} @end group @group (match-end 1) ; @r{The end of the match} @result{} 6 ; @r{with @samp{qu} is at index 6.} (match-end 2) ; @r{The end of the match} @result{} 9 ; @r{with @samp{ick} is at index 9.} @end group @end example Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word @samp{in}. The beginning of the entire match is at the 9th character of the buffer (@samp{T}), and the beginning of the match for the first subexpression is at the 13th character (@samp{c}). @example @group (list (re-search-forward "The \\(cat \\)") (match-beginning 0) (match-beginning 1)) @result{} (t 9 13) @end group @group ---------- Buffer: foo ---------- I read "The cat @point{}in the hat comes back" twice. ^ ^ 9 13 ---------- Buffer: foo ---------- @end group @end example @noindent (In this case, the index returned is a buffer position; the first character of the buffer counts as 1.) @node Replacing Match @subsection Replacing the Text That Matched This function replaces the text matched by the last search with @var{replacement}. @cindex case in replacements @defun replace-match replacement &optional fixedcase literal This function replaces the buffer text matched by the last search, with @var{replacement}. It applies only to buffers; you can't use @code{replace-match} to replace a substring found with @code{string-match}. If @var{fixedcase} is non-@code{nil}, then the case of the replacement text is not changed; otherwise, the replacement text is converted to a different case depending upon the capitalization of the text to be replaced. If the original text is all upper case, the replacement text is converted to upper case. If the first word of the original text is capitalized, then the first word of the replacement text is capitalized. If the original text contains just one word, and that word is a capital letter, @code{replace-match} considers this a capitalized first word rather than all upper case. If @var{literal} is non-@code{nil}, then @var{replacement} is inserted exactly as it is, the only alterations being case changes as needed. If it is @code{nil} (the default), then the character @samp{\} is treated specially. If a @samp{\} appears in @var{replacement}, then it must be part of one of the following sequences: @table @asis @item @samp{\&} @cindex @samp{&} in replacement @samp{\&} stands for the entire text being replaced. @item @samp{\@var{n}} @cindex @samp{\@var{n}} in replacement @samp{\@var{n}} stands for the text that matched the @var{n}th subexpression in the original regexp. Subexpressions are those expressions grouped inside of @samp{\(@dots{}\)}. @var{n} is a digit. @item @samp{\\} @cindex @samp{\} in replacement @samp{\\} stands for a single @samp{\} in the replacement text. @end table @code{replace-match} leaves point at the end of the replacement text, and returns @code{t}. @end defun @node Entire Match Data @subsection Accessing the Entire Match Data The functions @code{match-data} and @code{set-match-data} read or write the entire match data, all at once. @defun match-data This function returns a newly constructed list containing all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element @ifinfo number 2@var{n} @end ifinfo @tex number {\mathsurround=0pt $2n$} @end tex corresponds to @code{(match-beginning @var{n})}; and element @ifinfo number 2@var{n} + 1 @end ifinfo @tex number {\mathsurround=0pt $2n+1$} @end tex corresponds to @code{(match-end @var{n})}. All the elements are markers or @code{nil} if matching was done on a buffer, and all are integers or @code{nil} if matching was done on a string with @code{string-match}. (In Emacs 18 and earlier versions, markers were used even for matching on a string, except in the case of the integer 0.) As always, there must be no possibility of intervening searches between the call to a search function and the call to @code{match-data} that is intended to access the match data for that search. @example @group (match-data) @result{} (# # # #) @end group @end example @end defun @defun set-match-data match-list This function sets the match data from the elements of @var{match-list}, which should be a list that was the value of a previous call to @code{match-data}. If @var{match-list} refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way. @findex store-match-data @code{store-match-data} is an alias for @code{set-match-data}. @end defun @node Saving Match Data @subsection Saving and Restoring the Match Data All asynchronous process functions (filters and sentinels) and functions that use @code{recursive-edit} should save and restore the match data if they do a search or if they let the user type arbitrary commands. Saving the match data is useful in other cases as well---whenever you want to access the match data resulting from an earlier search, notwithstanding another intervening search. This example shows the problem that can arise if you fail to attend to this requirement: @example @group (re-search-forward "The \\(cat \\)") @result{} 48 (foo) ; @r{Perhaps @code{foo} does} ; @r{more searching.} (match-end 0) @result{} 61 ; @r{Unexpected result---not 48!} @end group @end example In Emacs versions 19 and later, you can save and restore the match data with @code{save-match-data}: @defspec save-match-data body@dots{} This special form executes @var{body}, saving and restoring the match data around it. This is useful if you wish to do a search without altering the match data that resulted from an earlier search. @end defspec You can use @code{set-match-data} together with @code{match-data} to imitate the effect of the special form @code{save-match-data}. This is useful for writing code that can run in Emacs 18. Here is how: @example @group (let ((data (match-data))) (unwind-protect @dots{} ; @r{May change the original match data.} (set-match-data data))) @end group @end example @ignore Here is a function which restores the match data provided the buffer associated with it still exists. @smallexample @group (defun restore-match-data (data) @c It is incorrect to split the first line of a doc string. @c If there's a problem here, it should be solved in some other way. "Restore the match data DATA unless the buffer is missing." (catch 'foo (let ((d data)) @end group (while d (and (car d) (null (marker-buffer (car d))) @group ;; @file{match-data} @r{buffer is deleted.} (throw 'foo nil)) (setq d (cdr d))) (set-match-data data)))) @end group @end smallexample @end ignore @node Searching and Case @section Searching and Case @cindex searching and case By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for @samp{FOO}, then @samp{Foo} or @samp{foo} is also considered a match. Regexps, and in particular character sets, are included: thus, @samp{[aB]} would match @samp{a} or @samp{A} or @samp{b} or @samp{B}. If you do not want this feature, set the variable @code{case-fold-search} to @code{nil}. Then all letters must match exactly, including case. This is a per-buffer-local variable; altering the variable affects only the current buffer. (@xref{Intro to Buffer-Local}.) Alternatively, you may change the value of @code{default-case-fold-search}, which is the default value of @code{case-fold-search} for buffers that do not override it. Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions Lisp functions use. @defopt case-replace This variable determines whether @code{query-replace} should preserve case in replacements. If the variable is @code{nil}, then @code{replace-match} should not try to convert case. @end defopt @defopt case-fold-search This buffer-local variable determines whether searches should ignore case. If the variable is @code{nil} they do not ignore case; otherwise they do ignore case. @end defopt @defvar default-case-fold-search The value of this variable is the default value for @code{case-fold-search} in buffers that do not override it. This is the same as @code{(default-value 'case-fold-search)}. @end defvar @node Standard Regexps @section Standard Regular Expressions Used in Editing @cindex regexps used standardly in editing @cindex standard regexps used in editing This section describes some variables that hold regular expressions used for certain purposes in editing: @defvar page-delimiter This is the regexp describing line-beginnings that separate pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or @code{"^\C-l"}). @end defvar @defvar paragraph-separate This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change @code{paragraph-start} also.) The default value is @code{"^[ \t\f]*$"}, which is a line that consists entirely of spaces, tabs, and form feeds. @end defvar @defvar paragraph-start This is the regular expression for recognizing the beginning of a line that starts @emph{or} separates paragraphs. The default value is @code{"^[ \t\n\f]"}, which matches a line starting with a space, tab, newline, or form feed. @end defvar @defvar sentence-end This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is: @example "[.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*" @end example This means a period, question mark or exclamation mark, followed by a closing brace, followed by tabs, spaces or new lines. For a detailed explanation of this regular expression, see @ref{Regexp Example}. @end defvar