@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. @c See the file elisp.texi for copying conditions. @setfilename ../info/searching @node Searching and Matching, Syntax Tables, Non-ASCII Characters, 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. * POSIX Regexps:: Searching POSIX-style for the longest match. * 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. These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. @xref{Text Representations}. @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 existing programs may depend on a value of @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. @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 that 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 that 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 800 @table @asis @item @samp{.}@: @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 @samp{*} @cindex @samp{*} in regexp 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 the hope that that will make 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 Nested repetition operators can be extremely slow if they specify backtracking loops. For example, it could take hours for the regular expression @samp{\(x+y*\)*a} to try to match the sequence @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately fails. The slowness is because Emacs must try each imaginable way of grouping the 35 @samp{x}s before concluding that none of them can work. To make sure your regular expressions run fast, check nested repetitions carefully. @item @samp{+} @cindex @samp{+} in regexp 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 @samp{?} @cindex @samp{?} in regexp is a postfix operator, similar to @samp{*} except that it must match the preceding expression either once or not at all. For example, @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. @item @samp{[ @dots{} ]} @cindex character alternative (in regexp) @cindex @samp{[} in regexp @cindex @samp{]} in regexp is a @dfn{character alternative}, which begins with @samp{[} and is terminated by @samp{]}. In the simplest case, the characters between the two brackets are what this character alternative 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 alternative, by writing the starting and ending characters with a @samp{-} between them. Thus, @samp{[a-z]} matches any lower-case @sc{ASCII} letter. Ranges may be intermixed freely with individual characters, as in @samp{[a-z$%.]}, which matches any lower case @sc{ASCII} letter or @samp{$}, @samp{%} or period. You cannot always match all non-@sc{ASCII} characters with the regular expression @samp{[\200-\377]}. This works when searching a unibyte buffer or string (@pxref{Text Representations}), but not in a multibyte buffer or string, because many non-@sc{ASCII} characters have codes above octal 0377. However, the regular expression @samp{[^\000-\177]} does match all non-@sc{ASCII} characters, in both multibyte and unibyte representations, because only the @sc{ASCII} characters are excluded. The beginning and end of a range must be in the same character set (@pxref{Character Sets}). Thus, @samp{[a-\x8e0]} is invalid because @samp{a} is in the @sc{ASCII} character set but the character 0x8e0 (@samp{a} with grave accent) is in the Emacs character set for Latin-1. Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. To include a @samp{]} in a character alternative, 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 character alternative, or put it after a range. Thus, @samp{[]-]} matches both @samp{]} and @samp{-}. To include @samp{^} in a character alternative, put it anywhere but at the beginning. @item @samp{[^ @dots{} ]} @cindex @samp{^} in regexp @samp{[^} begins a @dfn{complemented character alternative}, 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 alternative 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 alternative 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 @samp{^} @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} that occurs at the beginning of a line. When matching a string instead of a buffer, @samp{^} matches at the beginning of the string or after a newline character @samp{\n}. @item @samp{$} @cindex @samp{$} in regexp is similar to @samp{^} but matches only at the end of a line. Thus, @samp{x+$} matches a string of one @samp{x} or more at the end of a line. When matching a string instead of a buffer, @samp{$} matches at the end of the string or before a newline character @samp{\n}. @item @samp{\} @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 that matches only @samp{$}, and @samp{\[} is a regular expression that 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; 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{\} which have special meanings. (The second character in such a sequence is always ordinary when used on its own.) Here is a table of @samp{\} constructs. @table @samp @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, the regular expression @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{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any number (zero or more) of @samp{na} strings. @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 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 that 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 that represents a syntax code: thus, @samp{w} for word constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, etc. To represent whitespace syntax, use either @samp{-} or a space character. @xref{Syntax Class Table}, 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 The following 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 @samp @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 @samp{\b} matches at the beginning or end of the buffer regardless of what text appears next to it. @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. @samp{\<} matches at the beginning of the buffer only if a word-constituent character follows. @item \> @cindex @samp{\>} in regexp 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. @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 that is the value of @var{string}, surrounded by whitespace: @example @group (re-search-forward (concat "\\s-" (regexp-quote string) "\\s-")) @end group @end example @end defun @defun regexp-opt strings &optional paren @tindex regexp-opt This function returns an efficient regular expression that will match any of the strings @var{strings}. This is useful when you need to make matching or searching as fast as possible---for example, for Font Lock mode. If the optional argument @var{paren} is non-@code{nil}, then the returned regular expression is always enclosed by at least one parentheses-grouping construct. This simplified definition of @code{regexp-opt} produces a regular expression which is equivalent to the actual value (but not as efficient): @example (defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren))) @end example @end defun @defun regexp-opt-depth regexp @tindex regexp-opt-depth This function returns the total number of grouping constructs (parenthesized expressions) in @var{regexp}. @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 "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" @end example @noindent In contrast, if you evaluate the variable @code{sentence-end}, you will see the following: @example @group sentence-end @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[ ]*" @end group @end example @noindent In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: @table @code @item [.?!] The first part of the pattern is a character alternative that matches any one of three characters: period, question mark, and exclamation mark. The match must begin with one of these three characters. @item []\"')@}]* The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in a string. The @samp{*} at the end indicates that the immediately preceding regular expression (a character alternative, in this case) may be repeated zero or more times. @item \\($\\|@ $\\|\t\\|@ @ \\) The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line (optionally with a space), or a tab, or two spaces. The double backslashes mark the parentheses and vertical bars as regular expression syntax; the parentheses delimit a 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 regular expression 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}. These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. @xref{Text Representations}. @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. 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 all these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the function fails. What happens when the function 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}. 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 to the starting point. 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 starts at a specified beginning position. A true mirror-image of @code{re-search-forward} would require a special feature for matching regular expressions 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 @node POSIX Regexps @section POSIX Regular Expression Searching The usual regular expression functions do backtracking when necessary to handle the @samp{\|} and repetition constructs, but they continue this only until they find @emph{some} match. Then they succeed and report the first match found. This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match. @defun posix-search-forward regexp &optional limit noerror repeat This is like @code{re-search-forward} except that it performs the full backtracking specified by the POSIX standard for regular expression matching. @end defun @defun posix-search-backward regexp &optional limit noerror repeat This is like @code{re-search-backward} except that it performs the full backtracking specified by the POSIX standard for regular expression matching. @end defun @defun posix-looking-at regexp This is like @code{looking-at} except that it performs the full backtracking specified by the POSIX standard for regular expression matching. @end defun @defun posix-string-match regexp string &optional start This is like @code{string-match} except that it performs the full backtracking specified by the POSIX standard for regular expression matching. @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. Then it specifies how many times to use each of the strings in the @var{replacements} list before advancing cyclicly to the next one. Normally, the keymap @code{query-replace-map} defines the possible user responses for queries. 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 @code{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 give up on the entire series of questions, assuming that the answers will be ``no.'' @item act-and-exit Answer this question ``yes,'' and give up on the entire series of questions, assuming that subsequent answers will be ``no.'' @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 * Replacing Match:: Replacing a substring that was matched. * Simple Match Data:: Accessing single items of match data, such as where a particular subexpression started. * 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 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 string subexp This function replaces the text in the buffer (or in @var{string}) that was matched by the last search. It replaces that text with @var{replacement}. If you did the last search in a buffer, you should specify @code{nil} for @var{string}. Then @code{replace-match} does the replacement by editing the buffer; it leaves point at the end of the replacement text, and returns @code{t}. If you did the search in a string, pass the same string as @var{string}. Then @code{replace-match} does the replacement by constructing and returning a new string. 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 @code{case-replace} is @code{nil}, then case conversion is not done, regardless of the value of @var{fixed-case}. @xref{Searching and 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}}, where @var{n} is a digit, stands for the text that matched the @var{n}th subexpression in the original regexp. Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. @item @samp{\\} @cindex @samp{\} in replacement @samp{\\} stands for a single @samp{\} in the replacement text. @end table If @var{subexp} is non-@code{nil}, that says to replace just subexpression number @var{subexp} of the regexp that was matched, not the entire match. For example, after matching @samp{foo \(ba*r\)}, calling @code{replace-match} with 1 as @var{subexp} means to replace just the text that matched @samp{\(ba*r\)}. @end defun @node Simple Match Data @subsection Simple Match Data Access This section explains how to use the match data to find out what was matched by the last search or match operation. You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The @var{count} argument in the functions below specifies which. If @var{count} is zero, you are asking about the entire match. If @var{count} is positive, it specifies which subexpression you want. Recall that the subexpressions of a regular expression are those expressions grouped with escaped 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. Only regular expressions can have subexpressions---after a simple string search, the only information available is about the entire match. A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future. @defun match-string count &optional in-string This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if @var{count} is zero, or just the portion corresponding to the @var{count}th parenthetical subexpression, if @var{count} is positive. If @var{count} is out of range, or if that subexpression didn't match anything, the value is @code{nil}. If the last such operation was done against a string with @code{string-match}, then you should pass the same string as the argument @var{in-string}. After a buffer search or match, you should omit @var{in-string} or pass @code{nil} for it; but you should make sure that the current buffer when you call @code{match-string} is the one in which you did the searching or matching. @end defun @defun match-string-no-properties count This function is like @code{match-string} except that the result has no text properties. @end defun @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. If @var{count} is zero, then the value is the position of the start of the entire match. Otherwise, @var{count} specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression. The value is @code{nil} for a subexpression inside a @samp{\|} alternative that wasn't used in the match. @end defun @defun match-end count This function is like @code{match-beginning} except that it returns the position of the end of the match, rather than the position of the 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-string 0 "The quick fox jumped quickly.") @result{} "quick" (match-string 1 "The quick fox jumped quickly.") @result{} "qu" (match-string 2 "The quick fox jumped quickly.") @result{} "ick" @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{} (9 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 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}. 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 a semi-obsolete alias for @code{set-match-data}. @end defun @node Saving Match Data @subsection Saving and Restoring the Match Data When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data: @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 You can save and restore the match data with @code{save-match-data}: @defmac save-match-data body@dots{} This macro executes @var{body}, saving and restoring the match data around it. @end defmac You could use @code{set-match-data} together with @code{match-data} to imitate the effect of the special form @code{save-match-data}. Here is how: @example @group (let ((data (match-data))) (unwind-protect @dots{} ; @r{Ok to change the original match data.} (set-match-data data))) @end group @end example Emacs automatically saves and restores the match data when it runs process filter functions (@pxref{Filter Functions}) and process sentinels (@pxref{Sentinels}). @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. This applies to regular expressions, too; 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 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 used in Lisp code. @defopt case-replace This variable determines whether the replacement functions should preserve case. If the variable is @code{nil}, that means to use the replacement text verbatim. A non-@code{nil} value means to convert the case of the replacement text according to the text being replaced. The function @code{replace-match} is where this variable actually has its effect. @xref{Replacing Match}. @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 regular expression describing line-beginnings that separate pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or @code{"^\C-l"}); this matches a line that starts with a formfeed character. @end defvar The following two regular expressions should @emph{not} assume the match always starts at the beginning of a line; they should not use @samp{^} to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that @samp{^} would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a @samp{^} would be incorrect. However, a @samp{^} is harmless in modes where a left margin is never used. @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 @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin). @end defvar @defvar paragraph-start This is the regular expression for recognizing the beginning of a line that starts @emph{or} separates paragraphs. The default value is @w{@code{"[@ \t\n\f]"}}, which matches a line starting with a space, tab, newline, or form feed (after its left margin). @end defvar @defvar sentence-end This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is: @example "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" @end example This means a period, question mark or exclamation mark, followed optionally by a closing parenthetical character, followed by tabs, spaces or new lines. For a detailed explanation of this regular expression, see @ref{Regexp Example}. @end defvar