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[Emacs-diffs] Changes to searching.texi
|
From: |
Glenn Morris |
|
Subject: |
[Emacs-diffs] Changes to searching.texi |
|
Date: |
Thu, 06 Sep 2007 04:22:53 +0000 |
CVSROOT: /sources/emacs
Module name: emacs
Changes by: Glenn Morris <gm> 07/09/06 04:22:53
Index: searching.texi
===================================================================
RCS file: searching.texi
diff -N searching.texi
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ searching.texi 6 Sep 2007 04:22:53 -0000 1.1
@@ -0,0 +1,1766 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999,
2001,
address@hidden 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation,
Inc.
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/searching
address@hidden Searching and Matching, Syntax Tables, Non-ASCII Characters, Top
address@hidden Searching and Matching
address@hidden 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.
+
address@hidden
+* String Search:: Search for an exact match.
+* Searching and Case:: Case-independent or case-significant searching.
+* Regular Expressions:: Describing classes of strings.
+* Regexp Search:: Searching for a match for a regexp.
+* POSIX Regexps:: Searching POSIX-style for the longest match.
+* Match Data:: Finding out which part of the text matched,
+ after a string or regexp search.
+* Search and Replace:: Commands that loop, searching and replacing.
+* Standard Regexps:: Useful regexps for finding sentences, pages,...
address@hidden menu
+
+ The @address@hidden functions also perform a kind of searching.
address@hidden Characters}. To search for changes in character
+properties, see @ref{Property Search}.
+
address@hidden String Search
address@hidden Searching for Strings
address@hidden 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; the
+arguments @var{limit} and @var{noerror} are @code{nil}, and @var{repeat}
+is 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}.
+
address@hidden Command search-forward string &optional limit noerror repeat
+This function searches forward from point for an exact match for
address@hidden 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).
address@hidden 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}:
+
address@hidden
address@hidden
+---------- Buffer: foo ----------
address@hidden quick brown fox jumped over the lazy dog.
+---------- Buffer: foo ----------
address@hidden group
+
address@hidden
+(search-forward "fox")
+ @result{} 20
+
+---------- Buffer: foo ----------
+The quick brown address@hidden jumped over the lazy dog.
+---------- Buffer: foo ----------
address@hidden group
address@hidden 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.
+
address@hidden search-failed
+What happens when the search fails depends on the value of
address@hidden 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
address@hidden 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}.)
+
+The argument @var{noerror} only affects valid searches which fail to
+find a match. Invalid arguments cause errors regardless of
address@hidden
+
+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, with results depending on the value of
address@hidden, as described above.
address@hidden deffn
+
address@hidden 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.
address@hidden deffn
+
address@hidden Command word-search-forward string &optional limit noerror repeat
address@hidden @cindex word search Redundant
+This function searches forward from point for a ``word'' match for
address@hidden If it finds a match, it sets point to the end of the
+match found, and returns the new value of point.
address@hidden 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{!}.
+
address@hidden
address@hidden
+---------- Buffer: foo ----------
address@hidden said "Please! Find
+the ball boy!"
+---------- Buffer: foo ----------
address@hidden group
+
address@hidden
+(word-search-forward "Please find the ball, boy.")
+ @result{} 35
+
+---------- Buffer: foo ----------
+He said "Please! Find
+the ball address@hidden"
+---------- Buffer: foo ----------
address@hidden group
address@hidden example
+
+If @var{limit} is address@hidden, it must be a position in the current
+buffer; it specifies 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 accessible portion of the buffer) and returns @code{nil}.
+
+If @var{repeat} is address@hidden, then the search is repeated that many
+times. Point is positioned at the end of the last match.
address@hidden deffn
+
address@hidden Command word-search-backward string &optional limit noerror
repeat
+This function searches backward from point for a word match to
address@hidden This function is just like @code{word-search-forward}
+except that it searches backward and normally leaves point at the
+beginning of the match.
address@hidden deffn
+
address@hidden Searching and Case
address@hidden Searching and Case
address@hidden 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
address@hidden or @samp{foo} is also considered a match. This applies to
+regular expressions, too; thus, @samp{[aB]} would match @samp{a} or
address@hidden or @samp{b} or @samp{B}.
+
+ If you do not want this feature, set the variable
address@hidden 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
address@hidden, which is the default value of
address@hidden 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.
+
address@hidden case-replace
+This variable determines whether the higher level replacement
+functions should preserve case. If the variable is @code{nil}, that
+means to use the replacement text verbatim. A address@hidden value
+means to convert the case of the replacement text according to the
+text being replaced.
+
+This variable is used by passing it as an argument to the function
address@hidden @xref{Replacing Match}.
address@hidden defopt
+
address@hidden 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.
address@hidden defopt
+
address@hidden default-case-fold-search
+The value of this variable is the default value for
address@hidden in buffers that do not override it. This is the
+same as @code{(default-value 'case-fold-search)}.
address@hidden defvar
+
address@hidden Regular Expressions
address@hidden Regular Expressions
address@hidden regular expression
address@hidden 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.
+
address@hidden re-builder
address@hidden regular expressions, developing
+ For convenient interactive development of regular expressions, you
+can use the @kbd{M-x re-builder} command. It provides a convenient
+interface for creating regular expressions, by giving immediate visual
+feedback in a separate buffer. As you edit the regexp, all its
+matches in the target buffer are highlighted. Each parenthesized
+sub-expression of the regexp is shown in a distinct face, which makes
+it easier to verify even very complex regexps.
+
address@hidden
+* Syntax of Regexps:: Rules for writing regular expressions.
+* Regexp Example:: Illustrates regular expression syntax.
+* Regexp Functions:: Functions for operating on regular expressions.
address@hidden menu
+
address@hidden Syntax of Regexps
address@hidden 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{*},
address@hidden, @samp{?}, @samp{[}, @samp{^}, @samp{$}, and @samp{\}; no new
+special characters will be defined in the future. The character
address@hidden is special if it ends a character alternative (see later).
+The character @samp{-} is special inside a character alternative. A
address@hidden:} and balancing @samp{:]} enclose a character class inside a
+character alternative. 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
address@hidden and no other string. (It does @emph{not} match the string
address@hidden, but it does match a @emph{part} of that string.) Likewise,
address@hidden is a regular expression that matches only @address@hidden
+
+ 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 address@hidden
+
+ 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 regular expression constructs.
+
address@hidden
+* Regexp Special:: Special characters in regular expressions.
+* Char Classes:: Character classes used in regular expressions.
+* Regexp Backslash:: Backslash-sequences in regular expressions.
address@hidden menu
+
address@hidden Regexp Special
address@hidden Special Characters in Regular Expressions
+
+ Here is a list of the characters that are special in a regular
+expression.
+
address@hidden 800
address@hidden @asis
address@hidden @samp{.}@: @r{(Period)}
address@hidden @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
address@hidden@refill
+
address@hidden @samp{*}
address@hidden @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
address@hidden).
+
address@hidden always applies to the @emph{smallest} possible preceding
+expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating
address@hidden 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
address@hidden 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.
+
address@hidden:} Nested repetition operators can run for an
+indefinitely long time, if they lead to ambiguous matching. For
+example, trying to match the regular expression @samp{\(x+y*\)*a}
+against the string @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could
+take hours before it ultimately fails. Emacs must try each way of
+grouping the @samp{x}s before concluding that none of them can work.
+Even worse, @samp{\(x*\)*} can match the null string in infinitely
+many ways, so it causes an infinite loop. To avoid these problems,
+check nested repetitions carefully, to make sure that they do not
+cause combinatorial explosions in backtracking.
+
address@hidden @samp{+}
address@hidden @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
address@hidden, whereas @samp{ca*r} matches all three strings.
+
address@hidden @samp{?}
address@hidden @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,
address@hidden matches @samp{car} or @samp{cr}; nothing else.
+
address@hidden @samp{*?}, @samp{+?}, @samp{??}
+These are ``non-greedy'' variants of the operators @samp{*}, @samp{+}
+and @samp{?}. Where those operators match the largest possible
+substring (consistent with matching the entire containing expression),
+the non-greedy variants match the smallest possible substring
+(consistent with matching the entire containing expression).
+
+For example, the regular expression @samp{c[ad]*a} when applied to the
+string @samp{cdaaada} matches the whole string; but the regular
+expression @samp{c[ad]*?a}, applied to that same string, matches just
address@hidden (The smallest possible match here for @samp{[ad]*?} that
+permits the whole expression to match is @samp{d}.)
+
address@hidden @samp{[ @dots{} ]}
address@hidden character alternative (in regexp)
address@hidden @samp{[} in regexp
address@hidden @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
address@hidden 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 @acronym{ASCII} letter.
+Ranges may be intermixed freely with individual characters, as in
address@hidden, which matches any lower case @acronym{ASCII} letter
+or @samp{$}, @samp{%} or period.
+
+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.
+
+The beginning and end of a range of multibyte characters must be in
+the same character set (@pxref{Character Sets}). Thus,
address@hidden"[\x8e0-\x97c]"} is invalid because character 0x8e0 (@samp{a}
+with grave accent) is in the Emacs character set for Latin-1 but the
+character 0x97c (@samp{u} with diaeresis) is in the Emacs character
+set for Latin-2. (We use Lisp string syntax to write that example,
+and a few others in the next few paragraphs, in order to include hex
+escape sequences in them.)
+
+If a range starts with a unibyte character @var{c} and ends with a
+multibyte character @var{c2}, the range is divided into two parts: one
+is @address@hidden, the other is @address@hidden@var{c2}}, where
address@hidden is the first character of the charset to which @var{c2}
+belongs.
+
+You cannot always match all address@hidden characters with the regular
+expression @code{"[\200-\377]"}. This works when searching a unibyte
+buffer or string (@pxref{Text Representations}), but not in a multibyte
+buffer or string, because many address@hidden characters have codes
+above octal 0377. However, the regular expression @code{"[^\000-\177]"}
+does match all address@hidden characters (see below regarding @samp{^}),
+in both multibyte and unibyte representations, because only the
address@hidden characters are excluded.
+
+A character alternative can also specify named
+character classes (@pxref{Char Classes}). This is a POSIX feature whose
+syntax is @samp{[:@var{class}:]}. Using a character class is equivalent
+to mentioning each of the characters in that class; but the latter is
+not feasible in practice, since some classes include thousands of
+different characters.
+
address@hidden @samp{[^ @dots{} ]}
address@hidden @samp{^} in regexp
address@hidden begins a @dfn{complemented character alternative}. This
+matches any character except the ones specified. Thus,
address@hidden matches all characters @emph{except} letters and
+digits.
+
address@hidden 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}.
+
address@hidden @samp{^}
address@hidden beginning of line in regexp
+When matching a buffer, @samp{^} matches the empty string, but only at the
+beginning of a line in the text being matched (or the beginning of the
+accessible portion of the buffer). 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.
+
+For historical compatibility reasons, @samp{^} can be used only at the
+beginning of the regular expression, or after @samp{\(}, @samp{\(?:}
+or @samp{\|}.
+
address@hidden @samp{$}
address@hidden @samp{$} in regexp
address@hidden end of line in regexp
+is similar to @samp{^} but matches only at the end of a line (or the
+end of the accessible portion of the buffer). Thus, @samp{x+$}
+matches a string of one @samp{x} or more at the end of a line.
+
+When matching a string instead of a buffer, @samp{$} matches at the end
+of the string or before a newline character.
+
+For historical compatibility reasons, @samp{$} can be used only at the
+end of the regular expression, or before @samp{\)} or @samp{\|}.
+
address@hidden @samp{\}
address@hidden @samp{\} in regexp
+has two functions: it quotes the special characters (including
address@hidden), and it introduces additional special constructs.
+
+Because @samp{\} quotes special characters, @samp{\$} is a regular
+expression that matches only @samp{$}, and @samp{\[} is a regular
+expression that matches only @samp{[}, and so on.
+
+Note that @samp{\} also has special meaning in the read syntax of Lisp
+strings (@pxref{String Type}), and must be quoted with @samp{\}. For
+example, the regular expression that matches the @samp{\} character is
address@hidden To write a Lisp string that contains the characters
address@hidden, Lisp syntax requires you to quote each @samp{\} with another
address@hidden Therefore, the read syntax for a regular expression matching
address@hidden is @code{"\\\\"address@hidden
address@hidden table
+
address@hidden note:} For historical compatibility, special characters
+are treated as ordinary ones if they are in contexts where their special
+meanings make no sense. For example, @samp{*foo} treats @samp{*} as
+ordinary since there is no preceding expression on which the @samp{*}
+can act. It is poor practice to depend on this behavior; quote the
+special character anyway, regardless of where it address@hidden
+
+As a @samp{\} is not special inside a character alternative, it can
+never remove the special meaning of @samp{-} or @samp{]}. So you
+should not quote these characters when they have no special meaning
+either. This would not clarify anything, since backslashes can
+legitimately precede these characters where they @emph{have} special
+meaning, as in @samp{[^\]} (@code{"[^\\]"} for Lisp string syntax),
+which matches any single character except a backslash.
+
+In practice, most @samp{]} that occur in regular expressions close a
+character alternative and hence are special. However, occasionally a
+regular expression may try to match a complex pattern of literal
address@hidden and @samp{]}. In such situations, it sometimes may be
+necessary to carefully parse the regexp from the start to determine
+which square brackets enclose a character alternative. For example,
address@hidden consists of the complemented character alternative
address@hidden (which matches any single character that is not a square
+bracket), followed by a literal @samp{]}.
+
+The exact rules are that at the beginning of a regexp, @samp{[} is
+special and @samp{]} not. This lasts until the first unquoted
address@hidden, after which we are in a character alternative; @samp{[} is
+no longer special (except when it starts a character class) but @samp{]}
+is special, unless it immediately follows the special @samp{[} or that
address@hidden followed by a @samp{^}. This lasts until the next special
address@hidden that does not end a character class. This ends the character
+alternative and restores the ordinary syntax of regular expressions;
+an unquoted @samp{[} is special again and a @samp{]} not.
+
address@hidden Char Classes
address@hidden Character Classes
address@hidden character classes in regexp
+
+ Here is a table of the classes you can use in a character alternative,
+and what they mean:
+
address@hidden @samp
address@hidden [:ascii:]
+This matches any @acronym{ASCII} character (codes 0--127).
address@hidden [:alnum:]
+This matches any letter or digit. (At present, for multibyte
+characters, it matches anything that has word syntax.)
address@hidden [:alpha:]
+This matches any letter. (At present, for multibyte characters, it
+matches anything that has word syntax.)
address@hidden [:blank:]
+This matches space and tab only.
address@hidden [:cntrl:]
+This matches any @acronym{ASCII} control character.
address@hidden [:digit:]
+This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]}
+matches any digit, as well as @samp{+} and @samp{-}.
address@hidden [:graph:]
+This matches graphic characters---everything except @acronym{ASCII} control
+characters, space, and the delete character.
address@hidden [:lower:]
+This matches any lower-case letter, as determined by
+the current case table (@pxref{Case Tables}).
address@hidden [:multibyte:]
+This matches any multibyte character (@pxref{Text Representations}).
address@hidden [:nonascii:]
+This matches any address@hidden character.
address@hidden [:print:]
+This matches printing characters---everything except @acronym{ASCII} control
+characters and the delete character.
address@hidden [:punct:]
+This matches any punctuation character. (At present, for multibyte
+characters, it matches anything that has non-word syntax.)
address@hidden [:space:]
+This matches any character that has whitespace syntax
+(@pxref{Syntax Class Table}).
address@hidden [:unibyte:]
+This matches any unibyte character (@pxref{Text Representations}).
address@hidden [:upper:]
+This matches any upper-case letter, as determined by
+the current case table (@pxref{Case Tables}).
address@hidden [:word:]
+This matches any character that has word syntax (@pxref{Syntax Class
+Table}).
address@hidden [:xdigit:]
+This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a}
+through @samp{f} and @samp{A} through @samp{F}.
address@hidden table
+
address@hidden Regexp Backslash
address@hidden Backslash Constructs in Regular Expressions
+
+ For the most part, @samp{\} followed by any character matches only
+that character. However, there are several exceptions: certain
+two-character sequences starting with @samp{\} that have special
+meanings. (The character after the @samp{\} in such a sequence is
+always ordinary when used on its own.) Here is a table of the special
address@hidden constructs.
+
address@hidden @samp
address@hidden \|
address@hidden @samp{|} in regexp
address@hidden 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
address@hidden address@hidden
+
+Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar}
+but no other address@hidden
+
address@hidden|} applies to the largest possible surrounding expressions. Only
a
+surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of
address@hidden|address@hidden
+
+If you need full backtracking capability to handle multiple uses of
address@hidden|}, use the POSIX regular expression functions (@pxref{POSIX
+Regexps}).
+
address@hidden address@hidden@address@hidden
+is a postfix operator that repeats the previous pattern exactly @var{m}
+times. Thus, @address@hidden@}} matches the string @samp{xxxxx}
+and nothing else. @address@hidden@}r} matches string such as
address@hidden, @samp{cdddr}, @samp{cadar}, and so on.
+
address@hidden address@hidden@var{m},@address@hidden
+is a more general postfix operator that specifies repetition with a
+minimum of @var{m} repeats and a maximum of @var{n} repeats. If @var{m}
+is omitted, the minimum is 0; if @var{n} is omitted, there is no
+maximum.
+
+For example, @address@hidden,address@hidden matches the strings @samp{car},
address@hidden, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and
+nothing address@hidden
address@hidden@{0,address@hidden or @address@hidden,address@hidden is
equivalent to @samp{?}. @*
address@hidden@{0,address@hidden or @address@hidden,address@hidden is
equivalent to @samp{*}. @*
address@hidden@{1,address@hidden is equivalent to @samp{+}.
+
address@hidden \( @dots{} \)
address@hidden @samp{(} in regexp
address@hidden @samp{)} in regexp
address@hidden regexp grouping
+is a grouping construct that serves three purposes:
+
address@hidden
address@hidden
+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}.
+
address@hidden
+To enclose a complicated expression for the postfix operators @samp{*},
address@hidden and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches
address@hidden, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any
+number (zero or more) of @samp{na} strings.
+
address@hidden
+To record a matched substring for future reference with
address@hidden@var{digit}} (see below).
address@hidden enumerate
+
+This last application is not a consequence of the idea of a
+parenthetical grouping; it is a separate feature that was assigned as a
+second meaning to the same @samp{\( @dots{} \)} construct because, in
+practice, there was usually no conflict between the two meanings. But
+occasionally there is a conflict, and that led to the introduction of
+shy groups.
+
address@hidden \(?: @dots{} \)
+is the @dfn{shy group} construct. A shy group serves the first two
+purposes of an ordinary group (controlling the nesting of other
+operators), but it does not get a number, so you cannot refer back to
+its value with @address@hidden
+
+Shy groups are particularly useful for mechanically-constructed regular
+expressions because they can be added automatically without altering the
+numbering of any ordinary, non-shy groups.
+
address@hidden \(address@hidden: @dots{} \)
+is the @dfn{explicitly numbered group} construct. Normal groups get
+their number implicitly, based on their position, which can be
+inconvenient. This construct allows you to force a particular group
+number. There is no particular restriction on the numbering,
+e.g.@: you can have several groups with the same number in which case
+the last one to match (i.e.@: the rightmost match) will win.
+Implicitly numbered groups always get the smallest integer larger than
+the one of any previous group.
+
address@hidden address@hidden
+matches the same text that matched the @var{digit}th occurrence of a
+grouping (@samp{\( @dots{} \)}) construct.
+
+In other words, after the end of a group, the matcher remembers the
+beginning and end of the text matched by that group. 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 grouping constructs appearing in
+the entire regular expression passed to a search or matching function
+are assigned numbers 1 through 9 in the order that the open
+parentheses appear in the regular expression. So you can use
address@hidden through @samp{\9} to refer to the text matched by the
+corresponding grouping constructs.
+
+For example, @samp{\(.*\)\1} matches any newline-free string that is
+composed of two identical halves. The @samp{\(.*\)} matches the first
+half, which may be anything, but the @samp{\1} that follows must match
+the same exact text.
+
+If a @samp{\( @dots{} \)} construct matches more than once (which can
+happen, for instance, if it is followed by @samp{*}), only the last
+match is recorded.
+
+If a particular grouping construct in the regular expression was never
+matched---for instance, if it appears inside of an alternative that
+wasn't used, or inside of a repetition that repeated zero times---then
+the corresponding @address@hidden construct never matches
+anything. To use an artificial example,, @samp{\(foo\(b*\)\|lose\)\2}
+cannot match @samp{lose}: the second alternative inside the larger
+group matches it, but then @samp{\2} is undefined and can't match
+anything. But it can match @samp{foobb}, because the first
+alternative matches @samp{foob} and @samp{\2} matches @samp{b}.
+
address@hidden \w
address@hidden @samp{\w} in regexp
+matches any word-constituent character. The editor syntax table
+determines which characters these are. @xref{Syntax Tables}.
+
address@hidden \W
address@hidden @samp{\W} in regexp
+matches any character that is not a word constituent.
+
address@hidden address@hidden
address@hidden @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.
+
address@hidden address@hidden
address@hidden @samp{\S} in regexp
+matches any character whose syntax is not @var{code}.
+
address@hidden address@hidden
+matches any character whose category is @var{c}. Here @var{c} is a
+character that represents a category: thus, @samp{c} for Chinese
+characters or @samp{g} for Greek characters in the standard category
+table.
+
address@hidden address@hidden
+matches any character whose category is not @var{c}.
address@hidden 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. For all, the beginning and end of the accessible portion of
+the buffer are treated as if they were the actual beginning and end of
+the buffer.
+
address@hidden @samp
address@hidden \`
address@hidden @samp{\`} in regexp
+matches the empty string, but only at the beginning
+of the buffer or string being matched against.
+
address@hidden \'
address@hidden @samp{\'} in regexp
+matches the empty string, but only at the end of
+the buffer or string being matched against.
+
address@hidden \=
address@hidden @samp{\=} in regexp
+matches the empty string, but only at point.
+(This construct is not defined when matching against a string.)
+
address@hidden \b
address@hidden @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
address@hidden as a separate word. @samp{\bballs?\b} matches
address@hidden or @samp{balls} as a separate address@hidden
+
address@hidden matches at the beginning or end of the buffer (or string)
+regardless of what text appears next to it.
+
address@hidden \B
address@hidden @samp{\B} in regexp
+matches the empty string, but @emph{not} at the beginning or
+end of a word, nor at the beginning or end of the buffer (or string).
+
address@hidden \<
address@hidden @samp{\<} in regexp
+matches the empty string, but only at the beginning of a word.
address@hidden<} matches at the beginning of the buffer (or string) only if a
+word-constituent character follows.
+
address@hidden \>
address@hidden @samp{\>} in regexp
+matches the empty string, but only at the end of a word. @samp{\>}
+matches at the end of the buffer (or string) only if the contents end
+with a word-constituent character.
+
address@hidden \_<
address@hidden @samp{\_<} in regexp
+matches the empty string, but only at the beginning of a symbol. A
+symbol is a sequence of one or more word or symbol constituent
+characters. @samp{\_<} matches at the beginning of the buffer (or
+string) only if a symbol-constituent character follows.
+
address@hidden \_>
address@hidden @samp{\_>} in regexp
+matches the empty string, but only at the end of a symbol. @samp{\_>}
+matches at the end of the buffer (or string) only if the contents end
+with a symbol-constituent character.
address@hidden table
+
address@hidden invalid-regexp
+ Not every string is a valid regular expression. For example, a string
+that ends inside a character alternative without terminating @samp{]}
+is invalid, 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.
+
address@hidden Regexp Example
address@hidden node-name, next, previous, up
address@hidden Complex Regexp Example
+
+ Here is a complicated regexp which was formerly used by Emacs to
+recognize the end of a sentence together with any whitespace that
+follows. (Nowadays Emacs uses a similar but more complex default
+regexp constructed by the function @code{sentence-end}.
address@hidden Regexps}.)
+
+ 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.
+
address@hidden
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
address@hidden example
+
address@hidden
+In contrast, if you evaluate this string, you will see the following:
+
address@hidden
address@hidden
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
+ @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[
+]*"
address@hidden group
address@hidden example
+
address@hidden
+In this output, tab and newline appear as themselves.
+
+ This regular expression contains four parts in succession and can be
+deciphered as follows:
+
address@hidden @code
address@hidden [.?!]
+The first part of the pattern is a character alternative that matches
+any one of three characters: period, question mark, and exclamation
+mark. The match must begin with one of these three characters. (This
+is one point where the new default regexp used by Emacs differs from
+the old. The new value also allows some address@hidden
+characters that end a sentence without any following whitespace.)
+
address@hidden []\"')@}]*
+The second part of the pattern matches any closing braces and quotation
+marks, zero or more of them, that may follow the period, question mark
+or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in
+a string. The @samp{*} at the end indicates that the immediately
+preceding regular expression (a character alternative, in this case) may be
+repeated zero or more times.
+
address@hidden \\($\\|@ $\\|\t\\|@ @ \\)
+The third part of the pattern matches the whitespace that follows the
+end of a sentence: the end of a line (optionally with a space), or a
+tab, or two spaces. The double backslashes mark the parentheses and
+vertical bars as regular expression syntax; the parentheses delimit a
+group and the vertical bars separate alternatives. The dollar sign is
+used to match the end of a line.
+
address@hidden [ \t\n]*
+Finally, the last part of the pattern matches any additional whitespace
+beyond the minimum needed to end a sentence.
address@hidden table
+
address@hidden Regexp Functions
address@hidden Regular Expression Functions
+
+ These functions operate on regular expressions.
+
address@hidden regexp-quote string
+This function returns a regular expression whose only exact match is
address@hidden Using this regular expression in @code{looking-at} will
+succeed only if the next characters in the buffer are @var{string};
+using it in a search function will succeed if the text being searched
+contains @var{string}.
+
+This allows you to request an exact string match or search when calling
+a function that wants a regular expression.
+
address@hidden
address@hidden
+(regexp-quote "^The cat$")
+ @result{} "\\^The cat\\$"
address@hidden group
address@hidden 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:
+
address@hidden
address@hidden
+(re-search-forward
+ (concat "\\s-" (regexp-quote string) "\\s-"))
address@hidden group
address@hidden example
address@hidden defun
+
address@hidden regexp-opt strings &optional paren
+This function returns an efficient regular expression that will match
+any of the strings in the list @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 address@hidden, then the
+returned regular expression is always enclosed by at least one
+parentheses-grouping construct. If @var{paren} is @code{words}, then
+that construct is additionally surrounded by @samp{\<} and @samp{\>}.
+
+This simplified definition of @code{regexp-opt} produces a
+regular expression which is equivalent to the actual value
+(but not as efficient):
+
address@hidden
+(defun regexp-opt (strings paren)
+ (let ((open-paren (if paren "\\(" ""))
+ (close-paren (if paren "\\)" "")))
+ (concat open-paren
+ (mapconcat 'regexp-quote strings "\\|")
+ close-paren)))
address@hidden example
address@hidden defun
+
address@hidden regexp-opt-depth regexp
+This function returns the total number of grouping constructs
+(parenthesized expressions) in @var{regexp}. (This does not include
+shy groups.)
address@hidden defun
+
address@hidden Regexp Search
address@hidden Regular Expression Searching
address@hidden regular expression searching
address@hidden regexp searching
address@hidden 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}.
+
address@hidden 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
address@hidden, and leaves point at the end of the first match found.
+It returns the new value of point.
+
+If @var{limit} is address@hidden, it must be a position in the current
+buffer. It specifies 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; the search
+is repeated that many times; each repetition starts at the end of the
+previous match. If all these successive searches succeed, the search
+succeeds, moving point and returning its new value. Otherwise the
+search fails. What @code{re-search-forward} does when the search
+fails depends on the value of @var{noerror}:
+
address@hidden @asis
address@hidden @code{nil}
+Signal a @code{search-failed} error.
address@hidden @code{t}
+Do nothing and return @code{nil}.
address@hidden anything else
+Move point to @var{limit} (or the end of the accessible portion of the
+buffer) and return @code{nil}.
address@hidden table
+
+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).
+
address@hidden
address@hidden
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
address@hidden group
+
address@hidden
+(re-search-forward "[a-z]+" nil t 5)
+ @result{} 27
+
+---------- Buffer: foo ----------
+I read "The cat in the address@hidden
+comes back" twice.
+---------- Buffer: foo ----------
address@hidden group
address@hidden example
address@hidden deffn
+
address@hidden 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
address@hidden 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 (and yet ends before the
+starting point). The reason for this 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.
address@hidden deffn
+
address@hidden 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 address@hidden, the search starts
+at that index in @var{string}.
+
+For example,
+
address@hidden
address@hidden
+(string-match
+ "quick" "The quick brown fox jumped quickly.")
+ @result{} 4
address@hidden group
address@hidden
+(string-match
+ "quick" "The quick brown fox jumped quickly." 8)
+ @result{} 27
address@hidden group
address@hidden example
+
address@hidden
+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}.
+
address@hidden
address@hidden
+(string-match
+ "quick" "The quick brown fox jumped quickly." 8)
+ @result{} 27
address@hidden group
+
address@hidden
+(match-end 0)
+ @result{} 32
address@hidden group
address@hidden example
address@hidden defun
+
address@hidden 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}.
address@hidden Data}.
+
+In this example, point is located directly before the @samp{T}. If it
+were anywhere else, the result would be @code{nil}.
+
address@hidden
address@hidden
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
+
+(looking-at "The cat in the hat$")
+ @result{} t
address@hidden group
address@hidden example
address@hidden defun
+
address@hidden looking-back regexp &optional limit
+This function returns @code{t} if @var{regexp} matches text before
+point, ending at point, and @code{nil} otherwise.
+
+Because regular expression matching works only going forward, this is
+implemented by searching backwards from point for a match that ends at
+point. That can be quite slow if it has to search a long distance.
+You can bound the time required by specifying @var{limit}, which says
+not to search before @var{limit}. In this case, the match that is
+found must begin at or after @var{limit}.
+
address@hidden
address@hidden
+---------- Buffer: foo ----------
+I read "@point{}The cat in the hat
+comes back" twice.
+---------- Buffer: foo ----------
+
+(looking-back "read \"" 3)
+ @result{} t
+(looking-back "read \"" 4)
+ @result{} nil
address@hidden group
address@hidden example
address@hidden defun
+
address@hidden search-spaces-regexp
+If this variable is address@hidden, it should be a regular expression
+that says how to search for whitespace. In that case, any group of
+spaces in a regular expression being searched for stands for use of
+this regular expression. However, spaces inside of constructs such as
address@hidden@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by
address@hidden
+
+Since this variable affects all regular expression search and match
+constructs, you should bind it temporarily for as small as possible
+a part of the code.
address@hidden defvar
+
address@hidden POSIX Regexps
address@hidden 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.
+
+ The POSIX search and match functions do not properly support the
+non-greedy repetition operators. This is because POSIX backtracking
+conflicts with the semantics of non-greedy repetition.
+
address@hidden 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.
address@hidden defun
+
address@hidden 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.
address@hidden defun
+
address@hidden 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.
address@hidden defun
+
address@hidden 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.
address@hidden defun
+
address@hidden Match Data
address@hidden The Match Data
address@hidden match data
+
+ Emacs keeps track of the start and end positions of the segments of
+text found during a search; this is called the @dfn{match data}.
+Thanks to the match data, you can search for a complex pattern, such
+as a date in a mail 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.
+
address@hidden
+* 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.
address@hidden menu
+
address@hidden Replacing Match
address@hidden Replacing the Text that Matched
address@hidden replace matched text
+
+ This function replaces all or part of the text matched by the last
+search. It works by means of the match data.
+
address@hidden case in replacements
address@hidden 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
address@hidden
+
+If you did the last search in a buffer, you should specify @code{nil}
+for @var{string} and make sure that the current buffer when you call
address@hidden is the one in which you did the searching or
+matching. 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 address@hidden, then @code{replace-match} uses
+the replacement text without case conversion; otherwise, it converts
+the replacement text depending upon the capitalization of the text to
+be replaced. If the original text is all upper case, this converts
+the replacement text to upper case. If all words of the original text
+are capitalized, this capitalizes all the words of the replacement
+text. If all the words are one-letter and they are all upper case,
+they are treated as capitalized words rather than all-upper-case
+words.
+
+If @var{literal} is address@hidden, 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:
+
address@hidden @asis
address@hidden @samp{\&}
address@hidden @samp{&} in replacement
address@hidden&} stands for the entire text being replaced.
+
address@hidden @address@hidden
address@hidden @address@hidden in replacement
address@hidden@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{\(@dots{}\)}.
+If the @var{n}th subexpression never matched, an empty string is substituted.
+
address@hidden @samp{\\}
address@hidden @samp{\} in replacement
address@hidden stands for a single @samp{\} in the replacement text.
address@hidden table
+
+These substitutions occur after case conversion, if any,
+so the strings they substitute are never case-converted.
+
+If @var{subexp} is address@hidden, 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{\(ba*r\)}.
address@hidden defun
+
address@hidden Simple Match Data
address@hidden 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, if it succeeded.
+
+ 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
address@hidden subexpression is found by counting occurrences of
address@hidden(} 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.
+
+ Every successful search sets the match data. Therefore, you should
+query the match data immediately after searching, before calling any
+other function that might perform another search. Alternatively, you
+may save and restore the match data (@pxref{Saving Match Data}) around
+the call to functions that could perform another search.
+
+ 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. So don't try to rely on the value of the match data after
+a failing search.
+
address@hidden 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 the last such operation was done against a string with
address@hidden, 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
address@hidden is the one in which you did the searching or
+matching.
+
+The value is @code{nil} if @var{count} is out of range, or for a
+subexpression inside a @samp{\|} alternative that wasn't used or a
+repetition that repeated zero times.
address@hidden defun
+
address@hidden match-string-no-properties count &optional in-string
+This function is like @code{match-string} except that the result
+has no text properties.
address@hidden defun
+
address@hidden 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 or a repetition that repeated zero times.
address@hidden defun
+
address@hidden 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.
address@hidden defun
+
+ Here is an example of using the match data, with a comment showing the
+positions within the text:
+
address@hidden
address@hidden
+(string-match "\\(qu\\)\\(ick\\)"
+ "The quick fox jumped quickly.")
+ ;0123456789
+ @result{} 4
address@hidden group
+
address@hidden
+(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"
address@hidden group
+
address@hidden
+(match-beginning 1) ; @r{The beginning of the match}
+ @result{} 4 ; @r{with @samp{qu} is at index 4.}
address@hidden group
+
address@hidden
+(match-beginning 2) ; @r{The beginning of the match}
+ @result{} 6 ; @r{with @samp{ick} is at index 6.}
address@hidden group
+
address@hidden
+(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.}
address@hidden group
address@hidden 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
address@hidden 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}).
+
address@hidden
address@hidden
+(list
+ (re-search-forward "The \\(cat \\)")
+ (match-beginning 0)
+ (match-beginning 1))
+ @result{} (9 9 13)
address@hidden group
+
address@hidden
+---------- Buffer: foo ----------
+I read "The cat @point{}in the hat comes back" twice.
+ ^ ^
+ 9 13
+---------- Buffer: foo ----------
address@hidden group
address@hidden example
+
address@hidden
+(In this case, the index returned is a buffer position; the first
+character of the buffer counts as 1.)
+
address@hidden Entire Match Data
address@hidden 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.
+
address@hidden match-data &optional integers reuse reseat
+This function returns a list of positions (markers or integers) that
+record 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
address@hidden
+number address@hidden
address@hidden ifnottex
address@hidden
+number {\mathsurround=0pt $2n$}
address@hidden tex
+corresponds to @code{(match-beginning @var{n})}; and
+element
address@hidden
+number address@hidden + 1
address@hidden ifnottex
address@hidden
+number {\mathsurround=0pt $2n+1$}
address@hidden tex
+corresponds to @code{(match-end @var{n})}.
+
+Normally all the elements are markers or @code{nil}, but if
address@hidden is address@hidden, that means to use integers instead
+of markers. (In that case, the buffer itself is appended as an
+additional element at the end of the list, to facilitate complete
+restoration of the match data.) If the last match was done on a
+string with @code{string-match}, then integers are always used,
+since markers can't point into a string.
+
+If @var{reuse} is address@hidden, it should be a list. In that case,
address@hidden stores the match data in @var{reuse}. That is,
address@hidden is destructively modified. @var{reuse} does not need to
+have the right length. If it is not long enough to contain the match
+data, it is extended. If it is too long, the length of @var{reuse}
+stays the same, but the elements that were not used are set to
address@hidden The purpose of this feature is to reduce the need for
+garbage collection.
+
+If @var{reseat} is address@hidden, all markers on the @var{reuse} list
+are reseated to point to nowhere.
+
+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.
+
address@hidden
address@hidden
+(match-data)
+ @result{} (#<marker at 9 in foo>
+ #<marker at 17 in foo>
+ #<marker at 13 in foo>
+ #<marker at 17 in foo>)
address@hidden group
address@hidden example
address@hidden defun
+
address@hidden set-match-data match-list &optional reseat
+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
address@hidden (More precisely, anything that has the same format
+will work.)
+
+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.
+
+If @var{reseat} is address@hidden, all markers on the @var{match-list} list
+are reseated to point to nowhere.
+
address@hidden store-match-data
address@hidden is a semi-obsolete alias for @code{set-match-data}.
address@hidden defun
+
address@hidden Saving Match Data
address@hidden 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:
+
address@hidden
address@hidden
+(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!}
address@hidden group
address@hidden example
+
+ You can save and restore the match data with @code{save-match-data}:
+
address@hidden save-match-data address@hidden
+This macro executes @var{body}, saving and restoring the match
+data around it. The return value is the value of the last form in
address@hidden
address@hidden 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:
+
address@hidden
address@hidden
+(let ((data (match-data)))
+ (unwind-protect
+ @dots{} ; @r{Ok to change the original match data.}
+ (set-match-data data)))
address@hidden group
address@hidden example
+
+ Emacs automatically saves and restores the match data when it runs
+process filter functions (@pxref{Filter Functions}) and process
+sentinels (@pxref{Sentinels}).
+
address@hidden
+ Here is a function which restores the match data provided the buffer
+associated with it still exists.
+
address@hidden
address@hidden
+(defun restore-match-data (data)
address@hidden It is incorrect to split the first line of a doc string.
address@hidden 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))
address@hidden group
+ (while d
+ (and (car d)
+ (null (marker-buffer (car d)))
address@hidden
+ ;; @file{match-data} @r{buffer is deleted.}
+ (throw 'foo nil))
+ (setq d (cdr d)))
+ (set-match-data data))))
address@hidden group
address@hidden smallexample
address@hidden ignore
+
address@hidden Search and Replace
address@hidden Search and Replace
address@hidden replacement after search
address@hidden searching and replacing
+
+ If you want to find all matches for a regexp in part of the buffer,
+and replace them, the best way is to write an explicit loop using
address@hidden and @code{replace-match}, like this:
+
address@hidden
+(while (re-search-forward "foo[ \t]+bar" nil t)
+ (replace-match "foobar"))
address@hidden example
+
address@hidden
address@hidden Match,, Replacing the Text that Matched}, for a
+description of @code{replace-match}.
+
+ However, replacing matches in a string is more complex, especially
+if you want to do it efficiently. So Emacs provides a function to do
+this.
+
address@hidden replace-regexp-in-string regexp rep string &optional fixedcase
literal subexp start
+This function copies @var{string} and searches it for matches for
address@hidden, and replaces them with @var{rep}. It returns the
+modified copy. If @var{start} is address@hidden, the search for
+matches starts at that index in @var{string}, so matches starting
+before that index are not changed.
+
+This function uses @code{replace-match} to do the replacement, and it
+passes the optional arguments @var{fixedcase}, @var{literal} and
address@hidden along to @code{replace-match}.
+
+Instead of a string, @var{rep} can be a function. In that case,
address@hidden calls @var{rep} for each match,
+passing the text of the match as its sole argument. It collects the
+value @var{rep} returns and passes that to @code{replace-match} as the
+replacement string. The match-data at this point are the result
+of matching @var{regexp} against a substring of @var{string}.
address@hidden defun
+
+ If you want to write a command along the lines of @code{query-replace},
+you can use @code{perform-replace} to do the work.
+
address@hidden perform-replace from-string replacements query-flag regexp-flag
delimited-flag &optional repeat-count map start end
+This function is the guts of @code{query-replace} and related
+commands. It searches for occurrences of @var{from-string} in the
+text between positions @var{start} and @var{end} and replaces some or
+all of them. If @var{start} is @code{nil} (or omitted), point is used
+instead, and the end of the buffer's accessible portion is used for
address@hidden
+
+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 address@hidden, then @var{from-string} is
+considered a regular expression; otherwise, it must match literally. If
address@hidden is address@hidden, 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{replacements} is a cons cell, @code{(@var{function}
+. @var{data})}, this means to call @var{function} after each match to
+get the replacement text. This function is called with two arguments:
address@hidden, and the number of replacements already made.
+
+If @var{repeat-count} is address@hidden, it should be an integer. Then
+it specifies how many times to use each of the strings in the
address@hidden list before advancing cyclically to the next one.
+
+If @var{from-string} contains upper-case letters, then
address@hidden binds @code{case-fold-search} to @code{nil}, and
+it uses the @code{replacements} without altering the case of them.
+
+Normally, the keymap @code{query-replace-map} defines the possible
+user responses for queries. The argument @var{map}, if
address@hidden, specifies a keymap to use instead of
address@hidden
address@hidden defun
+
address@hidden query-replace-map
+This variable holds a special keymap that defines the valid user
+responses for @code{perform-replace} and the commands that use it, as
+well as @code{y-or-n-p} and @code{map-y-or-n-p}. This map is unusual
+in two ways:
+
address@hidden @bullet
address@hidden
+The ``key bindings'' are not commands, just symbols that are meaningful
+to the functions that use this map.
+
address@hidden
+Prefix keys are not supported; each key binding must be for a
+single-event key sequence. This is because the functions don't use
address@hidden to get the input; instead, they read a single
+event and look it up ``by hand.''
address@hidden itemize
address@hidden defvar
+
+Here are the meaningful ``bindings'' for @code{query-replace-map}.
+Several of them are meaningful only for @code{query-replace} and
+friends.
+
address@hidden @code
address@hidden act
+Do take the action being considered---in other words, ``yes.''
+
address@hidden skip
+Do not take action for this question---in other words, ``no.''
+
address@hidden exit
+Answer this question ``no,'' and give up on the entire series of
+questions, assuming that the answers will be ``no.''
+
address@hidden act-and-exit
+Answer this question ``yes,'' and give up on the entire series of
+questions, assuming that subsequent answers will be ``no.''
+
address@hidden act-and-show
+Answer this question ``yes,'' but show the results---don't advance yet
+to the next question.
+
address@hidden automatic
+Answer this question and all subsequent questions in the series with
+``yes,'' without further user interaction.
+
address@hidden backup
+Move back to the previous place that a question was asked about.
+
address@hidden edit
+Enter a recursive edit to deal with this question---instead of any
+other action that would normally be taken.
+
address@hidden delete-and-edit
+Delete the text being considered, then enter a recursive edit to replace
+it.
+
address@hidden recenter
+Redisplay and center the window, then ask the same question again.
+
address@hidden quit
+Perform a quit right away. Only @code{y-or-n-p} and related functions
+use this answer.
+
address@hidden help
+Display some help, then ask again.
address@hidden table
+
address@hidden Standard Regexps
address@hidden Standard Regular Expressions Used in Editing
address@hidden regexps used standardly in editing
address@hidden standard regexps used in editing
+
+ This section describes some variables that hold regular expressions
+used for certain purposes in editing:
+
address@hidden page-delimiter
+This is the regular expression describing line-beginnings that separate
+pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or
address@hidden"^\C-l"}); this matches a line that starts with a formfeed
+character.
address@hidden defvar
+
+ The following two regular expressions should @emph{not} assume the
+match always starts at the beginning of a line; they should not use
address@hidden to anchor the match. Most often, the paragraph commands do
+check for a match only at the beginning of a line, which means that
address@hidden would be superfluous. When there is a nonzero left margin,
+they accept matches that start after the left margin. In that case, a
address@hidden would be incorrect. However, a @samp{^} is harmless in modes
+where a left margin is never used.
+
address@hidden 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
address@hidden@code{"[@ \t\f]*$"}}, which matches a line that consists entirely
of
+spaces, tabs, and form feeds (after its left margin).
address@hidden defvar
+
address@hidden paragraph-start
+This is the regular expression for recognizing the beginning of a line
+that starts @emph{or} separates paragraphs. The default value is
address@hidden@code{"\f\\|[ \t]*$"}}, which matches a line containing only
+whitespace or starting with a form feed (after its left margin).
address@hidden defvar
+
address@hidden sentence-end
+If address@hidden, the value should be a regular expression describing
+the end of a sentence, including the whitespace following the
+sentence. (All paragraph boundaries also end sentences, regardless.)
+
+If the value is @code{nil}, the default, then the function
address@hidden has to construct the regexp. That is why you
+should always call the function @code{sentence-end} to obtain the
+regexp to be used to recognize the end of a sentence.
address@hidden defvar
+
address@hidden sentence-end
+This function returns the value of the variable @code{sentence-end},
+if address@hidden Otherwise it returns a default value based on the
+values of the variables @code{sentence-end-double-space}
+(@pxref{Definition of sentence-end-double-space}),
address@hidden and
address@hidden
address@hidden defun
+
address@hidden
+ arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f
address@hidden ignore