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1627 lines
61 KiB
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1627 lines
61 KiB
Plaintext
@c -*-texinfo-*-
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@c This is part of the GNU Emacs Lisp Reference Manual.
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@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
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@c Free Software Foundation, Inc.
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@c See the file elisp.texi for copying conditions.
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@setfilename ../info/searching
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@node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top
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@chapter Searching and Matching
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@cindex searching
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GNU Emacs provides two ways to search through a buffer for specified
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text: exact string searches and regular expression searches. After a
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regular expression search, you can examine the @dfn{match data} to
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determine which text matched the whole regular expression or various
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portions of it.
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@menu
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* String Search:: Search for an exact match.
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* Regular Expressions:: Describing classes of strings.
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* Regexp Search:: Searching for a match for a regexp.
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* POSIX Regexps:: Searching POSIX-style for the longest match.
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* Search and Replace:: Internals of @code{query-replace}.
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* Match Data:: Finding out which part of the text matched
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various parts of a regexp, after regexp search.
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* Searching and Case:: Case-independent or case-significant searching.
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* Standard Regexps:: Useful regexps for finding sentences, pages,...
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@end menu
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The @samp{skip-chars@dots{}} functions also perform a kind of searching.
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@xref{Skipping Characters}.
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@node String Search
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@section Searching for Strings
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@cindex string search
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These are the primitive functions for searching through the text in a
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buffer. They are meant for use in programs, but you may call them
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interactively. If you do so, they prompt for the search string; the
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arguments @var{limit} and @var{noerror} are @code{nil}, and @var{repeat}
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is 1.
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These search functions convert the search string to multibyte if the
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buffer is multibyte; they convert the search string to unibyte if the
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buffer is unibyte. @xref{Text Representations}.
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@deffn Command search-forward string &optional limit noerror repeat
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This function searches forward from point for an exact match for
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@var{string}. If successful, it sets point to the end of the occurrence
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found, and returns the new value of point. If no match is found, the
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value and side effects depend on @var{noerror} (see below).
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@c Emacs 19 feature
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In the following example, point is initially at the beginning of the
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line. Then @code{(search-forward "fox")} moves point after the last
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letter of @samp{fox}:
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@example
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@group
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---------- Buffer: foo ----------
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@point{}The quick brown fox jumped over the lazy dog.
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---------- Buffer: foo ----------
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@end group
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@group
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(search-forward "fox")
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@result{} 20
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---------- Buffer: foo ----------
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The quick brown fox@point{} jumped over the lazy dog.
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---------- Buffer: foo ----------
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@end group
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@end example
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The argument @var{limit} specifies the upper bound to the search. (It
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must be a position in the current buffer.) No match extending after
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that position is accepted. If @var{limit} is omitted or @code{nil}, it
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defaults to the end of the accessible portion of the buffer.
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@kindex search-failed
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What happens when the search fails depends on the value of
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@var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed}
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error is signaled. If @var{noerror} is @code{t}, @code{search-forward}
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returns @code{nil} and does nothing. If @var{noerror} is neither
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@code{nil} nor @code{t}, then @code{search-forward} moves point to the
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upper bound and returns @code{nil}. (It would be more consistent now to
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return the new position of point in that case, but some existing
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programs may depend on a value of @code{nil}.)
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If @var{repeat} is supplied (it must be a positive number), then the
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search is repeated that many times (each time starting at the end of the
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previous time's match). If these successive searches succeed, the
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function succeeds, moving point and returning its new value. Otherwise
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the search fails, leaving point where it started.
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@end deffn
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@deffn Command search-backward string &optional limit noerror repeat
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This function searches backward from point for @var{string}. It is
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just like @code{search-forward} except that it searches backwards and
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leaves point at the beginning of the match.
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@end deffn
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@deffn Command word-search-forward string &optional limit noerror repeat
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@cindex word search
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This function searches forward from point for a ``word'' match for
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@var{string}. If it finds a match, it sets point to the end of the
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match found, and returns the new value of point.
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@c Emacs 19 feature
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Word matching regards @var{string} as a sequence of words, disregarding
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punctuation that separates them. It searches the buffer for the same
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sequence of words. Each word must be distinct in the buffer (searching
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for the word @samp{ball} does not match the word @samp{balls}), but the
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details of punctuation and spacing are ignored (searching for @samp{ball
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boy} does match @samp{ball. Boy!}).
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In this example, point is initially at the beginning of the buffer; the
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search leaves it between the @samp{y} and the @samp{!}.
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@example
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@group
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---------- Buffer: foo ----------
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@point{}He said "Please! Find
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the ball boy!"
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---------- Buffer: foo ----------
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@end group
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@group
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(word-search-forward "Please find the ball, boy.")
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@result{} 35
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---------- Buffer: foo ----------
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He said "Please! Find
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the ball boy@point{}!"
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---------- Buffer: foo ----------
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@end group
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@end example
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If @var{limit} is non-@code{nil} (it must be a position in the current
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buffer), then it is the upper bound to the search. The match found must
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not extend after that position.
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If @var{noerror} is @code{nil}, then @code{word-search-forward} signals
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an error if the search fails. If @var{noerror} is @code{t}, then it
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returns @code{nil} instead of signaling an error. If @var{noerror} is
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neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the
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end of the buffer) and returns @code{nil}.
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If @var{repeat} is non-@code{nil}, then the search is repeated that many
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times. Point is positioned at the end of the last match.
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@end deffn
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@deffn Command word-search-backward string &optional limit noerror repeat
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This function searches backward from point for a word match to
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@var{string}. This function is just like @code{word-search-forward}
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except that it searches backward and normally leaves point at the
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beginning of the match.
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@end deffn
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@node Regular Expressions
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@section Regular Expressions
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@cindex regular expression
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@cindex regexp
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A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that
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denotes a (possibly infinite) set of strings. Searching for matches for
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a regexp is a very powerful operation. This section explains how to write
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regexps; the following section says how to search for them.
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@menu
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* Syntax of Regexps:: Rules for writing regular expressions.
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* Regexp Functions:: Functions for operating on regular expressions.
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* Regexp Example:: Illustrates regular expression syntax.
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@end menu
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@node Syntax of Regexps
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@subsection Syntax of Regular Expressions
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Regular expressions have a syntax in which a few characters are
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special constructs and the rest are @dfn{ordinary}. An ordinary
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character is a simple regular expression that matches that character and
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nothing else. The special characters are @samp{.}, @samp{*}, @samp{+},
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@samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new
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special characters will be defined in the future. Any other character
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appearing in a regular expression is ordinary, unless a @samp{\}
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precedes it.
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For example, @samp{f} is not a special character, so it is ordinary, and
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therefore @samp{f} is a regular expression that matches the string
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@samp{f} and no other string. (It does @emph{not} match the string
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@samp{fg}, but it does match a @emph{part} of that string.) Likewise,
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@samp{o} is a regular expression that matches only @samp{o}.@refill
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Any two regular expressions @var{a} and @var{b} can be concatenated. The
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result is a regular expression that matches a string if @var{a} matches
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some amount of the beginning of that string and @var{b} matches the rest of
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the string.@refill
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As a simple example, we can concatenate the regular expressions @samp{f}
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and @samp{o} to get the regular expression @samp{fo}, which matches only
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the string @samp{fo}. Still trivial. To do something more powerful, you
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need to use one of the special regular expression constructs.
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@menu
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* Regexp Special:: Special characters in regular expressions.
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* Char Classes:: Character classes used in regular expressions.
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* Regexp Backslash:: Backslash-sequences in regular expressions.
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@end menu
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@node Regexp Special
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@subsubsection Special Characters in Regular Expressions
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Here is a list of the characters that are special in a regular
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expression.
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@need 800
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@table @asis
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@item @samp{.}@: @r{(Period)}
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@cindex @samp{.} in regexp
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is a special character that matches any single character except a newline.
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Using concatenation, we can make regular expressions like @samp{a.b}, which
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matches any three-character string that begins with @samp{a} and ends with
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@samp{b}.@refill
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@item @samp{*}
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@cindex @samp{*} in regexp
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is not a construct by itself; it is a postfix operator that means to
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match the preceding regular expression repetitively as many times as
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possible. Thus, @samp{o*} matches any number of @samp{o}s (including no
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@samp{o}s).
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@samp{*} always applies to the @emph{smallest} possible preceding
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expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating
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@samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on.
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The matcher processes a @samp{*} construct by matching, immediately, as
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many repetitions as can be found. Then it continues with the rest of
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the pattern. If that fails, backtracking occurs, discarding some of the
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matches of the @samp{*}-modified construct in the hope that that will
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make it possible to match the rest of the pattern. For example, in
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matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*}
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first tries to match all three @samp{a}s; but the rest of the pattern is
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@samp{ar} and there is only @samp{r} left to match, so this try fails.
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The next alternative is for @samp{a*} to match only two @samp{a}s. With
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this choice, the rest of the regexp matches successfully.@refill
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Nested repetition operators can be extremely slow if they specify
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backtracking loops. For example, it could take hours for the regular
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expression @samp{\(x+y*\)*a} to try to match the sequence
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@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately fails.
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The slowness is because Emacs must try each imaginable way of grouping
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the 35 @samp{x}s before concluding that none of them can work. To make
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sure your regular expressions run fast, check nested repetitions
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carefully.
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@item @samp{+}
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@cindex @samp{+} in regexp
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is a postfix operator, similar to @samp{*} except that it must match
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the preceding expression at least once. So, for example, @samp{ca+r}
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matches the strings @samp{car} and @samp{caaaar} but not the string
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@samp{cr}, whereas @samp{ca*r} matches all three strings.
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@item @samp{?}
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@cindex @samp{?} in regexp
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is a postfix operator, similar to @samp{*} except that it must match the
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preceding expression either once or not at all. For example,
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@samp{ca?r} matches @samp{car} or @samp{cr}; nothing else.
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@item @samp{*?}, @samp{+?}, @samp{??}
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These are ``non-greedy'' variants of the operators @samp{*}, @samp{+}
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and @samp{?}. Where those operators match the largest possible
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substring (consistent with matching the entire containing expression),
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the non-greedy variants match the smallest possible substring
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(consistent with matching the entire containing expression).
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For example, the regular expression @samp{c[ad]*a} when applied to the
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string @samp{cdaaada} matches the whole string; but the regular
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expression @samp{c[ad]*?a}, applied to that same string, matches just
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@samp{cda}. (The smallest possible match here for @samp{[ad]*?} that
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permits the whole expression to match is @samp{d}.)
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@item @samp{[ @dots{} ]}
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@cindex character alternative (in regexp)
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@cindex @samp{[} in regexp
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@cindex @samp{]} in regexp
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is a @dfn{character alternative}, which begins with @samp{[} and is
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terminated by @samp{]}. In the simplest case, the characters between
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the two brackets are what this character alternative can match.
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Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and
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@samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s
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(including the empty string), from which it follows that @samp{c[ad]*r}
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matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc.
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You can also include character ranges in a character alternative, by
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writing the starting and ending characters with a @samp{-} between them.
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Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter. Ranges may be
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intermixed freely with individual characters, as in @samp{[a-z$%.]},
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which matches any lower case @acronym{ASCII} letter or @samp{$}, @samp{%} or
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period.
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Note that the usual regexp special characters are not special inside a
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character alternative. A completely different set of characters is
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special inside character alternatives: @samp{]}, @samp{-} and @samp{^}.
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To include a @samp{]} in a character alternative, you must make it the
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first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}.
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To include a @samp{-}, write @samp{-} as the first or last character of
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the character alternative, or put it after a range. Thus, @samp{[]-]}
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matches both @samp{]} and @samp{-}.
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To include @samp{^} in a character alternative, put it anywhere but at
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the beginning.
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The beginning and end of a range of multibyte characters must be in
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the same character set (@pxref{Character Sets}). Thus,
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@code{"[\x8e0-\x97c]"} is invalid because character 0x8e0 (@samp{a}
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with grave accent) is in the Emacs character set for Latin-1 but the
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character 0x97c (@samp{u} with diaeresis) is in the Emacs character
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set for Latin-2. (We use Lisp string syntax to write that example,
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and a few others in the next few paragraphs, in order to include hex
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escape sequences in them.)
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If a range starts with a unibyte character @var{c} and ends with a
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multibyte character @var{c2}, the range is divided into two parts: one
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is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where
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@var{c1} is the first character of the charset to which @var{c2}
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belongs.
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You cannot always match all non-@acronym{ASCII} characters with the regular
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expression @code{"[\200-\377]"}. This works when searching a unibyte
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buffer or string (@pxref{Text Representations}), but not in a multibyte
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buffer or string, because many non-@acronym{ASCII} characters have codes
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above octal 0377. However, the regular expression @code{"[^\000-\177]"}
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does match all non-@acronym{ASCII} characters (see below regarding @samp{^}),
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in both multibyte and unibyte representations, because only the
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@acronym{ASCII} characters are excluded.
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Starting in Emacs 21, a character alternative can also specify named
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character classes (@pxref{Char Classes}). This is a POSIX feature whose
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syntax is @samp{[:@var{class}:]}. Using a character class is equivalent
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to mentioning each of the characters in that class; but the latter is
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not feasible in practice, since some classes include thousands of
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different characters.
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@item @samp{[^ @dots{} ]}
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@cindex @samp{^} in regexp
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@samp{[^} begins a @dfn{complemented character alternative}, which matches any
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character except the ones specified. Thus, @samp{[^a-z0-9A-Z]} matches
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all characters @emph{except} letters and digits.
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@samp{^} is not special in a character alternative unless it is the first
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character. The character following the @samp{^} is treated as if it
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were first (in other words, @samp{-} and @samp{]} are not special there).
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A complemented character alternative can match a newline, unless newline is
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mentioned as one of the characters not to match. This is in contrast to
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the handling of regexps in programs such as @code{grep}.
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@item @samp{^}
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@cindex beginning of line in regexp
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is a special character that matches the empty string, but only at the
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beginning of a line in the text being matched. Otherwise it fails to
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match anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at
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the beginning of a line.
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When matching a string instead of a buffer, @samp{^} matches at the
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beginning of the string or after a newline character.
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For historical compatibility reasons, @samp{^} can be used only at the
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beginning of the regular expression, or after @samp{\(} or @samp{\|}.
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@item @samp{$}
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@cindex @samp{$} in regexp
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@cindex end of line in regexp
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is similar to @samp{^} but matches only at the end of a line. Thus,
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@samp{x+$} matches a string of one @samp{x} or more at the end of a line.
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When matching a string instead of a buffer, @samp{$} matches at the end
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of the string or before a newline character.
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For historical compatibility reasons, @samp{$} can be used only at the
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end of the regular expression, or before @samp{\)} or @samp{\|}.
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@item @samp{\}
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@cindex @samp{\} in regexp
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has two functions: it quotes the special characters (including
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@samp{\}), and it introduces additional special constructs.
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Because @samp{\} quotes special characters, @samp{\$} is a regular
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expression that matches only @samp{$}, and @samp{\[} is a regular
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expression that matches only @samp{[}, and so on.
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Note that @samp{\} also has special meaning in the read syntax of Lisp
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strings (@pxref{String Type}), and must be quoted with @samp{\}. For
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example, the regular expression that matches the @samp{\} character is
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@samp{\\}. To write a Lisp string that contains the characters
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@samp{\\}, Lisp syntax requires you to quote each @samp{\} with another
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@samp{\}. Therefore, the read syntax for a regular expression matching
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@samp{\} is @code{"\\\\"}.@refill
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@end table
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@strong{Please note:} For historical compatibility, special characters
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are treated as ordinary ones if they are in contexts where their special
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meanings make no sense. For example, @samp{*foo} treats @samp{*} as
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ordinary since there is no preceding expression on which the @samp{*}
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can act. It is poor practice to depend on this behavior; quote the
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special character anyway, regardless of where it appears.@refill
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@node Char Classes
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@subsubsection Character Classes
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@cindex character classes in regexp
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Here is a table of the classes you can use in a character alternative,
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in Emacs 21, and what they mean:
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@table @samp
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@item [:ascii:]
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This matches any @acronym{ASCII} (unibyte) character.
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@item [:alnum:]
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This matches any letter or digit. (At present, for multibyte
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characters, it matches anything that has word syntax.)
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@item [:alpha:]
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This matches any letter. (At present, for multibyte characters, it
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matches anything that has word syntax.)
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@item [:blank:]
|
|
This matches space and tab only.
|
|
@item [:cntrl:]
|
|
This matches any @acronym{ASCII} control character.
|
|
@item [:digit:]
|
|
This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]}
|
|
matches any digit, as well as @samp{+} and @samp{-}.
|
|
@item [:graph:]
|
|
This matches graphic characters---everything except @acronym{ASCII} control
|
|
characters, space, and the delete character.
|
|
@item [:lower:]
|
|
This matches any lower-case letter, as determined by
|
|
the current case table (@pxref{Case Tables}).
|
|
@item [:nonascii:]
|
|
This matches any non-@acronym{ASCII} (multibyte) character.
|
|
@item [:print:]
|
|
This matches printing characters---everything except @acronym{ASCII} control
|
|
characters and the delete character.
|
|
@item [:punct:]
|
|
This matches any punctuation character. (At present, for multibyte
|
|
characters, it matches anything that has non-word syntax.)
|
|
@item [:space:]
|
|
This matches any character that has whitespace syntax
|
|
(@pxref{Syntax Class Table}).
|
|
@item [:upper:]
|
|
This matches any upper-case letter, as determined by
|
|
the current case table (@pxref{Case Tables}).
|
|
@item [:word:]
|
|
This matches any character that has word syntax (@pxref{Syntax Class
|
|
Table}).
|
|
@item [:xdigit:]
|
|
This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a}
|
|
through @samp{f} and @samp{A} through @samp{F}.
|
|
@end table
|
|
|
|
@node Regexp Backslash
|
|
@subsubsection 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
|
|
@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
|
|
|
|
If you need full backtracking capability to handle multiple uses of
|
|
@samp{\|}, use the POSIX regular expression functions (@pxref{POSIX
|
|
Regexps}).
|
|
|
|
@item \@{@var{m}\@}
|
|
is a postfix operator that repeats the previous pattern exactly @var{m}
|
|
times. Thus, @samp{x\@{5\@}} matches the string @samp{xxxxx}
|
|
and nothing else. @samp{c[ad]\@{3\@}r} matches string such as
|
|
@samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on.
|
|
|
|
@item \@{@var{m},@var{n}\@}
|
|
is 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, @samp{c[ad]\@{1,2\@}r} matches the strings @samp{car},
|
|
@samp{cdr}, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and
|
|
nothing else.@*
|
|
@samp{\@{0,1\@}} or @samp{\@{,1\@}} is equivalent to @samp{?}. @*
|
|
@samp{\@{0,\@}} or @samp{\@{,\@}} is equivalent to @samp{*}. @*
|
|
@samp{\@{1,\@}} is equivalent to @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 with
|
|
@samp{\@var{digit}} (see below).
|
|
@end 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.
|
|
|
|
@item \(?: @dots{} \)
|
|
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 @samp{\@var{digit}}.
|
|
|
|
Shy groups are particulary useful for mechanically-constructed regular
|
|
expressions because they can be added automatically without altering the
|
|
numbering of any ordinary, non-shy groups.
|
|
|
|
@item \@var{digit}
|
|
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
|
|
@samp{\1} 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 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 @samp{\@var{digit}} 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}.
|
|
|
|
@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}.
|
|
|
|
@item \c@var{c}
|
|
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.
|
|
|
|
@item \C@var{c}
|
|
matches any character whose category is not @var{c}.
|
|
@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.
|
|
|
|
@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
|
|
"[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
|
|
@end example
|
|
|
|
@noindent
|
|
In contrast, if you evaluate the variable @code{sentence-end}, you
|
|
will see the following:
|
|
|
|
@example
|
|
@group
|
|
sentence-end
|
|
@result{} "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[
|
|
]*"
|
|
@end group
|
|
@end example
|
|
|
|
@noindent
|
|
In this output, tab and newline appear as themselves.
|
|
|
|
This regular expression contains four parts in succession and can be
|
|
deciphered as follows:
|
|
|
|
@table @code
|
|
@item [.?!]
|
|
The first part of the pattern is a character alternative that matches
|
|
any one of three characters: period, question mark, and exclamation
|
|
mark. The match must begin with one of these three characters.
|
|
|
|
@item []\"')@}]*
|
|
The second part of the pattern matches any closing braces and quotation
|
|
marks, zero or more of them, that may follow the period, question mark
|
|
or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in
|
|
a string. The @samp{*} at the end indicates that the immediately
|
|
preceding regular expression (a character alternative, in this case) may be
|
|
repeated zero or more times.
|
|
|
|
@item \\($\\|@ $\\|\t\\|@ @ \\)
|
|
The third part of the pattern matches the whitespace that follows the
|
|
end of a sentence: the end of a line (optionally with a space), or a
|
|
tab, or two spaces. The double backslashes mark the parentheses and
|
|
vertical bars as regular expression syntax; the parentheses delimit a
|
|
group and the vertical bars separate alternatives. The dollar sign is
|
|
used to match the end of a line.
|
|
|
|
@item [ \t\n]*
|
|
Finally, the last part of the pattern matches any additional whitespace
|
|
beyond the minimum needed to end a sentence.
|
|
@end table
|
|
|
|
@node Regexp Functions
|
|
@subsection Regular Expression Functions
|
|
|
|
These functions operate on regular expressions.
|
|
|
|
@defun regexp-quote string
|
|
This function returns a regular expression whose only exact match is
|
|
@var{string}. Using this regular expression in @code{looking-at} will
|
|
succeed only if the next characters in the buffer are @var{string};
|
|
using it in a search function will succeed if the text being searched
|
|
contains @var{string}.
|
|
|
|
This allows you to request an exact string match or search when calling
|
|
a function that wants a regular expression.
|
|
|
|
@example
|
|
@group
|
|
(regexp-quote "^The cat$")
|
|
@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
|
|
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
|
|
This function returns the total number of grouping constructs
|
|
(parenthesized expressions) in @var{regexp}.
|
|
@end defun
|
|
|
|
@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 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.
|
|
@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.
|
|
|
|
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.
|
|
|
|
@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 &optional 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 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 buffer's end is used for @var{end}.
|
|
|
|
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{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:
|
|
@var{data}, and the number of replacements already made.
|
|
|
|
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.
|
|
|
|
If @var{from-string} contains upper-case letters, then
|
|
@code{perform-replace} 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 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 start and end positions of the 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 @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 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
|
|
|
|
These substitutions occur after case conversion, if any,
|
|
so the strings they substitute are never case-converted.
|
|
|
|
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, 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
|
|
@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. So don't try to rely on the value of the match data after
|
|
a failing search.
|
|
|
|
@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 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.
|
|
|
|
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.
|
|
@end defun
|
|
|
|
@defun match-string-no-properties count &optional in-string
|
|
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 or a repetition that repeated zero times.
|
|
@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
|
|
@ifnottex
|
|
number 2@var{n}
|
|
@end ifnottex
|
|
@tex
|
|
number {\mathsurround=0pt $2n$}
|
|
@end tex
|
|
corresponds to @code{(match-beginning @var{n})}; and
|
|
element
|
|
@ifnottex
|
|
number 2@var{n} + 1
|
|
@end ifnottex
|
|
@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{} (#<marker at 9 in foo>
|
|
#<marker at 17 in foo>
|
|
#<marker at 13 in foo>
|
|
#<marker at 17 in foo>)
|
|
@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}. (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.
|
|
|
|
@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.
|
|
|
|
This variable is used by passing it as an argument to the function
|
|
@code{replace-match}. @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
|
|
|
|
@ignore
|
|
arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f
|
|
@end ignore
|