* Regexp Search:: Searching for a match for a regexp.
* POSIX Regexps:: Searching POSIX-style for the longest match.
* Search and Replace:: Internals of @code{query-replace}.
-* Match Data:: Finding out which part of the text matched
- various parts of a regexp, after regexp search.
+* Match Data:: Finding out which part of the text matched,
+ after a string or regexp search.
* Searching and Case:: Case-independent or case-significant searching.
* Standard Regexps:: Useful regexps for finding sentences, pages,...
@end menu
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, leaving point where it started.
+the search fails, with results depending on the value of
+@var{noerror}, as described above.
@end deffn
@deffn Command search-backward string &optional limit noerror repeat
an error if the search fails. If @var{noerror} is @code{t}, then it
returns @code{nil} instead of signaling an error. If @var{noerror} is
neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the
-end of the buffer) and returns @code{nil}.
+end of the accessible portion of the buffer) and returns @code{nil}.
If @var{repeat} is non-@code{nil}, then the search is repeated that many
times. Point is positioned at the end of the last match.
@menu
* Syntax of Regexps:: Rules for writing regular expressions.
-* Regexp Functions:: Functions for operating on regular expressions.
* Regexp Example:: Illustrates regular expression syntax.
+* Regexp Functions:: Functions for operating on regular expressions.
@end menu
@node Syntax of Regexps
The next alternative is for @samp{a*} to match only two @samp{a}s. With
this choice, the rest of the regexp matches successfully.@refill
-Nested repetition operators can be extremely slow if they specify
-backtracking loops. For example, it could take hours for the regular
-expression @samp{\(x+y*\)*a} to try to match the sequence
-@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately fails.
-The slowness is because Emacs must try each imaginable way of grouping
-the 35 @samp{x}s before concluding that none of them can work. To make
-sure your regular expressions run fast, check nested repetitions
+Nested repetition operators can be extremely slow or loop infinitely
+if they use repetition operators inside repetition operators. For
+example, it could take hours for the regular expression
+@samp{\(x+y*\)*a} to try to match the sequence
+@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately
+fails. Emacs must try each way of grouping the 35 @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.
@item @samp{+}
You can also include character ranges in a character alternative, by
writing the starting and ending characters with a @samp{-} between them.
-Thus, @samp{[a-z]} matches any lower-case @sc{ascii} letter. Ranges may be
-intermixed freely with individual characters, as in @samp{[a-z$%.]},
-which matches any lower case @sc{ascii} letter or @samp{$}, @samp{%} or
-period.
+Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter.
+Ranges may be intermixed freely with individual characters, as in
+@samp{[a-z$%.]}, which matches any lower case @acronym{ASCII} letter
+or @samp{$}, @samp{%} or period.
Note that the usual regexp special characters are not special inside a
character alternative. A completely different set of characters is
@var{c1} is the first character of the charset to which @var{c2}
belongs.
-You cannot always match all non-@sc{ascii} characters with the regular
+You cannot always match all non-@acronym{ASCII} 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 non-@sc{ascii} characters have codes
+buffer or string, because many non-@acronym{ASCII} characters have codes
above octal 0377. However, the regular expression @code{"[^\000-\177]"}
-does match all non-@sc{ascii} characters (see below regarding @samp{^}),
+does match all non-@acronym{ASCII} characters (see below regarding @samp{^}),
in both multibyte and unibyte representations, because only the
-@sc{ascii} characters are excluded.
+@acronym{ASCII} characters are excluded.
Starting in Emacs 21, a character alternative can also specify named
character classes (@pxref{Char Classes}). This is a POSIX feature whose
@item @samp{^}
@cindex beginning of line in regexp
-is a special character that matches the empty string, but only at the
-beginning of a line in the text being matched. Otherwise it fails to
-match anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at
-the beginning of a line.
+When matching a 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.
@item @samp{$}
@cindex @samp{$} in regexp
@cindex end of line in regexp
-is similar to @samp{^} but matches only at the end of a line. Thus,
-@samp{x+$} matches a string of one @samp{x} or more at the end of a line.
+is similar to @samp{^} but matches only at the end of a line (or the
+end of the accessible portion of the buffer). Thus, @samp{x+$}
+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.
@table @samp
@item [:ascii:]
-This matches any @sc{ascii} (unibyte) character.
+This matches any @acronym{ASCII} (unibyte) character.
@item [:alnum:]
This matches any letter or digit. (At present, for multibyte
characters, it matches anything that has word syntax.)
@item [:blank:]
This matches space and tab only.
@item [:cntrl:]
-This matches any @sc{ascii} control character.
+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 @sc{ascii} control
+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-@sc{ascii} (multibyte) character.
+This matches any non-@acronym{ASCII} (multibyte) character.
@item [:print:]
-This matches printing characters---everything except @sc{ascii} control
+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
@samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on.
@item \@{@var{m},@var{n}\@}
-is more general postfix operator that specifies repetition with a
+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.
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
+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.
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 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.
+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.
@table @samp
@item \`
@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
+@samp{\b} matches at the beginning or end of the buffer (or string)
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.
+end of a word, nor at the beginning or end of the buffer (or string).
@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
+@samp{\<} matches at the beginning of the buffer (or string) 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.
+matches at the end of the buffer (or string) only if the contents end
+with a word-constituent character.
+
+@item \_<
+@cindex @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.
+
+@item \_>
+@cindex @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.
@end table
@kindex invalid-regexp
@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}.
+ Here is a complicated regexp which was formerly used by Emacs to
+recognize the end of a sentence together with any whitespace that
+follows. It was used as the variable @code{sentence-end}. (Its value
+nowadays contains alternatives for @samp{.}, @samp{?} and @samp{!} in
+other character sets.)
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
tab and @samp{\n} for a newline.
@example
-"[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
@end example
@noindent
-In contrast, if you evaluate the variable @code{sentence-end}, you
-will see the following:
+In contrast, if you evaluate this string, you will see the following:
@example
@group
-sentence-end
- @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[
+"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
+ @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[
]*"
@end group
@end example
@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.
+mark. The match must begin with one of these three characters. (This
+is the one point where the new value of @code{sentence-end} differs
+from the old. The new value also lists sentence ending
+non-@acronym{ASCII} characters.)
@item []\"')@}]*
The second part of the pattern matches any closing braces and quotation
@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.
+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 non-@code{nil}, then the
returned regular expression is always enclosed by at least one
-parentheses-grouping construct.
+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
@defun regexp-opt-depth regexp
This function returns the total number of grouping constructs
-(parenthesized expressions) in @var{regexp}.
+(parenthesized expressions) in @var{regexp}. (This does not include
+shy groups.)
@end defun
@node Regexp Search
@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}.
+accessible portion 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
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.
+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
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}.
+instead, and the end of the buffer's accessible portion 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{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.
+@var{replacements} list before advancing cyclically 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
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}.
+
+@strong{Usage note:} Do not use this function in your own programs
+unless you want to do something very similar to what
+@code{query-replace} does, including setting the mark and possibly
+querying the user. For most purposes a simple loop like, for
+instance:
+
+@example
+(while (re-search-forward "foo[ \t]+bar" nil t)
+ (replace-match "foobar"))
+@end example
+
+@noindent
+is preferable. It runs faster and avoids side effects, such as
+setting the mark. @xref{Replacing Match,, Replacing the Text that
+Matched}, for a description of @code{replace-match}.
@end defun
@defvar query-replace-map
@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.
+text found during a 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
@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}.
+for @var{string} and make sure that the current buffer when you call
+@code{replace-match} 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
@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{\(@dots{}\)}.
+If the @var{n}th subexpression never matched, an empty string is substituted.
@item @samp{\\}
@cindex @samp{\} in replacement
The functions @code{match-data} and @code{set-match-data} read or
write the entire match data, all at once.
-@defun match-data
+@defun match-data &optional integers reuse
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
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}.
+buffer and all are integers or @code{nil} if matching was done on a
+string with @code{string-match}. If @var{integers} is
+non-@code{nil}, then the elements are integers or @code{nil}, even if
+matching was done on a buffer. 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. Also,
+@code{match-beginning} and
+@code{match-end} always return integers or @code{nil}.
+
+If @var{reuse} is non-@code{nil}, it should be a list. In that case,
+@code{match-data} stores the match data in @var{reuse}. That is,
+@var{reuse} 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
+@code{nil}. The purpose of this feature is to avoid producing too
+much garbage, that would later have to be collected.
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
@defmac save-match-data body@dots{}
This macro executes @var{body}, saving and restoring the match
-data around it.
+data around it. The return value is the value of the last form in
+@var{body}.
@end defmac
You could use @code{set-match-data} together with @code{match-data} to
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 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 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}.
@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).
+@w{@code{"\f\\|[ \t]*$"}}, which matches a line containing only
+whitespace or starting with a form feed (after its left margin).
@end defvar
@defvar sentence-end
This is the regular expression describing the end of a sentence. (All
-paragraph boundaries also end sentences, regardless.) The default value
-is:
+paragraph boundaries also end sentences, regardless.) The (slightly
+simplified) default value is:
@example
-"[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
+"[.?!][]\"')@}]*\\($\\| $\\|\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.
+This means a period, question mark or exclamation mark (the actual
+default value also lists their alternatives in other character sets),
+followed optionally by closing parenthetical characters, followed by
+tabs, spaces or new lines.
For a detailed explanation of this regular expression, see @ref{Regexp
Example}.