@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}.
+contains @var{string}. @xref{Regexp Search}.
This allows you to request an exact string match or search when calling
a function that wants a regular expression.
This function returns an efficient regular expression that will match
any of the strings in the list @var{strings}. This is useful when you
need to make matching or searching as fast as possible---for example,
-for Font Lock mode.
+for Font Lock mode@footnote{Note that @code{regexp-opt} does not
+guarantee that its result is absolutely the most efficient form
+possible. A hand-tuned regular expression can sometimes be slightly
+more efficient, but is almost never worth the effort.}.
+@c See eg http://debbugs.gnu.org/2816
If the optional argument @var{paren} is non-@code{nil}, then the
returned regular expression is always enclosed by at least one
(but not as efficient):
@example
-(defun regexp-opt (strings paren)
+(defun regexp-opt (strings &optional paren)
(let ((open-paren (if paren "\\(" ""))
(close-paren (if paren "\\)" "")))
(concat open-paren
shy groups (@pxref{Regexp Backslash}).
@end defun
+@c Supposedly an internal regexp-opt function, but table.el uses it at least.
+@defun regexp-opt-charset chars
+This function returns a regular expression matching a character in the
+list of characters @var{chars}.
+
+@example
+(regexp-opt-charset '(?a ?b ?c ?d ?e))
+ @result{} "[a-e]"
+@end example
+@end defun
+
+@c Internal functions: regexp-opt-group
+
@node Regexp Search
@section Regular Expression Searching
@cindex regular expression searching
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}.
+This function does not move point, but it does update the match data.
@xref{Match Data}. If you need to test for a match without modifying
the match data, use @code{looking-at-p}, described below.
@end defun
@defun looking-back regexp &optional limit greedy
-This function returns @code{t} if @var{regexp} matches text before
-point, ending at point, and @code{nil} otherwise.
+This function returns @code{t} if @var{regexp} matches the text
+immediately before point (i.e., ending at point), and @code{nil} otherwise.
Because regular expression matching works only going forward, this is
implemented by searching backwards from point for a match that ends at
@result{} nil
@end group
@end example
+
+@c http://debbugs.gnu.org/5689
+As a general recommendation, try to avoid using @code{looking-back}
+wherever possible, since it is slow. For this reason, there are no
+plans to add a @code{looking-back-p} function.
@end defun
@defun looking-at-p regexp
@node POSIX Regexps
@section POSIX Regular Expression Searching
+@cindex backtracking and POSIX regular expressions
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
query the match data immediately after searching, before calling any
other function that might perform another search. Alternatively, you
may save and restore the match data (@pxref{Saving Match Data}) around
-the call to functions that could perform another search.
+the call to functions that could perform another search. Or use the
+functions that explicitly do not modify the match data;
+e.g. @code{string-match-p}.
+@c This is an old comment and presumably there is no prospect of this
+@c changing now. But still the advice stands.
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.
+current implementation, it does not, but we may change it in the
+future. 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
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.
+matching. Failure to follow this advice will lead to incorrect results.
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
@end defun
@defun match-beginning count
-This function returns the position of the start of text matched by the
+This function returns the position of the start of the 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
@defun match-data &optional integers reuse reseat
This function returns a list of positions (markers or integers) that
-record all the information on what text the last search matched.
+record all the information on the text that 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
If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list
are reseated to point to nowhere.
+@c TODO Make it properly obsolete.
@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
+ When you call a function that may 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:
@group
(re-search-forward "The \\(cat \\)")
@result{} 48
-(foo) ; @r{Perhaps @code{foo} does}
- ; @r{more searching.}
+(foo) ; @r{@code{foo} does more searching.}
(match-end 0)
@result{} 61 ; @r{Unexpected result---not 48!}
@end group
@code{replace-regexp-in-string} calls @var{rep} for each match,
passing the text of the match as its sole argument. It collects the
value @var{rep} returns and passes that to @code{replace-match} as the
-replacement string. The match-data at this point are the result
+replacement string. The match data at this point are the result
of matching @var{regexp} against a substring of @var{string}.
@end defun
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.
+it uses the @var{replacements} without altering their case.
Normally, the keymap @code{query-replace-map} defines the possible
user responses for queries. The argument @var{map}, if
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.''
+event and look it up ``by hand''.
@end itemize
@end defvar
@table @code
@item act
-Do take the action being considered---in other words, ``yes.''
+Do take the action being considered---in other words, ``yes''.
@item skip
-Do not take action for this question---in other words, ``no.''
+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.''
+Answer this question ``no'', and give up on the entire series of
+questions, assuming that the answers will be ``no''.
+
+@item exit-prefix
+Like @code{exit}, but add the key that was pressed to
+@code{unread-comment-events}.
@item act-and-exit
-Answer this question ``yes,'' and give up on the entire series of
-questions, assuming that subsequent answers will be ``no.''
+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
+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.
+``yes'', without further user interaction.
@item backup
Move back to the previous place that a question was asked about.
Enter a recursive edit to deal with this question---instead of any
other action that would normally be taken.
+@item edit-replacement
+Edit the replacement for this question in the minibuffer.
+
@item delete-and-edit
Delete the text being considered, then enter a recursive edit to replace
it.
@defvar multi-query-replace-map
This variable holds a keymap that extends @code{query-replace-map} by
providing additional keybindings that are useful in multi-buffer
-replacements.
+replacements. The additional ``bindings'' are:
+
+@table @code
+@item automatic-all
+Answer this question and all subsequent questions in the series with
+``yes'', without further user interaction, for all remaining buffers.
+
+@item exit-current
+Answer this question ``no'', and give up on the entire series of
+questions for the current buffer. Continue to the next buffer in the
+sequence.
+@end table
@end defvar
@defvar replace-search-function
the end of a sentence, including the whitespace following the
sentence. (All paragraph boundaries also end sentences, regardless.)
-If the value is @code{nil}, the default, then the function
-@code{sentence-end} has to construct the regexp. That is why you
+If the value is @code{nil}, as it is by default, then the function
+@code{sentence-end} constructs the regexp. That is why you
should always call the function @code{sentence-end} to obtain the
regexp to be used to recognize the end of a sentence.
@end defopt
if non-@code{nil}. Otherwise it returns a default value based on the
values of the variables @code{sentence-end-double-space}
(@pxref{Definition of sentence-end-double-space}),
-@code{sentence-end-without-period} and
+@code{sentence-end-without-period}, and
@code{sentence-end-without-space}.
@end defun
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