In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not. For incremental search
commands, see Regular Expression Search. Here we describe only the search functions
useful in programs. The principal one is
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. See Text Representations.
This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first match found. It returns the new value of point.
If limit is non-
nil, it must be a position in the current buffer. It specifies the upper bound to the search. No match extending after that position is accepted.
If repeat is supplied, it must be a positive number; the search is repeated that many times; each repetition starts at the end of the previous match. If all these successive searches succeed, the search succeeds, moving point and returning its new value. Otherwise the search fails. What
re-search-forwarddoes when the search fails depends on the value of noerror:
- Signal a
- Do nothing and return
- anything else
- Move point to limit (or the end of the accessible portion of the buffer) and return
In the following example, point is initially before the ‘T’. Evaluating the search call moves point to the end of that line (between the ‘t’ of ‘hat’ and the newline).---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) ⇒ 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found.
This function is analogous to
re-search-forward, but they are not simple mirror images.
re-search-forwardfinds the match whose beginning is as close as possible to the starting point. If
re-search-backwardwere a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible (and yet ends before the starting point). The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position.
A true mirror-image of
re-search-forwardwould require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that.
This function returns the index of the start of the first match for the regular expression regexp in string, or
nilif there is no match. If start is non-
nil, the search starts at that index in string.
For example,(string-match "quick" "The quick brown fox jumped quickly.") ⇒ 4 (string-match "quick" "The quick brown fox jumped quickly." 8) ⇒ 27
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
(match-end 0). See Match Data.(string-match "quick" "The quick brown fox jumped quickly." 8) ⇒ 27 (match-end 0) ⇒ 32
This predicate function does what
string-matchdoes, but it avoids modifying the match data.
This function determines whether the text in the current buffer directly following point matches the regular expression 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
This function does not move point, but it does update the match data. See Match Data. If you need to test for a match without modifying the match data, use
looking-at-p, described below.
In this example, point is located directly before the ‘T’. If it were anywhere else, the result would be
nil.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") ⇒ t
This function returns
tif regexp matches the text immediately before point (i.e., ending at point), and
Because regular expression matching works only going forward, this is implemented by searching backwards from point for a match that ends at point. That can be quite slow if it has to search a long distance. You can bound the time required by specifying limit, which says not to search before limit. In this case, the match that is found must begin at or after limit.
If greedy is non-
nil, this function extends the match backwards as far as possible, stopping when a single additional previous character cannot be part of a match for regexp. When the match is extended, its starting position is allowed to occur before limit.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-back "read \"" 3) ⇒ t (looking-back "read \"" 4) ⇒ nil
As a general recommendation, try to avoid using
looking-backwherever possible, since it is slow. For this reason, there are no plans to add a
This predicate function works like
looking-at, but without updating the match data.
If this variable is non-
nil, it should be a regular expression that says how to search for whitespace. In that case, any group of spaces in a regular expression being searched for stands for use of this regular expression. However, spaces inside of constructs such as ‘[...]’ and ‘*’, ‘+’, ‘?’ are not affected by
Since this variable affects all regular expression search and match constructs, you should bind it temporarily for as small as possible a part of the code.