34.4 Regular Expression Searching

In GNU Emacs, you can search for the next match for a regular expression either incrementally or not. For incremental search commands, see (emacs)Regexp Search section `Regular Expression Search' dans The GNU Emacs Manual. Here we describe only the search functions useful in programs. The principal one is 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. Voir la section Text Representations.

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 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-forward does when the search fails depends on the value of noerror:

nil

Signal a search-failed error.

t

Do nothing and return nil.

anything else

Move point to limit (or the end of the accessible portion of the buffer) and return nil.

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 ----------

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 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-forward finds the match whose beginning is as close as possible to the starting point. If 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 (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-forward would require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that.

Function: string-match regexp string &optional start

This function returns the index of the start of the first match for the regular expression regexp in string, or nil if 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). Voir la section The Match Data.

(string-match "quick" "The quick brown fox jumped quickly." 8) ⇒ 27 (match-end 0) ⇒ 32

Function: looking-at regexp

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 t if so, nil otherwise.

This function does not move point, but it updates the match data, which you can access using match-beginning and match-end. Voir la section The Match Data.

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

Function: looking-back regexp &optional limit

This function returns t if regexp matches text before point, ending at point, and nil otherwise.

Because regular expression matching works only going forward, this is implemented by searching backwards from point for a match that ends at point. That can be quite slow if it has to search a long distance. You can bound the time required by specifying limit, which says not to search before limit. In this case, the match that is found must begin at or after 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

Variable: search-spaces-regexp

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 search-spaces-regexp.

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.

Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.