Emacs Lisp: Match Data (Regex Result)

Emacs Lisp: Regex Functions store match result in match data. Such as caputured groups, or begin/end positions of the captured pattern, or whole matched string.

Match data can be accessed by the function match-data. However, elisp provide many more direct functions to extract data stored in match-data. Here are the most useful ones.

Get Match String (Captured Groups)

Whenever you call regex functions such as re-search-forward, string-match, replace-regexp-in-string, the captured text is stored in match-string.

match-string

(match-string NUM &optional STRING)

Return string of text matched by last search.

NUM an is integer.

• 0 means the whole matched text.
• 1 means first captured group.
• 2 means second captured group.
• etc.

If the last search is buffer text search, STRING should be nil. But if last regex search is done on a string by string-match, it should be the string that is searched.

;; example of match-string

(re-search-forward "id=\\([0-9]+\\)" )
(message "%s" (match-string 1 ))
;; prints 172

;; id=172

(setq xx "swimming in sea")

(string-match "\\([a-z]+?ing\\) " xx)

(match-string 1 xx)
;; "swimming"

match-string-no-properties

(match-string-no-properties n)

same as match-string but without Text Properties

(let ((case-fold-search nil))
  (re-search-forward "\\([0-9]+\\)")
  ;; lots text 123 abc
  (match-string-no-properties 1)
)
; "123"

Get Begin/End Positions (of Captured Groups)

match-beginning

(match-beginning n)

return the beginning position of the nth captured string of last regex search.

(let ((case-fold-search nil) p1 p2)
  (re-search-forward "\\([0-9]+\\)")
  (setq p1 (match-beginning 1))
  (setq p2 (match-end 1))
  (buffer-substring-no-properties p1 p2))
;; lots sample text 123 abc
;; "123"

match-end

(match-end n)

return the end position of the nth captured string of last regex search.

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