Elisp: String Functions

By Xah Lee. Date: . Last updated: .

Here are the most basic string functions in elisp.

Length

;; length
(length "abc") ; returns 3

Substring

;; Extract a substring
(substring myStr myStartPos myEndPos)

Join Strings

;; join strings
(concat "some" "thing")

Match String by Regex

;; check if a string matches a pattern
(string-match myRegex myStr)

See also:

Get Captured String from Regex Match

In emacs, most functions that take a regex argument, after being called, will save/modify info in “match data”, such as caputured groups.

Match data can be accessed by the function match-data, and other functions.

The most useful is match-string, which returns the captured string.

;; get captured match
;; second argument is optional, but required if the last match is done by “string-match”
(match-string 1 myStr)

Replace in String

;; change a given string using regex. Returns changed string.
(replace-regexp-in-string myRegex myReplacement myStr)

Split String

;; split string into parts, returns a list
(split-string "xy_007_cat" "_")

String To/From Number

(string-to-number "3") ; change datatype
(number-to-string 3) ; convert to string
(format "%d" 3) ; similar to number-to-string but with fine control

Buffer Text to String

Elisp: Get Buffer String

String to Buffer

Emacs has only a few functions that takes a string as argument. Any non-trivial string processing is done with a buffer.

If you got a big string already somehow, you can put into a buffer by using with-temp-buffer, then insert your string, process it, then use buffer-string to get the whole buffer content.

;; process string in a temp buffer

(with-temp-buffer
  (insert bigString)

  (goto-char (point-min))

  ;; code to manipulate string. eg delete char, etc

  ;; return whole buffer string
  (buffer-string))

Trim String and Others

Emacs 24.4 added many string functions. [see Emacs 24.4 New Features (released 2014-10)]

These are new string functions:

To use them, you need to first (require 'subr-x).

(require 'subr-x)
(string-trim " something  ") ; ⇒ "something"

Note: these functions are not documented and are kinda experimental. In the file header, it says it shouldn't be documented.

;; Do not document these functions in the lispref.
;; http://lists.gnu.org/archive/html/emacs-devel/2014-01/msg01006.html

(info "(elisp) Strings and Characters")

Elisp Basic Functions

  1. Cursor
  2. Text Editing
  3. Get Buffer String
  4. String Functions
  5. Buffer and File
  6. File and Directory
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