Emacs Lisp: String Functions

Basic String Functions

length

(length SEQUENCE)
Return the length of vector, list or string SEQUENCE.

(length "abc")
;; 3

substring

(substring STRING &optional FROM TO)
return a substring from position FROM to TO. Position start at 0. By default, TO is to end of string, if omitted. FROM is 0. If negative, count from right.

(substring "abc123" 0 3)
;; "abc"

concat

(concat &rest SEQUENCES)
Concatenate all the arguments and make the result a string.

(concat "some" "thing")

split-string

(split-string STRING &optional SEPARATORS OMIT-NULLS TRIM)
Split STRING into substrings bounded by matches for SEPARATORS.

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

String To/From Number

(string-to-number "3")

(number-to-string 3)

(format "%d" 3)
 ;; same as number-to-string but can also do format

Buffer Text to String

Emacs Lisp: Get Buffer String

String to Buffer

If you got a long string, and need to insert or delete parts often, it's much more efficient to use buffer data type.

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))

Match String by Regex

string-match

(string-match REGEXP STRING &optional START)
Return index of start of first match for REGEXP in STRING, or nil.

(string-match "b+" "abbc")
;; 1

Get Substring by Regex

Use match-string.

(setq myStr "swimming in pool")

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

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

Regex Replace in String

replace-regexp-in-string

(replace-regexp-in-string REGEXP REP STRING &optional FIXEDCASE LITERAL SUBEXP START)
Replace string by regex.

(replace-regexp-in-string "</*div>" "<p>" "<div>something</div>")
;; return
;; "<p>something<p>"

See:

• Emacs Lisp: Find Replace String in Buffer
• Emacs Lisp: Regex Tutorial

Trim String and Others

These are new in Emacs 24.4 (released 2014-10). To use them, you need to first:

(require 'subr-x)

• string-blank-p
• string-empty-p
• string-join
• string-reverse
• string-trim-left
• string-trim-right
• string-trim
• string-remove-prefix
• string-remove-suffix

(require 'subr-x)
(string-trim " abc  ")

(info "(elisp) Strings and Characters")

String Functions Reference

Here's a complete list of string functions for reference. If you are a elisp beginner, ignore them.

• stringp
• string-or-null-p
• char-or-string-p

(info "(elisp) Predicates-for-Strings")

• make-string
• string → chars to string
• substring-no-properties
• concat
• split-string-default-separators

(info "(elisp) Creating-Strings")

• store-substring → modify string
• clear-string

(info "(elisp) Modifying-Strings")

• char-equal
• string-equal
• string-collate-equalp
• string-greaterp
• string-collate-lessp
• string-version-lessp
• string-prefix-p
• string-suffix-p
• compare-strings

• string-distance
• assoc-string

(info "(elisp) Text-Comparison")

• number-to-string
• string-to-number
• char-to-string
• string-to-char
• concat
• vconcat → string into a vector
• append → string into a list
• byte-to-string

(info "(elisp) Text-Comparison")

• downcase
• upcase
• capitalize
• upcase-initials

(info "(elisp) Case-Conversion")

• case-table-p
• set-standard-case-table
• standard-case-table
• current-case-table
• set-case-table
• set-case-syntax-pair
• set-case-syntax-delims
• set-case-syntax
• with-case-table
• ascii-case-table
• describe-buffer-case-table

(info "(elisp) Case-Tables")