Is there a function that joins a list of strings into a delimited string?

Question

Is there a function in Emacs Lisp that does the opposite of split-string, i.e. joins the elements of a list into string delimited by a given delimiter? In other words, is there a function that given a list, e.g. ("foo" "bar" "baz"), and a delimiter, e.g. ", ", returns that list as a string delimited by that delimiter, e.g. "foo, bar, baz".

Common Lisp seems to have such a function but the function with the same name in Emacs Lisp, format, is a wholly different function.

Answer 1

I think you are looking for mapconcat:

mapconcat applies function to each element of sequence: the results, which must be strings, are concatenated. Between each pair of result strings, mapconcat inserts the string separator. Usually separator contains a space or comma or other suitable punctuation.

Answer 2

Emacs has string-join since 24.4 as part of subr-x.el:

(eval-when-compile (require 'subr-x))
(string-join '("one" "two" "three") ", ") ; ==> "one, two, three"

subr-x.el contains also other useful (string manipulation) functions - from the 24.4 release notes:

New library subr-x.el for misc helper functions

hash-table-keys
hash-table-values
string-blank-p
string-empty-p
string-join
string-reverse
string-trim-left
string-trim-right
string-trim
string-remove-prefix
string-remove-suffix

Answer 3

If you use string manipulation heavily in your Elisp, i recommend you to install a library s.el, which has a vast and consistent API for strings. For your task it has a function s-join:

(s-join "+" '("abc" "def" "ghi")) ;; => "abc+def+ghi"
(s-join "\n" '("abc" "def" "ghi")) ;; => "abc\ndef\nghi"

Answer 4

Depending what you're doing, there may be a better function eg if you're building command line args, use combine-and-quote-strings which does the work for you.

(combine-and-quote-strings '("foo" "bar" "baz") ", ")
"foo, bar, baz"