A peek at Emacs 24.4: New string manipulation functions

Emacs has often been criticized for failing to provide a more extensive string manipulation API (compared to that of programming languages like Ruby and Perl, for instance). As many programs (extensions) running on top of it are doing quite a lot of string manipulation, having a good string API is important. To compensate the lack of certain primitives in Emacs itself a lot of package authors are using these days packages like s.el or simply adding the string functions they need directly to their packages (to reduce the number of third-party deps).

In Emacs 24.4 finally the situation is improving. Finally, we’re getting string-suffix-p, which was mysteriously missing even though string-prefix-p has been part of Emacs for years:

(string-suffix-p "test" "my_test")
; => t
(string-suffix-p "tester" "my_test")
; => nil

More importantly, Emacs 24.4 ships with a new built-in library called subr-x, which features a bunch of other string manipulation functions:

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

Here’s a brief demo of them in action:

;; all functions in the library are defined as inline, so you don't
;; need to require the library at runtime
(eval-when-compile (require 'subr-x))

(string-empty-p "")
; => t
(string-empty-p "  ")
; => nil
(string-blank-p "  ")
; => 0 (#o0, #x0, ?\C-@)
(string-reverse "Batman")
; => "namtaB"
(string-join '("one" "two" "three"))
; => "onetwothree"
(string-join '("one" "two" "three") ",")
; => "one,two,three"
(string-trim "   Peter Parker ")
; => "Peter Parker"
(string-remove-prefix "Mr. " "Mr. Smith")
; => "Smith"
(string-remove-suffix "Smith" "Mr. Smith")
; => "Mr. "

Sure, subr-x is not as extensive as s.el (and will never be), but I think that it’s a big step in the right direction. It’s likely that subr-x will be extended in subsequent Emacs versions and some of the functions from it will be promoted to built-in.

That’s all I have for now. Until next time!