Check if a string ends with a suffix in Emacs Lisp

Question

Is there a function that checks that a string ends with a certain substring? Python has endswith:

>>> "victory".endswith("tory")
True

Answer 1

Just install s.el string manipulation library and use its s-suffix? predicate:

(s-suffix? "turn." "...when it ain't your turn.") ; => t

But if you refuse you to use this library, you have to write your own function. There is string-prefix-p, which is an analog to Python's str.startswith, in subr.el, and it is just a wrapper around compare-strings. According to Emacs 24.3 changelog:

** New function `string-prefix-p'.
(This was actually added in Emacs 23.2 but was not advertised at the time.)

string-suffix-p was added only in Emacs 24.4, so for earlier versions i wrote:

(defun string-suffix-p (str1 str2 &optional ignore-case)
  (let ((begin2 (- (length str2) (length str1)))
        (end2 (length str2)))
    (when (< begin2 0) (setq begin2 0))
    (eq t (compare-strings str1 nil nil
                           str2 begin2 end2
                           ignore-case))))

(when (< begin2 0) (setq begin2 0)) is a workaround, because if you pass negative numbers to compare-strings, it barfs with *** Eval error *** Wrong type argument: wholenump, -1.

If you byte compile the function, it works faster than yves Baumes solution, even though string-match is a C function.

ELISP> (setq str1 "miss."
             str2 "Ayo, lesson here, Bey. You come at the king, you best not miss.")
ELISP> (benchmark-run 1000000 (string-suffix-p str1 str2))
(4.697675135000001 31 2.789847821000066)
ELISP> (byte-compile 'string-suffix-p)
ELISP> (benchmark-run 1000000 (string-suffix-p str1 str2))
(0.43636462600000003 0 0.0)
ELISP> (benchmark-run 1000000 (string-match "miss\.$" str2))
(1.3447664240000001 0 0.0)