String equality, ignore case?

Question

Q: how does one test string equality but ignore case?

I've got a situation in which I'd like to compare strings but ignore case. Case is significant for string-equal, and apparently is insensitive to case-fold-search:

(string-equal "string" "StrinG")        ; => nil
(let ((case-fold-search t))
  (string-equal "string" "StrinG"))     ; => nil

I could always preprocess the strings (say, with downcase) before comparing them:

(string-equal (downcase "string")
              (downcase "StrinG"))      ; => t

But that seems like overkill to do two extra function calls every time. Have I overlooked the relevant predicate function somewhere?

Answer 1

You can use compare-strings:

(compare-strings STR1 START1 END1 STR2 START2 END2 &optional IGNORE-CASE)

Use nils for starts and ends to use the whole strings.

Answer 2

Another short alternative:

(cl-equalp "string" "strinG")      ; => t
(cl-equalp "strinG" "this string") ; => nil 
(cl-equalp "word" "buzzword")      ; => nil

equalp from the deprecated cl library is another alternative. From (documentation 'cl-equalp), my emphasis in bold:

like ‘equal’, except that it accepts numerically equal numbers of different types (float vs. integer), and also compares strings case-insensitively.

Answer 3

Use string-suffix-p:

(string-suffix-p "string" "strinG" t)

Much simpler and doesn't require 4 nils. It doesn't test if strings are equal per se ((string-suffix-p "word" "buzzword" t) ⇒ t). Although, in some cases this should be sufficient (if you have limited dictionary to check upon).