Using Clojure tools.cli, how do I validate that only acceptable options were passed?

Question

My CLI tool has options, for example -a -b and -c .

If a user passes -d , I want to fail with an error message. Of course I could code up an ad-hoc check, but how do I do this with tools.cli ?

Answer 1

Errors are communicated in the result of parse-opts . This means, it's your responsibility to actually fail in the case, you don't accept arbitrary arguments.

Eg

(require '[clojure.tools.cli :refer [parse-opts]])

(def cli-options
  [["-a" "--aye" "A"]
   ["-b" "--bee" "B"]])

(parse-opts *command-line-args* cli-options)

Running with (for the sake of brevity, I use babashka, formatting is mine):

% bb x.bb -a -b -d
{:options {:aye true, 
           :bee true}, 
 :arguments [], 
 :summary "  -a, --aye  A\n  -b, --bee  B", 
 :errors ["Unknown option: \"-d\""]}

As you can see, there is a key :errors and it points to a vector of strings with all the errors.

If you need inspiration for how to deal with the common case of writing a "main" function, that behaves properly (eg show the usage, fail on error...) I suggest a peek at the "Example Usage" section of tools.cli