An example of "light" validation of babashka.cli arguments i.e. checking for required arguments without using Spec or Malli

cli-gist.clj

(ns cli-gist
  (:require [babashka.cli :as cli]
            [clojure.set :as set]
            [clojure.string :as str]))


(def upload-spec {:bucket-region {:ref      "<aws-region>"
                                  :desc     "The AWS region where the S3 bucket was created"
                                  :optional true
                                  :alias    :r}
                  :bucket        {:ref      "<s3-bucket-name>"
                                  :desc     "The name of the s3 bucket"
                                  :optional false
                                  :alias    :b}
                  :path          {:ref      "<s3-path>"
                                  :desc     "The path inside the s3 bucket where the artifact will be added"
                                  :optional false
                                  :alias    :p}})

(defn validate-optional-args
  "return a string describing missing CLI arguments using the :optional key in a spec"
  [{:keys [spec parsed]}]
  (let [required-keys (->> spec
                           (keep (fn [arg-entry]
                                   (when (false? (:optional (val arg-entry)))
                                     (key arg-entry))))
                           set)
        parsed-keys (set (keys parsed))]
    (when-let [missing-keys (seq (set/difference required-keys parsed-keys))]
      (->> missing-keys
           sort
           (map name)
           (str/join ", ")
           (str "Required keys missing: ")))))

(defn parse-deploy-args
  "parse and validate the cli args"
  [args]
  (let [opts (cli/parse-opts args {:spec upload-spec})]
    (when-let [validation-error (validate-optional-args {:spec   upload-spec
                                                         :parsed opts})]
      (println validation-error "\n")
      (println "Usage:")
      (println (cli/format-opts {:spec deploy-spec}))
      (throw (ex-info "failed" {:message validation-error})))
    opts))

(comment

  ; good
  (parse-deploy-args ["--bucket-region" "us-west-2"
                      "--bucket" "cloudfront-assets"
                      "--path" "apps/prod"])

  ; bad
  (parse-deploy-args ["--bucket-region" "us-west-2"])

  )