Google flags ("gflags") for Clojure. See https://github.com/gflags/python-gflags.

The Google approach to command-line flags is that they are defined in the source file in which they are used. This means that in a situation with lots of code sharing, where you may have 3 or 4 command-line apps that all use one common module, the common module can define its own command line flags, which then get used by each app.

It may sound a little weird, but in practice it works well and can be very convenient.

In this translation of the concept to clojure, each namespace can define its own flags.

[com.lemonodor/gflags "0.7.3"]

Say you have a namespace for your S3 utilities. You can define some flags in that namespace for your AWS credentials etc.:

(ns s3-utils
  "Utilties for accessing AWS S3."
  (:require [com.lemonodor.gflags :as gflags])
  ...)

(gflags/define-string "aws-access-key"
  nil
  "The AWS access key to use.")
(gflags/define-string "aws-secret-key"
  nil
  "The AWS secret key to use.")
(gflags/define-integer "num-retries"
  3
  "The number of times to retry S3 operations.")

(defn get-s3-file [url & {:keys [access-key secret-key num-retries]}]
  (let [access-key (or access-key (gflags/flags :aws-access-key))
        secret-key (or secret-key (gflags/flags :aws-secret-key))]
    ...))

Then in a CLI app namespace, you just need to call parse-flags:

(ns main-app
  "Command-line app"
  (:require [com.lemonodor.gflags :as gflags])
  ...)

(defn -main [& args]
  (let [unparsed-args (gflags/parse-flags (into ["argv0"] args))]
    ...))

This code is under development (but can definitely be useful in its current state).

• Flag types: define-string, define-boolean, define-integer, define-float, define-enum, define-list, define-multi-string, define-multi-integer, define-multi-float.
• Long names (:name) and short names (:short-name).
• Required flags (:required? true)
• --flagfile
• Errors if a flag with the same name is registered in two different namespaces.

• --help, --helpshort, --helpxml, --undefok.
• Flag serialization.
• Flag validators.
• "spaceseplist" flags.

To run tests:

$ lein test