Skip to content


Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Option management for Clojure
branch: master

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.


Manage your options.


  • It's epic good at command line args.
  • If you've got config files, just load them into a map and merge them.
  • Declare options public or private, i.e. whether or not the end-user is able to modify them.
  • Define parsers, validators, and mergers for individual options.
  • It throws exceptions when people do stupid things.
  • If your project is super-duper complex, set up individual config namespaces for different parts of it.
  • It's probably the best Clojure library that does exactly what it does.



[org.dave/cfg "1.0.0"]


The Midje test suite reads much like a tutorial.

Quick Example

Make a separate namespace for handling all your config needs

(ns my-proj.cfg
  (:use cfg.core))

(init) ; this just evals src/cfg/cfg.clj in my-proj.cfg

Now you can define you option tree with defopt and defopts

(defopt :num-cats
  :default     50
  :parse       #(Long. %)  ; this gets called when parsing options from command line
  :validate    #(>= % 1)   ; IllegalArgumentException when this returns false
  :help-string "The number of cats to use."  ; this gets used by the fn print-help
  :aliases     ["c" "-cats"]) ; causes -c or --cats to be used as unix-style cli args.

defopts lets you nest options inside a container map

(defopts :data-paths

  (defopt :dictionary
    :default  "/usr/share/dict/words"
    :validate #(.isFile ( %)) 
    :aliases  ["d" "-dict"]
    :help-string "Where the dictionary at?")

  (defopt :cat-photo-dir
    ; you don't need to specify a default
    :private true)) ; means that this opt can't be set when parsing cli args.

To specify that an option should be a boolean flag, use :bool true

(defopt :use-catnip
  :bool    true
  :default false
  :aliases ["n" "-catnip"]
  :help-string "Enables happy mode.")

If the user specifies -n, :use-catnip gets set to (notwhatever it currently is).

You can also specify that options should be merged.

(defopt :cat-names
  :default ["muggins" "felix"]
  :parse   #(clojure.string/split % #",")
  :merge   into)

The merge funciton gets called with the current value first.

All of this translates to:

  :data-paths {
    :dictionary "/usr/share/dict/words"
    :cat-photo-dir nil
  :num-cats   50
  :use-catnip false
  :cat-names  ["muggins" "felix"]

Now require the namespace you just created

(ns my-proj.core
  (:require [my-proj.cfg :as cfg]))

(defn usage []
  (println "USAGE: ")
  (println "    lein run <in_path> [options]\n")
  (System/exit 0))

you can merge a config file at any point.

(cfg/merge-opts! {:cat-names ["sooty" "bilbo"]})

parse-cli-args! does all the hard work.

(defn -main [& args]
  (let [[in_path & more?] (try (cfg/parse-cli-args! args)
                            (catch IllegalArgumentException e (do (println e) (usage))))]
    (when (or more? (not in_path))
    (println "taking data from:"         in_path)
    (println "my dictionary is here:"    (cfg/opt :data-paths :dictionary))
    (println "numer of cats being used:" (cfg/opt :num-cats))
    (println "using catnip:"             (true? (cfg/opt :use-catnip)))
    (println "relevant names:"           (cfg/opt :cat-names))))

Sample output:

(-main "-n" "path/to/data" "-:cat-names" "rex,fido,rover" "--cats" "503472")
stdout=> taking data from: path/to/data
         my dictionary is here: /usr/share/dict/words
         numer of cats being used: 503472
         using catnip: true
         relevant names: [muggins felix sooty bilbo rex fido rover]
(-main "-f" "undefined alias")
stdout=> java.lang.IllegalArgumentException: Invalid or private option: -f
             lein run <in_path> [options]


             -n --catnip
                 Enables happy mode.
             -d --dict
                 Where the dictionary at?
             -c --cats
                 The number of cats to use.


defopt [k & args]

  defines an option. args can be any, or none, of the following:

  :default  x        Sets the inital value of the opt to value
  :private  x        If x is truthy, sets this option as private
  :bool     x        If x is truthy, sets this option as a boolean flag
  :validate fn       fn is called when an attempt to set the value of this opt is made.
                     an IllegalArgumentException is thrown if it returns a falsey value.
  :parse    fn       The return value of (fn x) is used as this opt's value, 
                     where x is a string given at the command line.
  :merge    fn       The return value of (fn old new) is used as this opt's value.
  :aliases  [& strs] Each str becomes an alias which, when prefixed with -, can be
                     used to set this opt at the command line.
  :help-string s     When :aliases is also set, this is printed when `print-help` is invoked.

defopts [k & args]

  defines an option container. args should be a list of `defopt` or `defopts` calls

delopt! [& ks]

  deletes the option at ks

opt [& ks]

  gets the option at ks. Throws IllegalArgumentException if it doesn't exist.

opta [alias]

  gets the option with the given alias. Throws IllegalArgumentException if it doesn't exist.

parse-cli-args! [args] [args keyfn]

  parses options from the command line. keyfn is used to process options passed as key-paths.
  i.e. [-:some:value blah] with keyfn identity results in {"some" {"value" "blah"}}. The
  default keyfn is clojure.core/keyword.

  Unused args are returned. Throws IllegalArgumentException if anything goes wrong, including:
    - failed validation
    - trying to set a private opt
    - trying to set a non-existent opt

merge-opts! [m] [ks m]

Merges option map with the given m, presumably from a trusted source

merge-public-opts! [m] [ks m]

  Merges option map with the given one, disallowing modification of private options

merge-unparsed-opts! [m] [ks m]

  Merges option map with the given one, parsing options first, and disallowing modification of private options"

set-opt! [ks v]

  Sets the option at ks to v

print-help []

  Call without arguments. Prints the set of options which have both help strings and cli aliases


  • Atomic merges
  • Allow other expressions inside defopts
  • Change :help-string to :help
  • Option 'types' e.g. flag, int, uint, nint, doubles, csv, custom.
  • Throw exceptions for invalid defopt args incl. alias re-use.
  • More subtle control over args parsing, e.g. take-while, take-n.


Copyright © 2013 David Sheldrick

Distributed under the Eclipse Public License, the same as Clojure.

Something went wrong with that request. Please try again.