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Compact [sub]command line parsing library, for Clojure. Perfect for scripting (who said Clojure is not good for scripting?).

Especially when scripting, you should write interesting code, not boilerplate. Command line apps are usually so tiny that there is absolutely no reason why your code should not be self-documenting. Things like generating help text and parsing command flags/options should not hinder productivity when writing a command line app.

CLI-matic works with GraalVM, giving unbeatable performance for stand-alone command-line apps that do not even need a Java installation - see Command-line apps with Clojure and GraalVM: 300x better start-up times.


The library is available on Clojars:

Clojars Project

Or the library can be easily referenced through Github:

  {:git/url ""
   :sha "b27bc676a879542b4e83f1bef3b9776e600018e3"}}}


  • Create all-in-one scripts with subcommands and help, in a way more compact than the excellent - but lower level - tools.cli.
  • Avoid common pre-processing. Parsing dates, integers, reading small files, downloading a JSON URL.... it should just happen. The more you declare, the less time you waste.
  • Validate with Spec. Modern Clojure uses Spec, so validation should be spec-based as well. Validation should happen at the parameter level, and across all parameters of the subcommand at once, and emit sane error messages. Again, the more you have in declarative code, the less room for mistakes.
  • Read environment variables. Passing environment variables is a handy way to inject passwords, etc. This should just happen and be declarative.
  • Capture unnamed parameters as if they were named parameters, with casting, validation, etc.

While targeted at scripting, CLI-matic of course works with any program receiving CLI arguments.


Say we want to create a short script, in Clojure, where we want to run a very simple calculator that either sums A to B or subtracts B from A:

$ clj -m calc add -a 40 -b 2
$ clj -m calc sub -a 10 -b 2
$ clj -m calc --base 16 add -a 30 -b 2

We also want it to display its help:

$clj -m calc -?
 toycalc - A command-line toy calculator

 toycalc [global-options] command [command options] [arguments...]


   add, a   Adds two numbers together
   sub, s   Subtracts parameter B from A

       --base N  10  The number base for output
   -?, --help

And help for sub-commands:

$clj -m calc add -?
 toycalc add - Adds two numbers together

 toycalc [add|a] [command options] [arguments...]

   -a, --a1 N  0  Addendum 1
   -b, --a2 N  0  Addendum 2
   -?, --help

But while we are coding this, we do not realy want to waste time writing any parsing logic. What we care about implementing are the functions add-numbers and sub-numbers where we do actual work; the rest should be declared externally and/or "just happen".

From the point of view of us programmers, we'd like to have a couple of functions like:

(defn add-number
	"Sums A and B together, and prints it in base `base`"
	[{:keys [a b base]}]
	(Integer/toString (+ a b) base))

And nothing more; the fact that both parameters exist, are of the right type, have the right defaults, print the correct help screen, etc., should ideally not be a concern.

So we define a configuration:

  {:app         {:command     "toycalc"
                 :description "A command-line toy calculator"
                 :version     "0.0.1"}

   :global-opts [{:option  "base"
                  :as      "The number base for output"
                  :type    :int
                  :default 10}]

   :commands    [{:command     "add"
                  :description "Adds two numbers together"
                  :opts        [{:option "a" :as "Addendum 1" :type :int}
                                {:option "b" :as "Addendum 2" :type :int :default 0}]              
                  :runs        add_numbers}

                 {:command     "sub"
                  :description "Subtracts parameter B from A"
                  :opts        [{:option "a" :as "Parameter A" :type :int :default 0}
                                {:option "b" :as "Parameter B" :type :int :default 0}]
                  :runs        subtract_numbers}

It contains:

  • Information on the app itself (name, version)
  • The list of global parameters, i.e. the ones that apply to al subcommands (may be empty)
  • A list of sub-commands, each with its own parameters in :opts, and a function to be called in :runs. You can optionally validate the full parameter-map that is received by subcommand at once by passing a Spec into :spec.
  • If within the subcommand you add a 0-arity function to :on-shutdown, it will be called when the JVM terminates. This is mostly useful for long running servers, or to do some clean-up. Note that the hook is always called - whether the shutdown is forced by pressing (say) Ctrl+C or just by the JVM exiting. See the examples.

And...that's it!

Current pre-sets

The following pre-sets (:type) are available:

  • :int - an integer number
  • :int-0 - an integer number, with defaults to zero
  • :float - a float number
  • :float-0 - a float number, with defaults to zero
  • :string - a string
  • :keyword - a string representation of a keyword, leading colon is optional, if no namespace is specified. ::foo will be converted to :user/foo, otherwise it will work as expected.
  • :json - a JSON literal value, that will be decoded and returned as a Clojure structure.
  • :yaml - a YAML literal value, that will be decoded and returned as a Clojure structure.
  • :edn - an EDN literal value, that will be decoded and returned.
  • :yyyy-mm-dd - a Date object, expressed as "yyyy-mm-dd" in the local time zone
  • :slurp - Receives a file name - reads is as text and returns it as a single string. Handles URIs correctly.
  • :slurplines - Receives a file name - reads is as text and returns it as a seq of strings. Handles URIs correctly.
  • :ednfile - a file (or URL) containing EDN, that will be decoded and returned as a Clojure structure.
  • :jsonfile - a file (or URL) containing JSON, that will be decoded and returned as a Clojure structure.
  • :yamlfile - a file (or URL) containing YAML, that will be decoded and returned as a Clojure structure.

For all options, you can then add:

  • :default the default value, as expected after conversion. If no default, the value will be passed only if present. If you set :default :present this means that CLI-matic will abort if that option is not present (and it appears with a trailing asterisk in the help)
  • :multiple if true, the values for all options with the same name are stored in an array
  • :short: a shortened name for the command (if a string), or a positional argument if integer (see below).
  • :env if set, the default is read from the current value of an env variable you specify. For capture to happen, either the option must be missing, or its value must be invalid. If an option has an :env value specified to FOO, its description in the help shows [$FOO].
  • :spec: a Spec that will be used to validate the the parameter, after any coercion/transformation.

[to be done]

  • boolean types
  • having a library of ready-made types that cover most cases

Return values

The function called can return an integer; if it does, it is used as an exit code for the shell process.

Errors and exceptions return an exit code of -1; while normal executions (including invocations of help) return 0.

Positional arguments

If there are values that are not options in your command line, CLI-matic will usually return them in an array of unparsed entries, as strings. But - if you use the positional syntax for short:

{:option "a1" :short 0 :as "First addendum" :type :int :default 23}

You 'bind' the option 'a1' to the first unparsed element; this means that you can apply all presets/defaults/validation rules as if it was a named option.

So you could call your script as:

clj -m calc add --a2 3 5

And CLI-matic would set 'a2' to 3 and have "5" as an unparsed argument; and then bind it to "a1", so it will be cast to an integer. You function will be called with:

{:a1 5, :a2 3}

That is what you wanted from the start.

At the same time, the named option remains, so you can use either version. Bound entries are not removed from the unparsed command line entries.

Validation with Spec (and Expound)

CLI-matic can optionally validate any parameter, and the set of parameters you use to call the subcommand function, with Spec, and uses the excellent Expound to produce sane error messages. An example is under examples as toycalc-spec.clj - see

By using and including Expound as a depencency, you can add error descriptions where the raw Spec would be hard to read, and use a nice set of pre-built specs with readable descriptions that come with Expound - see

Help text generation

CLI-matic comes with pre-packaged help text generators for global and sub-command help. These generators can be overridden by supplying one or more of your own functions in the :app section of the configuration:

(defn my-command-help [setup]
  " ... ")

(defn gen-sub-command-help [setup subcmd]
  " ... ")

{:app {:global-help my-command-help
       :subcmd-help gen-sub-command-help}}

The function specified for :global-help accepts the CLI configuration, and :subcmd-help additionally accepts the sub-command it was called with. Each function returns a string that CLI-matic prints verbatim to the user as the full help text.

Transitive dependencies

CLI-matic currently depends on:

  • org.clojure/clojure
  • org.clojure/spec.alpha
  • org.clojure/tools.cli
  • expound

Optional dependencies

To use JSON decoding, you need Cheshire cheshire/cheshire to be on the classpath; otherwise it will break. If you do not need JSON parsing, you can do without.

To use Yaml decoding, you need io.forward/yaml on your classpath; otherwise it will break. If you do not need YAML parsing, you can do without. Note that the YAML library has reflection in it, and so is incompatible with GraalVM native images.

If Orchestra orchestra is present on the classpath, loading most namespaces triggers an instrumentation. As we already have Expound, we get easy-to-read messages for free.

Tips & tricks

Reducing startup time with skip-macros

If you run your script with the property clojure.spec.skip-macros=true you get significant savings:

	time clj -J-Dclojure.spec.skip-macros=true -m recap sv
	real	0m2.587s - user	0m6.997 - sys	0m0.332s

Versus the default:

	time clj -J-Dclojure.spec.skip-macros=false -m recap sv
	real	0m3.141s -user	0m8.707s -sys	0m0.391s

So that's like half a second for free on my machine.

Capturing current version

If you would like to capture the build environment at compile time (e.g. the exact GIT revision, or when/where the program was built, or the version of your project as defined in project.clj) so you can print meaningful version numbers without manual intervention, you may want to include and use it to provide everything to you.


The use and distribution terms for this software are covered by the Eclipse Public License 1.0 ( which can be found in the file epl.html at the root of this distribution. By using this software in any fashion, you are agreeing to be bound by the terms of this license.

You must not remove this notice, or any other, from this software.

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