A wrapper around net.didierverna.clon which makes command line arguments parsing easier.

Upstream URL


Alexander Artemenko



DEFMAIN - intuitive command line options parser for Common Lisp

DEFMAIN ASDF System Details



Library net.didierverna.clon very powerful, but too complicated to use in simple cases. This library provides a wrapper which will suite your needs in 80% cases.

Compare this code, which uses defmain macro:

(defmain (main) ((debug "Show traceback instead of short message."
                        :flag t)
                 (log   "Filename to write log to.")
                 (token "GitHub personal access token."
                        :env-var "TOKEN")
                 &rest repositories)
  "Utility to analyze github forks."

   ;; Making real work
  (loop for reporitory in repositories
        do (analyze repository
                    :log log
                    :debug debug
                    :token token)))

With code providing the same functionality, but using raw net.didierverna.clon system:

(net.didierverna.clon:defsynopsis (:postfix "REPOSITORY")
  (text :contents "This utility builds a report about all non-merged commits for any github repository. Just give some repository name like \"antirez/redis\" as an argument and pipe stdout to some file.")
  (flag :short-name "h" :long-name "help"
        :description "Print this help and exit.")
  (flag :short-name "v" :long-name "version"
        :description "Print version number and exit.")
  (flag :long-name "debug"
        :description "Show traceback instead of short message.")
  (stropt :short-name "l" :long-name "log"
          :description "Filename to write log to.")
  (stropt :short-name "t" :long-name "token"
          :env-var "TOKEN"
          :description "GitHub personal access token."))

(defun main (&rest argv)
  (declare (ignorable argv))
  (net.didierverna.clon:make-context :cmdline (cons "12forks" argv))
  (when (net.didierverna.clon:getopt :long-name "help")

  ;; Making real work
  (loop for reporitory in (remainder)
        do (analyze repository
                    :log (net.didierverna.clon:getopt :long-name "log")
                    :debug (net.didierverna.clon:getopt :long-name "debug")
                    :token (net.didierverna.clon:getopt :long-name "token"))))


This system is available as part of the distribution. Follow instruction on the site to setup the distribution, and then install defmain system using Quicklisp client:

(ql:quickload :defmain)


The main entry point for defining the main function for your program is the defmain macro:

macro defmain:defmain (name &key program-name) (&rest args) &body body

This macro let you to define a main function for a command-line program.

Usually the NAME argument will be just MAIN. This name will be bound to a function which will process arguments and execute the BODY.

ARGS should contain an arguments definition. Each definition is a list of the form:


Argument's NAME should be a symbol. It names a variable which will be bound during the BODY execution. Also, this name is lowercased and used to form a --long command line argument.

The lowercased first letter of the NAME is used as a short version of the argument, like -l. But sometimes you might encounter duplication errors when having a few arguments starting from the same letter. In this case provide SHORT option, to override the letter, used for the short option.

For example, here we have a conflict:

(defmain (main) ((version "Print program version and exit")
                 (verbose "Provide more detail on the output"))

But we can tell defmain (1 2) to use -V option for verbose, instead of -v

(defmain (main) ((version "Print program version and exit")
                 (verbose "Provide more detail on the output" :short "V"))

Also, we can pass NIL, to turn off short version for VERBOSE argument:

(defmain (main) ((version "Print program version and exit")
                 (verbose "Provide more detail on the output" :short NIL))

If some of your options are boolean, then give it a :FLAG t option, and a variable will become T if user provided this flag on the command-line.

Also, you might want to specify a DEFAULT value for the argument or provide an environment variable name using ENV-VAR. The value will be take from the environment variable unless it was provided by the user on the command-line.

Arguments list of defmain macro might end with &REST SOME-VAR. In this case, all unprocessed command line arguments will be collected into the SOME-VAR list.

By default program name, shown in the --help, will be the same as the name of the function or taken as a third part of the ROS.SCRIPT.THIRD-PART package name, if you are using Roswell. However, you can override it providing the PROGRAM-NAME argument.


Also, you might want to build a more complex command-line interface with subcommands.

In this case, you need to use defmain macro to define the main entry-point, and then to define additional subcommands using defcommand macro:

macro defmain:defcommand (parent name) (&rest args) &body body

This macro is similar to defmain macro in terms of arguments and body processing.

The only difference is that instead of the single name you have to provide a list of two names:

  • First element should be the name of the parent function. It can be either a main entry-point or other subcommand.

  • Second element is a symbol to name the subcommand.

Here is an example with of a program with two subcommands. Pay attention to the MAIN function's argument list. It ends with a special symbol &SUBCOMMAND. It should be provided to let macro know there will be some subcommands defined later.

(defmain (main) ((verbose "More detail in the output")

(defcommand (main upload) ((upstream "Repository name")
                           (force "Rewrite changes in case of conflict"
                                  :flag t))

(defcommand (main sync) ()
  "Yet another subcommand."

All arguments, specified for the MAIN function also bound for all it's subcommands. On command-line these arguments should preceed the subcommand's name

By default, main command run's specified subcommand and exits, but you can use it as a decorator, to execute some common code before and after as subcommand.

To run subcommand, execute subcommand function:

(defmain (main) ((verbose "More detail in the output"))
  (format t "Before subcommand.~%")
  (format t "After subcommand.~%"))


When writing more complex logic, these helpers could be useful:

function defmain:print-help

Outputs to stdout a help about command line utility.

function defmain:print-commands-help

Outputs information about supported subcommands.

It should be called from the function defined with defmain macro.

function defmain:get-subcommand-name

Returns a string with current subcommand's name.

It should be called from the function defined with defmain macro.

function defmain:subcommand

Executes the current subcommand. It is called automatically at the end of the main body unless you call it manually.

It can be called from the function defined with defmain macro.


  • Make better support for integer arguments.

  • Support more types of arguments, like filepathes and enums.

  • Raise error when two short options are identical during macro-expansion, not during runtime. Right now the clon checks this during runtime:

Unhandled SIMPLE-ERROR in thread #<SB-THREAD:THREAD "main thread"
RUNNING {10005285B3}>:

Options #<LISPOBJ {1002705593}> and #<STROPT {1002705C03}>:
indentical short name "s".

Backtrace for: #<SB-THREAD:THREAD "main thread" RUNNING
~A: indentical short name ~S." {100277D8F3}> #<unused argument>
"Options ~A and ~A: indentical short name ~S." {100277D8F3}>)
2: (INVOKE-DEBUGGER #<SIMPLE-ERROR "Options ~A and ~A: indentical short name ~S." {100277D8F3}>)
3: (ERROR "Options ~A and ~A: indentical short name ~S."
#<NET.DIDIERVERNA.CLON: :STROPT {1002705C03}> "s")
#<NET.DIDIERVERNA.CLON::STROPT {1002705C03}>) [fast-method]
{100270C013}>) [fast-method]

[generated by 40ANTS-DOC]

Dependencies (11)

  • alexandria
  • ci
  • cl-clon
  • cl-hamcrest
  • cl-inflector
  • cl-strings
  • doc
  • docs-builder
  • named-readtables
  • pythonic-string-reader
  • uiop

Dependents (3)

  • GitHub
  • Quicklisp