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Command-line option parsing.

  1. Outdated egg!
  2. getopt-long
    1. Description
    2. Command-line option grammar
    3. Library Procedures
    4. Examples
    5. Version History
    6. License


The getopt-long library implements command line option parsing, in the spirit of the GNU C library function getopt_long. Both long and short options are supported.

The theory is that people should be able to constrain the set of options they want to process using a grammar, rather than some arbitrary structure. The grammar makes the option descriptions easy to read.

Command-line option grammar

The option grammar is an s-expression of the form:

              (PROPERTY VALUE) ...) 

Each OPTION-NAME should be a symbol. Given this grammar, getopt-long will then accept a command-line option named --OPTION-NAME.

If [DOCSTRING] is provided, it must be a string containing a brief description of the option.

Each option can have the following (PROPERTY VALUE) pairs:

(single-char CHAR)
Accept -CHAR as a single-character equivalent to --OPTION. This is how to specify traditional Unix-style flags.
(required BOOL)
If BOOL is true, the option is required. getopt-long will raise an error if it is not found in the list of arguments.
(value FLAG)
If FLAG is #t, the option requires a value; if it is #f, it does not.
(value (REQUIRED "name") [(PROPERTY VALUE) ...])
the option requires a value and the name is used by the usage procedure.
(value (OPTIONAL "name") [(PROPERTY VALUE) ...])
the option may appear with or without a named value.

In addition, the following properties can be defined for a value:

(predicate FUNC)
If the option accepts a value (i.e. you specified (REQUIRED ...) or (OPTIONAL ...) for this option), then getopt-long will apply FUNC to the value, and throw an exception if the result is #f. FUNC should be a procedure which accepts a string and returns a boolean value; you may need to use quasiquotes to get it into the grammar.
(transformer FUNC)
If the option accepts a value, then getopt will apply FUNC to the string provided on the command line, and put the resulting value in the list of parsed options returned by getopt-long.

The (PROPERTY VALUE) pairs may occur in any order, but each property may occur only once. By default, options do not have single-character equivalents, are not required, and do not take values.

Library Procedures

getopt-long is a procedure for parsing command-line arguments in a manner consistent with GNU programs.

usage is a procedure that creates help strings given a grammar for the command-line arguments.


Parse the arguments ARGS according to the argument list grammar GRAMMAR.

ARGS should be a list of strings. Its first element should be the name of the program; subsequent elements should be the arguments that were passed to the program on the command line. The program-arguments procedure returns a list of this form.

In ARGS, single-character options may be combined, in the usual Unix fashion: ("-x" "-y") is equivalent to ("-xy"). If an option accepts values, then it must be the last option in the combination; the value is the next argument. So, for example, using the following grammar:

    ((apples    (single-char #\a))
     (blimps    (single-char #\b) (value #t))
     (catalexis (single-char #\c) (value #t)))

the following argument lists would be acceptable:

  ("-a" "-b" "bang" "-c" "couth")     ("bang" and "couth" are the values
                                       for "blimps" and "catalexis")
  ("-ab" "bang" "-c" "couth")         (same)
  ("-ac" "couth" "-b" "bang")         (same)
  ("-abc" "couth" "bang")             (an error, since `-b' is not the
                                       last option in its combination)

If an option's value is optional, then getopt-long decides whether it has a value by looking at what follows it in ARGS. If the next element is does not appear to be an option itself, then that element is the option's value.

The value of a long option can can only follow the option name, separated by an `=' character.

If the option "--" appears in ARGS, argument parsing stops there; subsequent arguments are returned as ordinary arguments, even if they resemble options. So, in the argument list:

       ("--apples" "Granny Smith" "--" "--blimps" "Goodyear")

getopt-long will recognize the `apples' option as having the value "Granny Smith", but it will not recognize the `blimp' option; it will return the strings "--blimps" and "Goodyear" as ordinary argument strings.

The getopt-long function returns an association list in which the key is an option name --- one of the symbols from GRAMMAR --- and each key is associated either with a single value (if the named option has been given once), or with a list of values (if the option was given multiple times). Options that were not given are not present.

There is a special item in the returned alist with a key '@: this is the list of arguments that are not options or option values.

Optional keyword argument UNKNOWN-OPTION-HANDLER is a procedure that receives as an argument a list of all options that were given as input but were unrecognized by the grammar. The default unknown option handler raises an error.

Optional keyword argument LONG-OPTION-VALUE-CSET is a SRFI-14 character set that specifies all valid characters in an option value. This argument defaults to:

 (char-set-union char-set:letter+digit 
                  (char-set #\_ #\^ #\$ #\= #\space))

By default, getopt-long throws an exception if:


 (define grammar
  `((lockfile-dir "location of the lock file"   ; <-- example for docstring
                  (required #t)
                  (value #t)
                  (single-char #\k)
                  (value (required DIR)
                         (predicate ,directory?)))
    (verbose (required #f)
             (single-char #\v)
             (value #f))
    (x-includes (single-char #\x)
             (value #t))
    (rnet-server (single-char #\y)
                 (value (required SERVER)
                 (predicate ,string?)))
  (getopt-long '("my-prog" "-vk" "/tmp" "foo1" "--x-includes=/usr/include"
                 "--rnet-server=lamprod" "--" "-fred" "foo2" "foo3")

Version History


The getopt-long library was written by Thien-Thi Nguyen for Guile Scheme.

getopt-long was ported to Chicken Scheme by Ivan Raikov.

Copyright (C) 1998, 2001, 2006 Free Software Foundation,

This program is free software: you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License
as published by the Free Software Foundation, either version 3 of
the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
General Public License for more details.

A full copy of the Lesser GPL license can be found at