7.4.4 Reference Documentation for getopt-long

Scheme Procedure: getopt-long args grammar

Parse the command line given in args (which must be a list of strings) according to the option specification grammar.

The grammar argument is expected to be a list of this form:

((option (property value) …) …)

where each option is a symbol denoting the long option, but without the two leading dashes (e.g. version if the option is called --version).

For each option, there may be list of arbitrarily many property/value pairs. The order of the pairs is not important, but every property may only appear once in the property list. The following table lists the possible properties:

(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 args.

(value bool)

If bool is #t, the option accepts a value; if it is #f, it does not; and if it is the symbol optional, the option may appear in args with or without a value.

(predicate func)

If the option accepts a value (i.e. you specified (value #t) for this option), then getopt-long will apply func to the value, and throw an exception if it returns #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 grammar.

getopt-long’s args parameter is expected to be a list of strings like the one returned by command-line, with the first element being the name of the command. Therefore getopt-long ignores the first element in args and starts argument interpretation with the second element.

getopt-long signals an error if any of the following conditions hold.

• The option grammar has an invalid syntax.
• One of the options in the argument list was not specified by the grammar.
• A required option is omitted.
• An option which requires an argument did not get one.
• An option that doesn’t accept an argument does get one (this can only happen using the long option --opt=value syntax).
• An option predicate fails.