chickadee » args

Args

args provides command-line argument handling, implemented on top of SRFI 37's args-fold.

Documentation

This extension provides a wrapper around SRFI 37 (args-fold). The main goal is to let the user parse command-line arguments without having to write a lot of similar support code every time.

By default, options and operands (non-options) are collected into two lists and returned by the parser, and unrecognized options complain and display help. Therefore, it is very possible not to write any option-procs, operand-procs, or unrecognized-procs as required by SRFI 37. However, the capability to customize is there should you need it.

Additionally, the help text for your options can be generated for you, so your options and usage information don't get out of sync.

Creating options

(args:make-option (OPTION-NAME ...) ARG-DATA DOCSTRING [BODY])syntax

Make an args:option record, suitable for passing to args:parse.

OPTION-NAME ... is a sequence of short or long option names. They must be literal symbols; single-character symbols become short options, and longer symbols become long options. So (args:make-option (c cookie) ...) specifies a short option -c and long option --cookie. Under the hood, (c cookie) becomes '(#\c "cookie"), as expected by SRFI 37's OPTION.

ARG-DATA is either a pair (ARG-TYPE ARG-NAME) or a plain keyword ARG-TYPE. ARG-TYPE is a keyword that specifies whether the option takes an argument:

#:requiredArgument is required
#:optionalArgument is optional
#:noneNo argument (actually, any other value than #:required or #:optional is interpreted as #:none)

ARG-NAME, if provided, is a string specifying the name of the argument. This name is used in the help text produced by args:usage.

DOCSTRING is the help text.

BODY is an optional sequence of statements executed when this option is encountered. BODY is an option-processor as defined in SRFI 37, and has access to the variables OPT (the current #<option>), NAME (the option name) and ARG (argument value).

Behind the scenes, BODY is wrapped in code which adds the current option NAME and its argument ARG to the final options alist. So, simply leave BODY blank and options will be collected for you.

When the option takes no argument (is of type #:none) then ARG is #t, turning it into a boolean. On the other hand, when the option takes an optional argument that is omitted, then ARG is #f; so to set a default of foo, one may say in the body:

(set! arg (or arg "foo"))

Parsing the command line

args:parse ARGS OPTIONS-LIST #!optional OPTIONALSprocedure

Parse ARGS, a list of command-line arguments given as strings, and return two values: an alist of option names (symbols) and their values, and a list of operands (non-option arguments).

Operands are returned in order, but options are returned in reverse order. Duplicate options are retained in the options alist, so this lets assq find the last occurrence of any duplicate option on the command line. A (name . value) pair is added for each alias of every option found, so any alias is a valid lookup key.

OPTIONS-LIST is a list of accepted options, each created by args:make-option.

OPTIONALS is an optional sequence of keywords and values:

#:operand-proc PROCcalls PROC for each operand, with arguments OPERAND OPTIONS OPERANDS. PROC must return the next seeds, (values OPTIONS OPERANDS).
#:unrecognized-proc PROCcalls PROC for each unrecognized option, with arguments OPTION NAME ARG OPTIONS OPERANDS

The default operand-proc is a no-op, and the default unrecognized-proc issues an error message and calls the help option's processor. See the args-fold documentation for usage information and an explanation of the procedure arguments; OPTIONS and OPERANDS are seed values.

(args:help-options [default: ("help" #\h #\?)])parameter

List of option names (strings or single characters, as in SRFI 37) to be considered 'help' options, in order of preference. args:parse uses this to select a help option from the option list it is passed. This is currently used only for unrecognized options, for which the help option is automatically invoked.

Usage information

Well-behaved programs display help or usage text when invoked with an option such as --help. args:usage will generate a formatted list of options in the GNU style, from a list of args:options. Around this you might place a descriptive header and footer.

args:usage OPTION-LISTprocedure

Generate a formatted list of options from OPTION-LIST, and return a string suitable for embedding into help text. The single string consists of multiple lines, with a newline at the end of each line. Thus, a typical use would be (print (args:usage opts)).

(args:width [default: 25])parameter

Width of the left (option) column. We don't automatically format this column based on the length of the longest option, but you can set its width manually.

The formatter maintains at least 2 spaces between the option keys and the option docstrings. If there is not enough space, the docstring will start on the next line. The 2 spaces of padding are included in args:width. The indent does not get counted in args:width. So the docstrings always begin at column args:indent + args:width.

(args:separator [default: ", "])parameter

The string separator inserted between multiple options on the same line.

(args:indent [default: 1])parameter

Number of spaces to indent the options from the left. This is not considered to be part of `args:width`.

Operands and unrecognized options (advanced)

These are suitable for use with #:operand-proc or #:unrecognized-proc in args:parse. Most users will probably not customize these procedures themselves, but a couple useful prefabricated ones are provided.

args:ignore-unrecognized-optionsprocedure

Silently ignore unrecognized options, and omit from the options alist.

args:accept-unrecognized-optionsprocedure

Silently add unrecognized options to the options alist.

Examples

(use args)
;;; Note that missing required args can only be detected if their option appears last,
;;; and optional args must not be separated from their option by a space
;;; (e.g. -d2 or --debug=2, not -d 2 or --debug 2).

(define opts
 (list (args:make-option (c cookie)    #:none     "give me cookie"
         (print "cookie was tasty"))
       (args:make-option (d)           (optional: "LEVEL")  "debug level [default: 1]"
         (set! arg (string->number (or arg "1"))))
       (args:make-option (e elephant)  #:required "flatten the argument"
         (print "elephant: arg is " arg))
       (args:make-option (f file)      (required: "NAME")   "parse file NAME")
       (args:make-option (l really-long-option-name) (required: "NAME")
                         "very long option NAME to show wrapping")
       (args:make-option (v V version) #:none     "Display version"
         (print "args-example $Revision: 1.3 $")
         (exit))
       (args:make-option (abc)         #:none     "Recite the alphabet")
       (args:make-option (h help)      #:none     "Display this text"
         (usage))))

(define (usage)
 (with-output-to-port (current-error-port)
   (lambda ()
     (print "Usage: " (car (argv)) " [options...] [files...]")
     (newline)
     (print (args:usage opts))
     (print "Report bugs to zbigniewsz at gmail.")))
 (exit 1))

(receive (options operands)
    (args:parse (command-line-arguments) opts)
  (print "-e -> " (alist-ref 'elephant options))) ;; 'e or 'elephant both work

If command line is --cookie -e test -e hello:

  cookie was tasty
  elephant: arg is test
  elephant: arg is hello
  -e -> hello

If command line is --cookie -e test --foo:

cookie was tasty
elephant: arg is test
./args-example: unrecognized option: foo
Usage: ./args-example [options...] [files...]

 -c, --cookie             give me cookie
 -d [LEVEL]               debug level [default: 1]
 -e, --elephant=ARG       flatten the argument
 -f, --file=NAME          parse file NAME
 -l, --really-long-option-name=NAME
                          very long option NAME to show wrapping
 -v, -V, --version        Display version
     --abc                Recite the alphabet
 -h, --help               Display this text

Report bugs to zbigniewsz at gmail.

Using indent 5, width 35 and a single space for the separator:

#;> (print (parameterize ((args:separator " ")
                          (args:indent 5)
                          (args:width 35))
             (args:usage opts)))

     -c --cookie                        give me cookie
     -d --debug[=LEVEL]                 debug level [default: 1]
     -e --elephant=ARG                  flatten the argument
     -f --file=NAME                     parse file NAME
     -l --really-long-option-name=NAME  really long option NAME to show wrapping
     -v -V --version                    Display version
        --abc                           Recite the alphabet
     -h --help                          Display this text

Additional examples can be found in args-examples.scm in the egg.

Bugs

The name args:make-option is verbose.

About this egg

Author

Jim Ursetto

Repository

This egg is hosted on the CHICKEN Subversion repository.

If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.

Version history

1.6.2
Ensure option wrapping works properly when indent != 1
1.6.1
Wrap long options at args:width instead of truncating (@tkurtbond)
1.6.0
Ported to CHICKEN 5 [Kooda]
1.5.1
Bugfix for 1.5.0 -- ensure option body sees transformed #t arg value
1.5.0
#:optional args return a #t instead of #f value (suggested by Matt Gushee and Peter Bex)
1.4.4
Allow use of make-option inside hygienic macros
1.4.3
Use (program-name) to ensure correct $0 in scripts (zb; noticed by hypnocat)
1.4.2
Accept numerical args, drop args:make-operand-proc (zb)
1.4
Ported to Chicken 4 [Ivan Raikov]
1.3
check for presence of required option arguments [Ivan Raikov]
1.2
commify tail-recursive (Ivan Shmakov); add args:separator, args:indent (zb)
1.1
Fix exports (Felix, Kon)
1.0
Initial release

Requirements

srfi-37

License

Copyright (c) 2005-2021 Jim Ursetto.  All rights reserved.

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