HsShellScript.GetOpt

GetOpt

getOpt :: ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String])

Process the command-line, and return the list of values that matched (and those that didn't). The arguments are:

• The order requirements (see ArgOrder)
• The option descriptions (see OptDescr)
• The actual command line arguments (presumably got from getArgs).

getOpt returns a triple, consisting of the argument values, a list of options that didn't match, and a list of error messages.

usageInfo :: String -> [OptDescr a] -> String

Return a string describing the usage of a command, derived from the header (first argument) and the options described by the second argument.

data ArgOrder a

What to do with options following non-options

Constructors

RequireOrder

no option processing after first non-option

Permute

freely intersperse options and non-options

ReturnInOrder (String -> a)

wrap non-options into options

data OptDescr a

Each OptDescr describes a single option.

The arguments to Option are:

• list of short option characters
• list of long option strings (without "--")
• argument descriptor
• explanation of option for user

Constructors

Option [Char] [String] (ArgDescr a) String

data ArgDescr a

Describes whether an option takes an argument or not, and if so how the argument is injected into a value of type a.

Constructors

NoArg a

no argument expected

ReqArg (String -> a) String

option requires argument

OptArg (Maybe String -> a) String

optional argument

Example

To hopefully illuminate the role of the different data structures, here's the command-line options for a (very simple) compiler:

   module Opts where
   
   import System.Console.GetOpt
   import Data.Maybe ( fromMaybe )
   
   data Flag 
    = Verbose  | Version 
    | Input String | Output String | LibDir String
   	deriving Show
   
   options :: [OptDescr Flag]
   options =
    [ Option ['v']     ["verbose"] (NoArg Verbose)       "chatty output on stderr"
    , Option ['V','?'] ["version"] (NoArg Version)       "show version number"
    , Option ['o']     ["output"]  (OptArg outp "FILE")  "output FILE"
    , Option ['c']     []          (OptArg inp  "FILE")  "input FILE"
    , Option ['L']     ["libdir"]  (ReqArg LibDir "DIR") "library directory"
    ]
   
   inp,outp :: Maybe String -> Flag
   outp = Output . fromMaybe "stdout"
   inp  = Input  . fromMaybe "stdout"
   
   compilerOpts :: [String] -> IO ([Flag], [String])
   compilerOpts argv = 
   	case (getOpt Permute options argv) of
   	   (o,n,[]  ) -> return (o,n)
   	   (_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
     where header = "Usage: ic [OPTION...] files..."