System.Console.GetOpt

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System.Console.GetOpt |
Portability | portable
Stability | experimental
Maintainer | libraries@haskell.org
Contents
GetOpt Example
Description
This library provides facilities for parsing the command-line options in a standalone program. It is essentially a Haskell port of the GNU `getopt` library.
Synopsis
getOpt :: ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String])
usageInfo :: String -> [OptDescr a] -> String
data ArgOrder a
= RequireOrder
| Permute
| ReturnInOrder (String -> a)
data OptDescr a = Option [Char] [String] (ArgDescr a) String
data ArgDescr a
= NoArg a
| ReqArg (String -> a) String
| OptArg (Maybe String -> a) String
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..."
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