Haskell Core LibrariesSource codeParentContentsIndex
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 GetOpt data structures, here's the command-line options for a (very simple) compiler:

    module Opts where
    
    import GetOpt
    import 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) -> failIO (concat errs ++ usageInfo header options)
      where header = \"Usage: ic [OPTION...] files...\"
Produced by Haddock version 0.3