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| System.Console.GetOpt | | Portability | portable | | Stability | experimental | | Maintainer | libraries@haskell.org |
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| 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.
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| Synopsis |
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| GetOpt
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| 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 option arguments, a list
of non-options, and a list of error messages.
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| getOpt' :: ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String], [String]) |
| This is almost the same as getOpt, but returns a quadruple
consisting of the option arguments, a list of non-options, a list of
unrecognized options, and a list of error messages.
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| 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.
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| 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
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| 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
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| 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.
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| Examples
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| To hopefully illuminate the role of the different data structures,
here are the command-line options for a (very simple) compiler,
done in two different ways.
The difference arises because the type of getOpt is
parameterized by the type of values derived from flags.
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| Interpreting flags as concrete values
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A simple choice for the type associated with flags is to define a type
Flag as an algebraic type representing the possible flags and their
arguments:
module Opts1 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 "stdin"
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..."
Then the rest of the program will use the constructed list of flags
to determine it's behaviour.
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| Interpreting flags as transformations of an options record
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A different approach is to group the option values in a record of type
Options, and have each flag yield a function of type
Options -> Options transforming this record.
module Opts2 where
import System.Console.GetOpt
import Data.Maybe ( fromMaybe )
data Options = Options
{ optVerbose :: Bool
, optShowVersion :: Bool
, optOutput :: Maybe FilePath
, optInput :: Maybe FilePath
, optLibDirs :: [FilePath]
} deriving Show
defaultOptions = Options
{ optVerbose = False
, optShowVersion = False
, optOutput = Nothing
, optInput = Nothing
, optLibDirs = []
}
options :: [OptDescr (Options -> Options)]
options =
[ Option ['v'] ["verbose"]
(NoArg (\ opts -> opts { optVerbose = True }))
"chatty output on stderr"
, Option ['V','?'] ["version"]
(NoArg (\ opts -> opts { optShowVersion = True }))
"show version number"
, Option ['o'] ["output"]
(OptArg ((\ f opts -> opts { optOutput = Just f }) . fromMaybe "output")
"FILE")
"output FILE"
, Option ['c'] []
(OptArg ((\ f opts -> opts { optInput = Just f }) . fromMaybe "input")
"FILE")
"input FILE"
, Option ['L'] ["libdir"]
(ReqArg (\ d opts -> opts { optLibDirs = optLibDirs opts ++ [d] }) "DIR")
"library directory"
]
compilerOpts :: [String] -> IO (Options, [String])
compilerOpts argv =
case getOpt Permute options argv of
(o,n,[] ) -> return (foldl (flip id) defaultOptions o, n)
(_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
where header = "Usage: ic [OPTION...] files..."
Similarly, each flag could yield a monadic function transforming a record,
of type Options -> IO Options (or any other monad), allowing option
processing to perform actions of the chosen monad, e.g. printing help or
version messages, checking that file arguments exist, etc.
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| Produced by Haddock version 0.8 |
