# CmdArgs: Easy Command Line Processing [![Hackage version](https://img.shields.io/hackage/v/cmdargs.svg?style=flat)](https://hackage.haskell.org/package/cmdargs) [![Build Status](https://img.shields.io/travis/ndmitchell/cmdargs.svg?style=flat)](https://travis-ci.org/ndmitchell/cmdargs)
CmdArgs is a Haskell library for defining command line parsers. The two features that make it a better choice than the standard getopt library are:
A very simple example of a command line processor is:
data Sample = Sample {hello :: String} deriving (Show, Data, Typeable) sample = Sample{hello = def &= help "World argument" &= opt "world"} &= summary "Sample v1" main = print =<< cmdArgs sample
Despite being very concise, this processor is already fairly well featured:
$ runhaskell Sample.hs --hello=world Sample {hello = "world"} $ runhaskell Sample.hs --help Sample v1, (C) Neil Mitchell 2009 sample [FLAG] -? --help[=FORMAT] Show usage information (optional format) -V --version Show version information -v --verbose Higher verbosity -q --quiet Lower verbosity -h --hello=VALUE World argument (default=world)
The rest of this document explains how to write the "hello world" of command line processors, then how to extend it with features into a complex command line processor. Finally this document gives three samples, which the cmdargs program can run. The three samples are:
For each example you are encouraged to look at it's source (see the darcs repo, or the bottom of this document) and run it (try cmdargs hlint --help). The HLint program is fairly standard in terms of it's argument processing, and previously used the System.Console.GetOpt library. Using GetOpt required 90 lines and a reasonable amount of duplication. Using CmdArgs the code requires 30 lines, and the logic is much simpler.
Thanks to Kevin Quick for substantial patches, and additional code contributions from Sebastian Fischer and Daniel Schoepe.
The following code defines a complete command line argument processor:
{-# LANGUAGE DeriveDataTypeable #-} module Sample where import System.Console.CmdArgs data Sample = Sample {hello :: String} deriving (Show, Data, Typeable) sample = Sample{hello = def} main = print =<< cmdArgs sampleTo use the CmdArgs library there are three steps:
Now we have a reasonably functional command line argument processor. Some sample interactions are:
$ runhaskell Sample.hs --hello=world Sample {hello = "world"} $ runhaskell Sample.hs --version The sample program $ runhaskell Sample.hs --help The sample program sample [OPTIONS] -? --help Display help message -V --version Print version information -h --hello=ITEM
CmdArgs uses defaults to automatically infer a command line parser for a value, and provides annotations to override any of the the defaults. CmdArgs automatically supports --help and --version flags, and optionally supports verbosity flags.
In order to control the behaviour we can add attributes. For example to add an attribute specifying the help text for the --hello argument we can write:
sample = Sample{hello = def &= help "Who to say hello to"}
We can add additional attributes, for example to specify the type of the value expected by hello:
sample = Sample {hello = def &= help "Who to say hello to" &= typ "WORLD"}
Now when running --help the final line is:
-h --hello=WORLD Who to say hello to
There are many more attributes, detailed in the Haddock documentation.
To specify a program with multiple modes, similar to darcs, we can supply a data type with multiple constructors, for example:
data Sample = Hello {whom :: String} | Goodbye deriving (Show, Data, Typeable) hello = Hello{whom = def} goodbye = Goodbye main = print =<< cmdArgs (modes [hello,goodbye])Compared to the first example, we now have multiple constructors, and a sample value for each constructor is passed to cmdArgs. Some sample interactions with this command line are:
$ runhaskell Sample.hs hello --whom=world Hello {whom = "world"} $ runhaskell Sample.hs goodbye Goodbye $ runhaskell Sample.hs --help The sample program sample [OPTIONS] Common flags -? --help Display help message -V --version Print version information sample hello [OPTIONS] -w --whom=ITEM sample goodbye [OPTIONS]
As before, the behaviour can be customised using attributes.
For each of the following examples we first explain the purpose of the program, then give the source code, and finally the output of --help=HTML. The programs are intended to show sample uses of CmdArgs, and are available to experiment with through cmdargs progname.
The HLint program analyses a list of files, using various options to control the analysis. The command line processing is simple, but a few interesting points are:
{-# LANGUAGE DeriveDataTypeable #-} module HLint where import System.Console.CmdArgs data HLint = HLint {report :: [FilePath] ,hint :: [FilePath] ,color :: Bool ,ignore_ :: [String] ,show_ :: Bool ,extension :: [String] ,language :: [String] ,utf8 :: Bool ,encoding :: String ,find :: [FilePath] ,test_ :: Bool ,datadir :: [FilePath] ,cpp_define :: [String] ,cpp_include :: [FilePath] ,files :: [FilePath] } deriving (Data,Typeable,Show,Eq) hlint = HLint {report = def &= opt "report.html" &= typFile &= help "Generate a report in HTML" ,hint = def &= typFile &= help "Hint/ignore file to use" ,color = def &= name "c" &= name "colour" &= help "Color the output (requires ANSI terminal)" ,ignore_ = def &= typ "MESSAGE" &= help "Ignore a particular hint" ,show_ = def &= help "Show all ignored ideas" ,extension = def &= typ "EXT" &= help "File extensions to search (defaults to hs and lhs)" ,language = def &= name "X" &= typ "LANG" &= help "Language extension (Arrows, NoCPP)" ,utf8 = def &= help "Use UTF-8 text encoding" ,encoding = def &= typ "ENC" &= help "Choose the text encoding" ,find = def &= typFile &= help "Find hints in a Haskell file" ,test_ = def &= help "Run in test mode" ,datadir = def &= typDir &= help "Override the data directory" ,cpp_define = def &= typ "NAME[=VALUE]" &= help "CPP #define" ,cpp_include = def &= typDir &= help "CPP include path" ,files = def &= args &= typ "FILES/DIRS" } &= verbosity &= help "Suggest improvements to Haskell source code" &= summary "HLint v0.0.0, (C) Neil Mitchell" &= details ["Hlint gives hints on how to improve Haskell code","" ,"To check all Haskell files in 'src' and generate a report type:"," hlint src --report"] mode = cmdArgsMode hlintHLint v0.0.0, (C) Neil Mitchell hlint [OPTIONS] [FILES/DIRS] Suggest improvements to Haskell source code Common flags: -r --report[=FILE] Generate a report in HTML -h --hint=FILE Hint/ignore file to use -c --colour --color Color the output (requires ANSI terminal) -i --ignore=MESSAGE Ignore a particular hint -s --show Show all ignored ideas --extension=EXT File extensions to search (defaults to hs and lhs) -X --language=LANG Language extension (Arrows, NoCPP) -u --utf8 Use UTF-8 text encoding --encoding=ENC Choose the text encoding -f --find=FILE Find hints in a Haskell file -t --test Run in test mode -d --datadir=DIR Override the data directory --cpp-define=NAME[=VALUE] CPP #define --cpp-include=DIR CPP include path -? --help Display help message -V --version Print version information -v --verbose Loud verbosity -q --quiet Quiet verbosity Hlint gives hints on how to improve Haskell code To check all Haskell files in 'src' and generate a report type: hlint src --report
The Diffy sample is a based on the idea of creating directory listings and comparing them. The tool can operate in two separate modes, create or diff. This sample is fictional, but the ideas are drawn from a real program. A few notable features:
{-# LANGUAGE DeriveDataTypeable #-} module Diffy where import System.Console.CmdArgs data Diffy = Create {src :: Maybe FilePath, out :: FilePath} | Diff {old :: FilePath, new :: FilePath, out :: FilePath} deriving (Data,Typeable,Show,Eq) outFlags x = x &= help "Output file" &= typFile create = Create {src = def &= help "Source directory" &= typDir ,out = outFlags "ls.txt" } &= help "Create a fingerprint" diff = Diff {old = def &= typ "OLDFILE" &= argPos 0 ,new = def &= typ "NEWFILE" &= argPos 1 ,out = outFlags "diff.txt" } &= help "Perform a diff" mode = cmdArgsMode $ modes [create,diff] &= help "Create and compare differences" &= program "diffy" &= summary "Diffy v1.0"Diffy v1.0 diffy [COMMAND] ... [OPTIONS] Create and compare differences Common flags: -o --out=FILE Output file -? --help Display help message -V --version Print version information diffy create [OPTIONS] Create a fingerprint -s --src=DIR Source directory diffy diff [OPTIONS] OLDFILE NEWFILE Perform a diff
The Maker sample is based around a build system, where we can either build a project, clean the temporary files, or run a test. Some interesting features are:
{-# LANGUAGE DeriveDataTypeable #-} module Maker where import System.Console.CmdArgs data Method = Debug | Release | Profile deriving (Data,Typeable,Show,Eq) data Maker = Wipe | Test {threads :: Int, extra :: [String]} | Build {threads :: Int, method :: Method, files :: [FilePath]} deriving (Data,Typeable,Show,Eq) threadsMsg x = x &= help "Number of threads to use" &= name "j" &= typ "NUM" wipe = Wipe &= help "Clean all build objects" test_ = Test {threads = threadsMsg def ,extra = def &= typ "ANY" &= args } &= help "Run the test suite" build = Build {threads = threadsMsg def ,method = enum [Release &= help "Release build" ,Debug &= help "Debug build" ,Profile &= help "Profile build"] ,files = def &= args } &= help "Build the project" &= auto mode = cmdArgsMode $ modes [build,wipe,test_] &= help "Build helper program" &= program "maker" &= summary "Maker v1.0\nMake it"Maker v1.0 Make it maker [COMMAND] ... [OPTIONS] Build helper program Common flags: -? --help Display help message -V --version Print version information maker [build] [OPTIONS] [ITEM] Build the project -j --threads=NUM Number of threads to use -r --release Release build -d --debug Debug build -p --profile Profile build maker wipe [OPTIONS] Clean all build objects maker test [OPTIONS] [ANY] Run the test suite -j --threads=NUM Number of threads to use