In Haskell, you can access the command line arguments with getArgs. Check out this example.
We have to import System.Environment to get access to the getArgs function. The environment library also comes with some useful functions like getEnv and setEnv for using environment variables.
The head function pulls the first element from a list. The variable args is a list of all the commnad line arguments provided to the program at run time.
main = do
args <- getArgs
putStrLn $ head args