grep.hs

module Main where 
    
import System (getArgs)
import Text.RegexPR

-- matches lines against a pattern
grep :: String -> [String] -> [String]
grep p = filter $ match
    where match s = case matchRegexPR p s of
                        Just _ -> True
                        Nothing -> False

-- take standard in filter through grep, out to standard out
main :: IO ()
main = do
    args <- getArgs
    let [pattern] = args
    interact $ unlines . (grep pattern) . lines