Software Tools in Haskell: concat

concatenate files

This page is part of a series on Software Tools in Haskell.

This post is literate Haskell; you can load the source into GHCi and play along.

As usual, we start with some imports.

-- concat: concatenate files
module Main where

import System.Environment (getArgs)
import System.Exit (exitSuccess)

concat reads a list of file names from the command line and writes the contents of these files, in order, to stdout. It takes no arguments. There is one special case: a single hyphen is interpreted as the name of stdin.

main :: IO ()
main = do
  args <- getArgs

  -- just in case
  stdin <- getContents

  let
    process name = case name of
      "-"       -> putStr stdin
      otherwise -> readFile name >>= putStr

  mapM_ process args

  exitSuccess