Cat
June 8, 2012
This is easy, except that we have no way to implement the buffered input, so we ignore any -u argument that might be present. Here’s the program:
#! /usr/bin/scheme --script
(define (do-file file-name)
(let ((p (if (string=? file-name "-")
(current-input-port)
(open-input-file file-name))))
(do ((c (read-char p) (read-char p)))
((eof-object? c))
(display c))
(close-input-port p)))
(let ((args (if (and (pair? (cdr (command-line)))
(string=? (cadr (command-line)) "-u"))
(cddr (command-line))
(cdr (command-line)))))
(if (null? args)
(do-file "-")
(do ((args args (cdr args)))
((null? args))
(do-file (car args)))))
The header line and the (command-line) function are non-standard Scheme and are unique to Chez Scheme, though all Scheme systems provide something similar; (command-line) returns the command line by which the program was called, including the name of the program in its car. Variable args is set to the list of file name arguments passed on the command line, an empty argument list is handled specially, and function do-file processes a single file after setting the input port appropriately.
You can see the program at http://programmingpraxis.codepad.org/HS4bHJFl.
Programming Praxis 
My Haskell solution. Ignores the “-u” switch.
import System.Environment
import System.IO
import Control.Exception
parseCmd :: [String] -> IO [Handle]
parseCmd [] = return []
parseCmd ["-"] = return [stdin]
parseCmd ("-u":xs) = parseCmd xs
parseCmd xs = mapM (`openFile` ReadMode) xs
main :: IO ()
main = do
args hGetContents h >>= putStr))
Ok, something went wrong while posting. Let’s try again.
import System.Environment import System.IO import Control.Exception parseCmd :: [String] -> IO [Handle] parseCmd [] = return [] parseCmd ["-"] = return [stdin] parseCmd ("-u":xs) = parseCmd xs parseCmd xs = mapM (`openFile` ReadMode) xs main :: IO () main = do args <- getArgs bracket (parseCmd args) (mapM_ hClose) (mapM_ (\h -> hGetContents h >>= putStr))