Difference between revisions of "Simple Unix tools"
(please won't someone think of the apostrophes?) |
(improve the code in general, add type sigs, remove mislieading cat definition, and add a busybox style of running from a commandline) |
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Or, one could define 'main' to be a chosen tool/function (add a line to the effect that "main = wc_l") and then compile the tool with |
Or, one could define 'main' to be a chosen tool/function (add a line to the effect that "main = wc_l") and then compile the tool with |
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$ ghc --make UnixTools.hs |
$ ghc --make UnixTools.hs |
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+ | |||
+ | The given Haskell codes presents yet a third way of doing things: much like the BusyBox[http://en.wikipedia.org/wiki/BusyBox] suite of Unix tools, it is possible to compile a single monolithic binary and have it detect what name it is run by and then act appropriately. This is the approach the following code takes: you can compile it and then make symbolic links (like "ln -s UnixTools echo") and then run those commands ("echo foo | ./echo" would produce output of "foo"). |
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<haskell> |
<haskell> |
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− | -- |
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-- Some Unix-like tools written in simple, clean Haskell |
-- Some Unix-like tools written in simple, clean Haskell |
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+ | module Main |
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− | -- |
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+ | where |
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− | -- |
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+ | import Data.List ( sort, nub, intersperse, delete, isPrefixOf, foldl' ) |
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+ | import Data.Char ( toUpper, isSpace, ord ) |
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+ | --import System.IO --not needed yet |
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+ | import Text.Printf ( printf ) |
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+ | import System.Environment ( getProgName ) |
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+ | main = do |
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− | import Data.List |
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+ | calledBy <- getProgName |
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− | import Data.Char |
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+ | case calledBy of |
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− | import System.IO |
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+ | "blank" -> io blank |
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− | import Text.Printf |
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+ | "cksum" -> cksum |
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+ | "clean" -> io clean'' |
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+ | "echo" -> interact id -- not perfect. what if echoed thing is an argument and not on stdin? |
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+ | "drop" -> interact drop' |
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+ | "grep" -> io grep |
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+ | "grep -v" -> io grep_v |
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+ | "head" -> io (return . head') |
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+ | "join" -> io join |
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+ | "num" -> io num |
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+ | --"remove" -> io remove "str" |
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+ | "revw" -> io revw |
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+ | "reverse" -> io rev |
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+ | "reverseword" -> io revw |
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+ | "rpt" -> io rpt |
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+ | "sort" -> interact sort |
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+ | "space" -> io space |
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+ | "tac" -> interact tac |
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+ | "take" -> io take' |
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+ | "tail" -> io (return . tail') |
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+ | --"tr" -> interact tr |
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+ | --"tr -d" -> interact (trd . unwords) |
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+ | "unspace" -> io unspace |
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+ | "upper" -> interact upper |
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+ | "uniq" -> interact uniq |
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+ | "wc_c" -> interact wc_c |
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+ | "wc_l" -> interact wc_l |
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+ | "wc_w" -> interact wc_w |
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− | -- |
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-- First, two helpers |
-- First, two helpers |
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+ | io :: ([String] -> [String]) -> IO () |
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− | -- |
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− | io f |
+ | io f = interact (unlines . f . lines) |
+ | |||
+ | showln :: Int -> String |
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showln = (++ "\n") . show |
showln = (++ "\n") . show |
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− | -- |
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− | -- The 'cat' program |
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− | -- |
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− | cat = interact id |
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− | |||
− | -- |
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-- Sort a file |
-- Sort a file |
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+ | sort' :: String -> String |
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− | -- |
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− | sort' = |
+ | sort' = sort |
− | -- |
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-- remove duplicate lines from a file (like uniq) |
-- remove duplicate lines from a file (like uniq) |
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+ | uniq :: String -> String |
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− | -- |
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− | uniq |
+ | uniq = nub |
+ | -- repeat the input file infinitely |
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− | -- |
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+ | rpt :: [a] -> [a] |
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− | -- repeat the input file infinitely |
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+ | rpt = cycle |
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− | -- |
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− | rpt = interact cycle |
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− | -- |
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-- Return the head -10 line of a file |
-- Return the head -10 line of a file |
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+ | take' :: [String] -> [String] |
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− | -- |
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− | take' = |
+ | take' = take 10 |
− | -- |
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-- Remove the first 10 lines of a file |
-- Remove the first 10 lines of a file |
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+ | drop' :: String -> String |
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− | -- |
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− | drop' = |
+ | drop' = drop 10 |
− | -- |
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-- Return the head -1 line of a file |
-- Return the head -1 line of a file |
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+ | head' :: [String] -> String |
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− | -- |
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− | head' = |
+ | head' = head |
− | -- |
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-- Return the tail -1 line of a file |
-- Return the tail -1 line of a file |
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+ | tail' :: [String] -> String |
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− | -- |
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− | tail' = |
+ | tail' = last |
− | -- |
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-- Reverse lines in a file (tac) |
-- Reverse lines in a file (tac) |
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+ | tac :: String -> String |
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− | -- |
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− | tac |
+ | tac = reverse |
− | -- |
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-- Reverse characters on each line (rev) |
-- Reverse characters on each line (rev) |
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+ | rev :: [String] -> [String] |
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− | -- |
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− | rev |
+ | rev = map reverse |
− | -- |
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-- Reverse words on each line |
-- Reverse words on each line |
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+ | revw :: [String] -> [String] |
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− | -- |
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− | revw |
+ | revw = map (unwords. reverse . words) |
− | -- |
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-- Count number of characters in a file (like wc -c) |
-- Count number of characters in a file (like wc -c) |
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+ | wc_c :: String -> String |
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− | -- |
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− | wc_c |
+ | wc_c = showln . length |
− | -- |
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-- Count number of lines in a file, like wc -l |
-- Count number of lines in a file, like wc -l |
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+ | wc_l :: String -> String |
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− | -- |
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− | wc_l |
+ | wc_l = showln . length . lines |
− | -- |
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-- Count number of words in a file (like wc -w) |
-- Count number of words in a file (like wc -w) |
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+ | wc_w :: String -> String |
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− | -- |
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− | wc_w |
+ | wc_w = showln . length . words |
− | -- |
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-- double space a file |
-- double space a file |
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+ | space :: [String] -> [String] |
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− | -- |
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− | space |
+ | space = intersperse "" |
− | -- |
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-- undo double space |
-- undo double space |
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+ | unspace :: [String] -> [String] |
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− | -- |
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− | unspace = |
+ | unspace = filter (not.null) |
+ | -- remove the first occurrence of the line "str" |
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− | -- |
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− | + | remove :: String -> [String] -> [String] |
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+ | remove a = delete a |
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− | -- |
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− | remove = io (delete "str") |
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+ | -- make a string all upper case |
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− | -- |
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+ | upper :: String -> String |
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− | -- make a file all upper case |
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+ | upper = map toUpper |
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− | -- |
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− | upper = interact (map toUpper) |
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− | -- |
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-- remove leading space from each line |
-- remove leading space from each line |
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+ | clean :: [String] -> [String] |
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− | -- |
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− | clean = |
+ | clean = map (dropWhile isSpace) |
− | -- |
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-- remove trailing whitespace |
-- remove trailing whitespace |
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+ | clean' :: [String] -> [String] |
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− | -- |
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− | clean' = |
+ | clean' = (map f) |
− | + | where f = reverse . dropWhile isSpace . reverse |
|
− | -- |
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-- delete leading and trailing whitespace |
-- delete leading and trailing whitespace |
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+ | clean'' :: [String] -> [String] |
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− | -- |
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− | clean'' = |
+ | clean'' = map (f . f) |
− | + | where f = reverse . dropWhile isSpace |
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− | -- |
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-- insert blank space at beginning of each line |
-- insert blank space at beginning of each line |
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+ | blank :: [String] -> [String] |
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− | -- |
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− | blank = |
+ | blank = map (s ++) |
− | + | where s = replicate 8 ' ' |
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− | -- |
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-- join lines of a file |
-- join lines of a file |
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+ | join :: [String] -> [String] |
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− | -- |
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− | join |
+ | join = return . concat |
− | -- |
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-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
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+ | tr :: Char -> Char -> IO () |
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− | -- |
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− | + | tr a b = interact (map f) |
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+ | where f c = if c == a then b else c |
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− | where f 'e' = '*' |
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+ | |||
− | f c = c |
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+ | -- Delete characters from a string. |
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− | -- |
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+ | trd :: Char -> IO () |
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− | -- Filter the letter 'e' from a file, like tr -d 'e' |
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+ | trd a = tr a ' ' |
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− | -- |
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− | tr = interact $ filter (/= 'e') |
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− | -- |
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-- grep lines matching "^foo" from a file |
-- grep lines matching "^foo" from a file |
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+ | grep :: [String] -> [String] |
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− | -- |
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− | grep |
+ | grep = filter (isPrefixOf "foo") |
− | -- |
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-- grep lines that don't match "^foo" (grep -v) |
-- grep lines that don't match "^foo" (grep -v) |
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+ | grep_v :: [String] -> [String] |
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− | -- |
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− | grep_v = |
+ | grep_v = filter (not . isPrefixOf "foo") |
− | -- |
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-- number each line of a file |
-- number each line of a file |
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+ | num :: [String] -> [String] |
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− | -- |
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− | num |
+ | num = zipWith (printf "%3d %s") [(1::Int)..] |
− | -- |
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-- Compute a simple cksum of a file |
-- Compute a simple cksum of a file |
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+ | cksum :: IO () |
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− | -- |
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cksum = interact $ showln . foldl' k 5381 |
cksum = interact $ showln . foldl' k 5381 |
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− | + | where k h c = h * 33 + ord c |
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</haskell> |
</haskell> |
Revision as of 04:38, 11 March 2007
Simple Unix commandline tools written in Haskell.
This is intended as a beginner's tutorial for learning Haskell from a "Let's just solve things already!" point of view. The examples should help give a flavor of the beauty and expressiveness of Haskell programming.
These functions can be executed as one liners from a shell. For example, to use the Haskell version of 'wc':
$ cat file.txt | ghc -e 'wc_l' UnixTools.hs
Or, one could define 'main' to be a chosen tool/function (add a line to the effect that "main = wc_l") and then compile the tool with $ ghc --make UnixTools.hs
The given Haskell codes presents yet a third way of doing things: much like the BusyBox[1] suite of Unix tools, it is possible to compile a single monolithic binary and have it detect what name it is run by and then act appropriately. This is the approach the following code takes: you can compile it and then make symbolic links (like "ln -s UnixTools echo") and then run those commands ("echo foo | ./echo" would produce output of "foo").
-- Some Unix-like tools written in simple, clean Haskell
module Main
where
import Data.List ( sort, nub, intersperse, delete, isPrefixOf, foldl' )
import Data.Char ( toUpper, isSpace, ord )
--import System.IO --not needed yet
import Text.Printf ( printf )
import System.Environment ( getProgName )
main = do
calledBy <- getProgName
case calledBy of
"blank" -> io blank
"cksum" -> cksum
"clean" -> io clean''
"echo" -> interact id -- not perfect. what if echoed thing is an argument and not on stdin?
"drop" -> interact drop'
"grep" -> io grep
"grep -v" -> io grep_v
"head" -> io (return . head')
"join" -> io join
"num" -> io num
--"remove" -> io remove "str"
"revw" -> io revw
"reverse" -> io rev
"reverseword" -> io revw
"rpt" -> io rpt
"sort" -> interact sort
"space" -> io space
"tac" -> interact tac
"take" -> io take'
"tail" -> io (return . tail')
--"tr" -> interact tr
--"tr -d" -> interact (trd . unwords)
"unspace" -> io unspace
"upper" -> interact upper
"uniq" -> interact uniq
"wc_c" -> interact wc_c
"wc_l" -> interact wc_l
"wc_w" -> interact wc_w
-- First, two helpers
io :: ([String] -> [String]) -> IO ()
io f = interact (unlines . f . lines)
showln :: Int -> String
showln = (++ "\n") . show
-- Sort a file
sort' :: String -> String
sort' = sort
-- remove duplicate lines from a file (like uniq)
uniq :: String -> String
uniq = nub
-- repeat the input file infinitely
rpt :: [a] -> [a]
rpt = cycle
-- Return the head -10 line of a file
take' :: [String] -> [String]
take' = take 10
-- Remove the first 10 lines of a file
drop' :: String -> String
drop' = drop 10
-- Return the head -1 line of a file
head' :: [String] -> String
head' = head
-- Return the tail -1 line of a file
tail' :: [String] -> String
tail' = last
-- Reverse lines in a file (tac)
tac :: String -> String
tac = reverse
-- Reverse characters on each line (rev)
rev :: [String] -> [String]
rev = map reverse
-- Reverse words on each line
revw :: [String] -> [String]
revw = map (unwords. reverse . words)
-- Count number of characters in a file (like wc -c)
wc_c :: String -> String
wc_c = showln . length
-- Count number of lines in a file, like wc -l
wc_l :: String -> String
wc_l = showln . length . lines
-- Count number of words in a file (like wc -w)
wc_w :: String -> String
wc_w = showln . length . words
-- double space a file
space :: [String] -> [String]
space = intersperse ""
-- undo double space
unspace :: [String] -> [String]
unspace = filter (not.null)
-- remove the first occurrence of the line "str"
remove :: String -> [String] -> [String]
remove a = delete a
-- make a string all upper case
upper :: String -> String
upper = map toUpper
-- remove leading space from each line
clean :: [String] -> [String]
clean = map (dropWhile isSpace)
-- remove trailing whitespace
clean' :: [String] -> [String]
clean' = (map f)
where f = reverse . dropWhile isSpace . reverse
-- delete leading and trailing whitespace
clean'' :: [String] -> [String]
clean'' = map (f . f)
where f = reverse . dropWhile isSpace
-- insert blank space at beginning of each line
blank :: [String] -> [String]
blank = map (s ++)
where s = replicate 8 ' '
-- join lines of a file
join :: [String] -> [String]
join = return . concat
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed)
tr :: Char -> Char -> IO ()
tr a b = interact (map f)
where f c = if c == a then b else c
-- Delete characters from a string.
trd :: Char -> IO ()
trd a = tr a ' '
-- grep lines matching "^foo" from a file
grep :: [String] -> [String]
grep = filter (isPrefixOf "foo")
-- grep lines that don't match "^foo" (grep -v)
grep_v :: [String] -> [String]
grep_v = filter (not . isPrefixOf "foo")
-- number each line of a file
num :: [String] -> [String]
num = zipWith (printf "%3d %s") [(1::Int)..]
-- Compute a simple cksum of a file
cksum :: IO ()
cksum = interact $ showln . foldl' k 5381
where k h c = h * 33 + ord c
Where to now?
- Haskell.org
- The Haskell standard list library, with docs
- Alternative implementations of the wc program
- Learn how to test Haskell code
- More Haskell code
- Haskell for shell scripting
- Export list functions to the shell with h4sh