Simple Unix tools: Difference between revisions
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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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-- | -- | ||
-- First, | -- First, two helpers | ||
-- | -- | ||
io f = interact (unlines . f . lines) | |||
showln = (++ "\n") . show | |||
-- | -- | ||
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-- Sort a file | -- Sort a file | ||
-- | -- | ||
sort' = | sort' = io sort | ||
-- | |||
-- remove duplicate lines from a file (like uniq) | |||
-- | |||
uniq = io nub | |||
-- | -- | ||
-- | -- repeat the input file infintely | ||
-- | -- | ||
rpt = interact cycle | |||
-- | -- | ||
-- Return the head -10 line of a file | -- Return the head -10 line of a file | ||
-- | -- | ||
take' = io (take 10) | |||
-- | -- | ||
-- Remove the first 10 lines of a file | -- Remove the first 10 lines of a file | ||
-- | -- | ||
drop' = | drop' = io (drop 10) | ||
-- | |||
-- Return the head -1 line of a file | |||
-- | |||
head' = io (return . head) | |||
-- | -- | ||
-- Return the tail -1 line of a file | -- Return the tail -1 line of a file | ||
-- | -- | ||
tail' = | tail' = io (return . last) | ||
-- | |||
-- Reverse lines in a file (tac) | |||
-- | |||
tac = io reverse | |||
-- | |||
-- Reverse characters on each line (rev) | |||
-- | |||
rev = io (map reverse) | |||
-- | |||
-- Reverse words on each line | |||
-- | |||
revw = io $ map (unwords. reverse . words) | |||
-- | |||
-- Count number of characters in a file (like wc -c) | |||
-- | |||
wc_c = interact (showln . length) | |||
-- | |||
-- Count number of lines in a file, like wc -l | |||
-- | |||
wc_l = interact (showln . length . lines) | |||
-- | -- | ||
-- | -- Count number of words in a file (like wc -w) | ||
-- | -- | ||
wc_w = interact (showln . length . words) | |||
-- | -- | ||
-- double space a file | -- double space a file | ||
-- | -- | ||
space = | space = io (intersperse "") | ||
-- | -- | ||
-- | -- undo double space | ||
-- | -- | ||
unspace = io $ filter (not.null) | |||
-- | -- | ||
-- remove the first occurence of the line "str" | -- remove the first occurence of the line "str" | ||
-- | -- | ||
remove = | remove = io (delete "str") | ||
-- | -- | ||
-- make a file all upper case | -- make a file all upper case | ||
-- | -- | ||
upper = interact | upper = interact (map toUpper) | ||
-- | -- | ||
-- remove leading space from each line | -- remove leading space from each line | ||
-- | -- | ||
clean = | clean = io $ map (dropWhile isSpace) | ||
-- | -- | ||
-- | -- remove trailing whitespace | ||
-- | -- | ||
clean' = io (map f) | |||
where f = reverse . dropWhile isSpace . reverse | |||
-- | -- | ||
-- | -- delete leading and trailing whitespace | ||
-- | -- | ||
clean'' = io $ map (f . f) | |||
where f | where f = reverse . dropWhile isSpace | ||
-- | -- | ||
-- | -- insert blank space at beginning of each line | ||
-- | -- | ||
blank = io $ map (s ++) | |||
where s = replicate 8 ' ' | |||
-- | -- | ||
-- | -- join lines of a file | ||
-- | -- | ||
join = io (return . concat) | |||
-- | -- | ||
-- | -- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) | ||
-- | -- | ||
y = interact (map f) | |||
where f 'e' = '*' | |||
f c = c | |||
-- | -- | ||
-- | -- Filter the letter 'e' from a file, like tr -d 'e' | ||
-- | -- | ||
tr = interact $ filter (/= 'e') | |||
-- | -- | ||
-- grep lines matching "^foo" from a file | -- grep lines matching "^foo" from a file | ||
-- | -- | ||
grep = | grep = io $ filter (isPrefixOf "foo") | ||
-- | -- | ||
-- grep lines that don't match "^foo" (grep -v) | -- grep lines that don't match "^foo" (grep -v) | ||
-- | -- | ||
grep_v = | grep_v = io $ filter (not . isPrefixOf "foo") | ||
-- | -- | ||
-- number each line of a file | -- number each line of a file | ||
-- | -- | ||
num = | num = io $ zipWith (printf "%3d %s") [(1::Int)..] | ||
-- | -- | ||
-- Compute a simple | -- Compute a simple cksum of a file | ||
-- | -- | ||
cksum = interact $ | cksum = interact $ showln . foldl' k 5381 | ||
where k h c = h * 33 + | where k h c = h * 33 + ord c | ||
</haskell> | </haskell> | ||
'''Where to now?''' | '''Where to now?''' | ||
Revision as of 13:54, 23 September 2006
Simple unix tools written in Haskell.
This is intended as a beginners tutorial for learning Haskell from a "Lets just solve things already!" point of view. The examples should help give a flavour of the beauty and expressiveness of Haskell programming.
--
-- Some unix-like tools written in simple, clean Haskell
--
--
import Data.List
import Data.Char
import System.IO
import Text.Printf
--
-- First, two helpers
--
io f = interact (unlines . f . lines)
showln = (++ "\n") . show
--
-- The 'cat' program
--
cat = interact id
--
-- Sort a file
--
sort' = io sort
--
-- remove duplicate lines from a file (like uniq)
--
uniq = io nub
--
-- repeat the input file infintely
--
rpt = interact cycle
--
-- Return the head -10 line of a file
--
take' = io (take 10)
--
-- Remove the first 10 lines of a file
--
drop' = io (drop 10)
--
-- Return the head -1 line of a file
--
head' = io (return . head)
--
-- Return the tail -1 line of a file
--
tail' = io (return . last)
--
-- Reverse lines in a file (tac)
--
tac = io reverse
--
-- Reverse characters on each line (rev)
--
rev = io (map reverse)
--
-- Reverse words on each line
--
revw = io $ map (unwords. reverse . words)
--
-- Count number of characters in a file (like wc -c)
--
wc_c = interact (showln . length)
--
-- Count number of lines in a file, like wc -l
--
wc_l = interact (showln . length . lines)
--
-- Count number of words in a file (like wc -w)
--
wc_w = interact (showln . length . words)
--
-- double space a file
--
space = io (intersperse "")
--
-- undo double space
--
unspace = io $ filter (not.null)
--
-- remove the first occurence of the line "str"
--
remove = io (delete "str")
--
-- make a file all upper case
--
upper = interact (map toUpper)
--
-- remove leading space from each line
--
clean = io $ map (dropWhile isSpace)
--
-- remove trailing whitespace
--
clean' = io (map f)
where f = reverse . dropWhile isSpace . reverse
--
-- delete leading and trailing whitespace
--
clean'' = io $ map (f . f)
where f = reverse . dropWhile isSpace
--
-- insert blank space at beginning of each line
--
blank = io $ map (s ++)
where s = replicate 8 ' '
--
-- join lines of a file
--
join = io (return . concat)
--
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed)
--
y = interact (map f)
where f 'e' = '*'
f c = c
--
-- Filter the letter 'e' from a file, like tr -d 'e'
--
tr = interact $ filter (/= 'e')
--
-- grep lines matching "^foo" from a file
--
grep = io $ filter (isPrefixOf "foo")
--
-- grep lines that don't match "^foo" (grep -v)
--
grep_v = io $ filter (not . isPrefixOf "foo")
--
-- number each line of a file
--
num = io $ zipWith (printf "%3d %s") [(1::Int)..]
--
-- Compute a simple cksum of a file
--
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