Difference between revisions of "Simple Unix tools"
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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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| + | -- |
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-- |
-- |
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| Line 17: | Line 18: | ||
-- |
-- |
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| − | -- First, |
+ | -- First, two helpers |
-- |
-- |
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| − | + | io f = interact (unlines . f . lines) |
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| + | showln = (++ "\n") . show |
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-- |
-- |
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| Line 29: | Line 31: | ||
-- Sort a file |
-- Sort a file |
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-- |
-- |
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| − | sort' = |
+ | sort' = io sort |
| + | |||
| + | -- |
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| ⚫ | |||
| + | -- |
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| + | uniq = io nub |
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-- |
-- |
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| − | -- |
+ | -- repeat the input file infintely |
-- |
-- |
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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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-- |
-- |
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| − | + | take' = io (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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-- |
-- |
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| − | drop' = |
+ | drop' = io (drop 10) |
| + | |||
| + | -- |
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| + | -- Return the head -1 line of a file |
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| + | -- |
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| + | head' = io (return . head) |
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-- |
-- |
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-- Return the tail -1 line of a file |
-- Return the tail -1 line of a file |
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-- |
-- |
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| − | tail' = |
+ | tail' = io (return . last) |
| + | -- |
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| ⚫ | |||
-- |
-- |
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| + | tac = io reverse |
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| ⚫ | |||
| + | |||
| + | -- |
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| + | -- Reverse characters on each line (rev) |
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-- |
-- |
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| − | + | rev = io (map reverse) |
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| + | |||
| + | -- |
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| + | -- Reverse words on each line |
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| + | -- |
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| + | revw = io $ map (unwords. reverse . words) |
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| + | |||
| + | -- |
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| + | -- Count number of characters in a file (like wc -c) |
||
| + | -- |
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| ⚫ | |||
| + | |||
| + | -- |
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| ⚫ | |||
| + | -- |
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| + | wc_l = interact (showln . length . lines) |
||
| + | |||
| + | -- |
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| + | -- Count number of words in a file (like wc -w) |
||
| + | -- |
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| + | wc_w = interact (showln . length . words) |
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-- |
-- |
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-- double space a file |
-- double space a file |
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-- |
-- |
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| − | space = |
+ | space = io (intersperse "") |
-- |
-- |
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| + | -- undo double space |
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| − | -- repeat the input file infinitely |
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-- |
-- |
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| + | unspace = io $ filter (not.null) |
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| ⚫ | |||
-- |
-- |
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-- remove the first occurence of the line "str" |
-- remove the first occurence of the line "str" |
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-- |
-- |
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| − | remove = |
+ | remove = io (delete "str") |
-- |
-- |
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-- make a file all upper case |
-- make a file all upper case |
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-- |
-- |
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| − | upper = interact |
+ | upper = interact (map toUpper) |
-- |
-- |
||
-- remove leading space from each line |
-- remove leading space from each line |
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-- |
-- |
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| − | clean = |
+ | clean = io $ map (dropWhile isSpace) |
-- |
-- |
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| + | -- remove trailing whitespace |
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| ⚫ | |||
-- |
-- |
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| + | clean' = io (map f) |
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| − | join = input $ (:[]) . concat |
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| + | where f = reverse . dropWhile isSpace . reverse |
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-- |
-- |
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| + | -- delete leading and trailing whitespace |
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| − | -- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
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-- |
-- |
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| − | + | clean'' = io $ map (f . f) |
|
| − | where f |
+ | where f = reverse . dropWhile isSpace |
| + | |||
| ⚫ | |||
-- |
-- |
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| + | -- insert blank space at beginning of each line |
||
| ⚫ | |||
-- |
-- |
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| − | + | blank = io $ map (s ++) |
|
| + | where s = replicate 8 ' ' |
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-- |
-- |
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| − | -- |
+ | -- join lines of a file |
-- |
-- |
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| − | + | join = io (return . concat) |
|
-- |
-- |
||
| − | -- |
+ | -- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
-- |
-- |
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| − | + | y = interact (map f) |
|
| + | where f 'e' = '*' |
||
| − | |||
| ⚫ | |||
-- |
-- |
||
| − | -- |
+ | -- Filter the letter 'e' from a file, like tr -d 'e' |
-- |
-- |
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| − | + | tr = interact $ filter (/= 'e') |
|
-- |
-- |
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-- grep lines matching "^foo" from a file |
-- grep lines matching "^foo" from a file |
||
-- |
-- |
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| − | grep = |
+ | grep = io $ 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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-- |
-- |
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| − | grep_v = |
+ | grep_v = io $ filter (not . isPrefixOf "foo") |
-- |
-- |
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-- number each line of a file |
-- number each line of a file |
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-- |
-- |
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| − | num = |
+ | num = io $ zipWith (printf "%3d %s") [(1::Int)..] |
-- |
-- |
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| − | -- Compute a simple |
+ | -- Compute a simple cksum of a file |
-- |
-- |
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| − | cksum = interact $ |
+ | cksum = interact $ showln . foldl' k 5381 |
| − | where k h c = h * 33 + |
+ | where k h c = h * 33 + ord c |
| + | |||
</haskell> |
</haskell> |
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| + | |||
'''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