Difference between revisions of "Simple Unix tools"
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DonStewart (talk | contribs) (simple unix tools) |
DonStewart (talk | contribs) (style) |
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This is intended as a beginners tutorial for learning Haskell from a |
This is intended as a beginners tutorial for learning Haskell from a |
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| − | "Lets just solve things already!" point of view. |
+ | "Lets just solve things already!" point of view. The examples should |
| + | help give a flavour of the beauty and expressiveness of Haskell |
||
| + | programming. |
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<haskell> |
<haskell> |
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| Line 22: | Line 24: | ||
-- The 'cat' program |
-- The 'cat' program |
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-- |
-- |
||
| − | cat = input id |
+ | cat = input id |
-- |
-- |
||
-- Sort a file |
-- Sort a file |
||
-- |
-- |
||
| − | sort' = input sort |
+ | sort' = input sort |
-- |
-- |
||
-- Reverse a file (tac) |
-- Reverse a file (tac) |
||
-- |
-- |
||
| − | tac = input reverse |
+ | tac = input reverse |
-- |
-- |
||
-- Return the head -10 line of a file |
-- Return the head -10 line of a file |
||
-- |
-- |
||
| − | head' = input $ take 10 |
+ | head' = input $ take 10 |
-- |
-- |
||
-- Remove the first 10 lines of a file |
-- Remove the first 10 lines of a file |
||
-- |
-- |
||
| − | drop' = input $ drop 10 |
+ | drop' = input $ drop 10 |
-- |
-- |
||
-- Return the tail -1 line of a file |
-- Return the tail -1 line of a file |
||
-- |
-- |
||
| − | tail' = input $ (:[]) . last |
+ | tail' = input $ (:[]) . last |
-- |
-- |
||
-- remove duplicate lines from a file (like uniq) |
-- remove duplicate lines from a file (like uniq) |
||
-- |
-- |
||
| − | uniq = input nub |
+ | uniq = input nub |
-- |
-- |
||
-- double space a file |
-- double space a file |
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-- |
-- |
||
| − | space = input $ intersperse |
+ | space = input $ intersperse "" |
-- |
-- |
||
-- repeat the input file infintely |
-- repeat the input file infintely |
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-- |
-- |
||
| − | + | rpt = interact cycle |
|
-- |
-- |
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| Line 87: | Line 89: | ||
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) |
||
-- |
-- |
||
| − | y = interact $ map f |
+ | y = interact $ map f |
where f 'e' = '*' |
where f 'e' = '*' |
||
f c = c |
f c = c |
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| Line 93: | Line 95: | ||
-- Filter the letter 'e' from a file, like tr -d 'e' |
-- Filter the letter 'e' from a file, like tr -d 'e' |
||
-- |
-- |
||
| − | tr = interact $ filter (/= 'e') |
+ | tr = interact $ filter (/= 'e') |
-- |
-- |
||
-- Count number of characters in a file (like wc -c) |
-- Count number of characters in a file (like wc -c) |
||
-- |
-- |
||
| − | wc_c = interact $ show . length |
+ | wc_c = interact $ show . length |
-- |
-- |
||
-- Count number of lines in a file, like wc -l |
-- Count number of lines in a file, like wc -l |
||
-- |
-- |
||
| − | wc_l = interact $ show . length . lines |
+ | wc_l = interact $ show . length . lines |
-- |
-- |
||
-- Count number of words in a file (like wc -w) |
-- Count number of words in a file (like wc -w) |
||
-- |
-- |
||
| − | wc_w = interact $ show . length . words |
+ | wc_w = interact $ show . length . words |
-- |
-- |
||
-- grep lines matching "^foo" from a file |
-- grep lines matching "^foo" from a file |
||
-- |
-- |
||
| − | grep = input $ filter (isPrefixOf "foo") |
+ | grep = input $ filter (isPrefixOf "foo") |
-- |
-- |
||
-- grep lines that don't match "^foo" (grep -v) |
-- grep lines that don't match "^foo" (grep -v) |
||
-- |
-- |
||
| − | grep_v= input $ filter (not . isPrefixOf "foo") |
+ | grep_v = input $ filter (not . isPrefixOf "foo") |
-- |
-- |
||
-- number each line of a file |
-- number each line of a file |
||
-- |
-- |
||
| − | num = input $ zipWith ((. (' ':)) . shows) [1..] |
+ | num = input $ zipWith ((. (' ':)) . shows) [1..] |
-- |
-- |
||
-- Compute a simple cksum of a file |
-- Compute a simple cksum of a file |
||
-- |
-- |
||
| − | main = interact $ printf "%u\n" . foldl' k 5381 |
+ | main = interact $ printf "%u\n" . foldl' k 5381 |
where k h c = h * 33 + fromIntegral (ord c) :: Int |
where k h c = h * 33 + fromIntegral (ord c) :: Int |
||
</haskell> |
</haskell> |
||
Revision as of 06:54, 22 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 elegant Haskell
--
import Data.List
import Data.Char
import System.IO
import Text.Printf
--
-- First, a useful helper
--
input f = interact (unlines . f . lines)
--
-- The 'cat' program
--
cat = input id
--
-- Sort a file
--
sort' = input sort
--
-- Reverse a file (tac)
--
tac = input reverse
--
-- Return the head -10 line of a file
--
head' = input $ take 10
--
-- Remove the first 10 lines of a file
--
drop' = input $ drop 10
--
-- Return the tail -1 line of a file
--
tail' = input $ (:[]) . last
--
-- remove duplicate lines from a file (like uniq)
--
uniq = input nub
--
-- double space a file
--
space = input $ intersperse ""
--
-- repeat the input file infintely
--
rpt = interact cycle
--
-- remove the first occurence of the line "str"
--
remove = input $ delete "str"
--
-- make a file all upper case
--
upper = interact $ map toUpper
--
-- remove leading space from each line
--
clean = input $ map (dropWhile isSpace)
--
-- join lines of a file
--
join = input $ (:[]) . 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')
--
-- Count number of characters in a file (like wc -c)
--
wc_c = interact $ show . length
--
-- Count number of lines in a file, like wc -l
--
wc_l = interact $ show . length . lines
--
-- Count number of words in a file (like wc -w)
--
wc_w = interact $ show . length . words
--
-- grep lines matching "^foo" from a file
--
grep = input $ filter (isPrefixOf "foo")
--
-- grep lines that don't match "^foo" (grep -v)
--
grep_v = input $ filter (not . isPrefixOf "foo")
--
-- number each line of a file
--
num = input $ zipWith ((. (' ':)) . shows) [1..]
--
-- Compute a simple cksum of a file
--
main = interact $ printf "%u\n" . foldl' k 5381
where k h c = h * 33 + fromIntegral (ord c) :: Int