Difference between revisions of "Simple Unix tools"
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import Text.Printf |
import Text.Printf |
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import System.Environment |
import System.Environment |
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+ | import Text.Regex.Posix |
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− | |||
+ | |||
− | -- First, |
+ | -- First, three helpers |
io f = interact (unlines . f . lines) |
io f = interact (unlines . f . lines) |
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+ | |||
− | |||
showln = (++ "\n") . show |
showln = (++ "\n") . show |
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+ | |||
− | |||
+ | regexBool r l = l =~ r :: Bool -- simple boolean regex matching |
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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 = nub -- Warning: Unix uniq discards *consecutive* dupes |
+ | uniq = nub -- Warning: Unix uniq discards *consecutive* dupes, |
+ | -- but 'nub' discards all dupes. |
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− | |||
+ | |||
-- repeat the input file infinitely |
-- repeat the input file infinitely |
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rpt = cycle |
rpt = cycle |
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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' = take 10 |
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' = drop 10 |
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' = 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' = last |
tail' = last |
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+ | |||
− | |||
-- return the last ten lines of a file |
-- return the last ten lines of a file |
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tail10 = drop =<< subtract 10 . length |
tail10 = drop =<< subtract 10 . length |
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+ | |||
− | |||
-- Reverse lines in a file (tac) |
-- Reverse lines in a file (tac) |
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tac = reverse |
tac = reverse |
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+ | |||
− | |||
-- Reverse characters on each line (rev) |
-- Reverse characters on each line (rev) |
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rev = map reverse |
rev = map reverse |
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+ | |||
− | |||
-- Reverse words on each line |
-- Reverse words on each line |
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rev_w = map (unwords . reverse . words) |
rev_w = 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 = showln . length |
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 = showln . length . lines |
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 = showln . length . words |
wc_w = showln . length . words |
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+ | |||
− | |||
-- double space a file |
-- double space a file |
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space = intersperse "" |
space = intersperse "" |
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+ | |||
− | |||
-- undo double space |
-- undo double space |
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unspace = filter (not.null) |
unspace = filter (not.null) |
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+ | |||
− | |||
-- remove the first occurrence of the line "str" |
-- remove the first occurrence of the line "str" |
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remove = delete |
remove = delete |
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+ | |||
− | |||
-- make a string all upper case |
-- make a string all upper case |
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upper = map toUpper |
upper = map toUpper |
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+ | |||
− | |||
-- remove leading space from each line |
-- remove leading space from each line |
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clean = map (dropWhile isSpace) |
clean = map (dropWhile isSpace) |
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+ | |||
− | |||
-- remove trailing whitespace |
-- remove trailing whitespace |
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clean' = map (reverse . dropWhile isSpace . reverse) |
clean' = map (reverse . dropWhile isSpace . reverse) |
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+ | |||
− | |||
-- delete leading and trailing whitespace |
-- delete leading and trailing whitespace |
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clean'' = map (f . f) |
clean'' = map (f . f) |
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where f = reverse . dropWhile isSpace |
where f = reverse . dropWhile isSpace |
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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 = map (s ++) |
blank = map (s ++) |
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where s = replicate 8 ' ' |
where s = replicate 8 ' ' |
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+ | |||
− | |||
-- join lines of a file |
-- join lines of a file |
||
join = return . concat |
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 a b = interact (map f) |
tr a b = interact (map f) |
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where f c = if c == a then b else c |
where f c = if c == a then b else c |
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+ | |||
− | |||
-- Delete characters from a string. |
-- Delete characters from a string. |
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tr_d a = tr a ' ' |
tr_d a = tr a ' ' |
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− | -- |
+ | -- lines matching the regular expression "[bf]oo" from a file |
− | grep = filter ( |
+ | grep = filter (regexBool "[bf]oo") |
+ | |||
− | |||
− | -- |
+ | -- lines not matching the regular expression "[bf]oo" from a file |
− | grep_v = filter (not . |
+ | grep_v = filter (not . regexBool "[bf]oo") |
+ | |||
− | |||
-- number each line of a file |
-- number each line of a file |
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num = zipWith (printf "%3d %s") [(1::Int)..] |
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 = foldl' k 5381 |
cksum = foldl' k 5381 |
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where k h c = h * 33 + ord c |
where k h c = h * 33 + ord c |
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+ | |||
− | |||
-- And our main wrapper |
-- And our main wrapper |
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main = do |
main = do |
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,("reverse", io rev ) |
,("reverse", io rev ) |
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,("reverseword", io rev_w ) |
,("reverseword", io rev_w ) |
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+ | ,("rpt", io rpt ) |
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− | ,("rpt", <span class="plainlinks">[http://xstretchmarks.com/stretch-mark-removal/ <span style="color:black;font-weight:normal;text-decoration:none!important;background:none!important; text-decoration:none;">click here</span>]</span> io rpt ) |
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,("sort", interact sort ) |
,("sort", interact sort ) |
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,("space", io space ) |
,("space", io space ) |
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,("wc_w", interact wc_w ) |
,("wc_w", interact wc_w ) |
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] |
] |
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+ | |||
</haskell> |
</haskell> |
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* [[Checking for correct invocation of a command line haskell program]] |
* [[Checking for correct invocation of a command line haskell program]] |
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* [[Poor man's here document]] |
* [[Poor man's here document]] |
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− | * [http://andrew.bromage.org/darcs/diff Diff in 120 Lines of Haskell] |
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[[Category:Tutorials]] |
[[Category:Tutorials]] |
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[[Category:Code]] |
[[Category:Code]] |
Latest revision as of 05:27, 8 February 2016
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.
import Control.Monad.Instances
import Data.List
import Data.Char
import Data.Maybe
import Text.Printf
import System.Environment
import Text.Regex.Posix
-- First, three helpers
io f = interact (unlines . f . lines)
showln = (++ "\n") . show
regexBool r l = l =~ r :: Bool -- simple boolean regex matching
-- remove duplicate lines from a file (like uniq)
uniq = nub -- Warning: Unix uniq discards *consecutive* dupes,
-- but 'nub' discards all dupes.
-- repeat the input file infinitely
rpt = cycle
-- Return the head -10 line of a file
take' = take 10
-- Remove the first 10 lines of a file
drop' = drop 10
-- Return the head -1 line of a file
head' = head
-- Return the tail -1 line of a file
tail' = last
-- return the last ten lines of a file
tail10 = drop =<< subtract 10 . length
-- Reverse lines in a file (tac)
tac = reverse
-- Reverse characters on each line (rev)
rev = map reverse
-- Reverse words on each line
rev_w = map (unwords . reverse . words)
-- Count number of characters in a file (like wc -c)
wc_c = showln . length
-- Count number of lines in a file, like wc -l
wc_l = showln . length . lines
-- Count number of words in a file (like wc -w)
wc_w = showln . length . words
-- double space a file
space = intersperse ""
-- undo double space
unspace = filter (not.null)
-- remove the first occurrence of the line "str"
remove = delete
-- make a string all upper case
upper = map toUpper
-- remove leading space from each line
clean = map (dropWhile isSpace)
-- remove trailing whitespace
clean' = map (reverse . dropWhile isSpace . reverse)
-- delete leading and trailing whitespace
clean'' = map (f . f)
where f = reverse . dropWhile isSpace
-- insert blank space at beginning of each line
blank = map (s ++)
where s = replicate 8 ' '
-- join lines of a file
join = return . concat
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed)
tr a b = interact (map f)
where f c = if c == a then b else c
-- Delete characters from a string.
tr_d a = tr a ' '
-- lines matching the regular expression "[bf]oo" from a file
grep = filter (regexBool "[bf]oo")
-- lines not matching the regular expression "[bf]oo" from a file
grep_v = filter (not . regexBool "[bf]oo")
-- number each line of a file
num = zipWith (printf "%3d %s") [(1::Int)..]
-- Compute a simple cksum of a file
cksum = foldl' k 5381
where k h c = h * 33 + ord c
-- And our main wrapper
main = do
who <- getProgName
maybe (return ()) id $ lookup who $
[("blank", io blank )
,("cksum", interact (showln . cksum) )
,("clean", io clean'' )
,("echo" , interact id )
,("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 rev_w )
,("reverse", io rev )
,("reverseword", io rev_w )
,("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 (tr_d . 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 )
]
How to run
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 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; ln -s UnixTools cat"
) and then run those commands ("./echo foo | ./cat"
would produce output of "foo").
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
- Checking for correct invocation of a command line haskell program
- Poor man's here document