hwk
Commandline text processing with Haskell functions
LTS Haskell 22.43: | 0.6 |
Stackage Nightly 2024-12-05: | 0.6 |
Latest on Hackage: | 0.6 |
hwk-0.6@sha256:045dfc284fa10f7b4dd639d30972f3a1d533c88112f041424887efd8f4c62104,1958
Module documentation for 0.6
There are no documented modules for this package.
hwk
hwk (pronounced “hawk”) is a simple Haskell-based commandline text processing tool, somewhat similar to tools like awk, grep, sed.
hwk
applies composed pure Haskell functions to a list of lines of input, enabling text processing without having to remember an obscure DSL or awkward cli options. This tool can also help to encourage people to think functionally.
hwk was originally written by Lukas Martinelli in 2016-2017: see the original README file.
hwk is pretty similar to Hawk, so you may also want to try that for a different more sophisticated monadic implementation. Some of main differences are:
- hwk uses String for input for type simplicity, whereas hawk uses ByteString
- hawk has special options for controlling input and output field/lines delimiters, whereas in hwk everything is roughly just
[String] -> [String]
(more details below) - by default hwk applies a function to the list of all the lines of stdin:
hwk -l
corresponds tohawk -m
andhawk -a
tohwk
.hwk -a
applies the function to the whole stdin.
Examples
Some simple use-cases are in the examples directory.
Change and append a string to each line:
$ seq 0 2 | hwk --line '(++ ".txt") . show . (+1) . int'
1.txt
2.txt
3.txt
or without line-mode: hwk 'map ((++ ".txt") . show . (+1) . int)'
.
Sum all negative numbers:
$ seq -100 100 | hwk 'sum . filter (< 0) . ints'
-5050
The ints function transforms a list of strings into a list of ints
Factorials in your shell scripts!:
$ seq 10 12 | hwk --line 'let {fact 0 = 1; fact n = n * fact (n - 1)} in fact . int'
3628800
39916800
479001600
Extract data from a file:
$ cat /etc/passwd | hwk -l 'reverse . filter (/= "x") . take 3 . splitOn ":"' | head -3
0 root
1 bin
2 daemon
(uses splitOn
from the extra library; -l
is the short form of --line
).
The argument passed to hwk
must be a valid Haskell function: a function that takes a list of strings and returns a new list or a single value.
Check whether the input contains a certain string:
$ cat /etc/passwd | hwk --all 'bool "no" "yes" . isInfixOf "1000"'
yes
You can also type-check functions:
$ hwk --typecheck take
Int -> [a] -> [a]
or expressions:
$ hwk -t [1,2]
Num a => [a]
And evaluate expressions:
$ hwk -e '2 ^ 32 `div` 1024'
4194304
Run commands:
$ hwk --run getCurrentDirectory
/home/user/src
Configuration
hwk
uses a Haskell configuration file ~/.config/hwk/Hwk.hs
which provides the context for the hint evaluation of the supplied function. Hint (ghci) checks the current directory first when loading, so one can override the configuration on a directory basis.
The first time hwk is run it sets up ~/.config/hwk/Hwk.hs
.
The default Hwk module configuration imports
Prelude
, Data.List
, Data.Char
, and System.FilePath
into the hint interpreter.
You can add other modules to import to userModules
or
define your own functions to use in hwk expressions if you wish.
After a hwk version update you may need or wish to sync up your Hwk.hs file to take account of any new changes: a copy of the latest default Hwk.hs is also put in ~/.config/hwk/
with version suffix.
One can specify -c
/--config-dir
to load Hwk.hs from a different location.
Installation
Either use the install.sh
script, or install by cabal-install or stack
as described below:
install.sh script from source tree or git
Use stack unpack hwk
or git clone https://github.com/juhp/hwk
.
Then go to the source directory and run the install.sh
script, which first runs stack install
, then moves the binary installed by stack install
to ~/.local/lib/hwk
, and sets up a wrapper script ~/.local/bin/hwk
which runs it.
If you wish you can change the resolver in stack.yaml first: it is also used to determine the resolver used by the created hwk
wrapper script.
cabal
If you are on a Linux distro with a system installed ghc and Haskell libaries,
you can install with cabal install
to make use of them.
stack
Installing and running with stack is better if you do not have a system ghc and/or global system Haskell libraries installed.
If you prefer not to use install.sh
in the source dir,
you can install by hand: run stack install
,
and then run it with stack exec hwk ...
using the same resolver.
How does hwk
work?
hwk
use the hint library to apply haskell functions to input.- By default it splits the input to a list of lines and applies the function to them
- Use
-a
or--all
to apply a function to all the input, or-l
/--line
to map the function on each line separately, or-w
/--words
to map the function on each line of words, - If you pass file arguments, their contents will be read and passed to the function.
- You can also typecheck the function or an expression with
-t
/--typecheck
, evaluate an expr with-e
/--eval
, or-r
/--run
an IO statement.
Note the equivalences:
hwk 'f . unlines'
==hwk -a f
hwk 'map f'
==hwk -l f
hwk -a 'f . lines'
==hwk f
hwk -l 'f . words'
==hwk -w f
hwk 'map (f . words)'
==hwk -w f
Supported return types
The following return values are supported:
String
[String]
[[String]]
Int
[Int]
[[Int]]
Contribute
Open an issue or pull request at https://github.com/juhp/hwk to report problems or make suggestions and contributions.
Usage example contributions are also welcome.
Related/alternative projects
- https://github.com/gelisam/hawk
- https://github.com/bawolk/hsp
- https://en.wikipedia.org/wiki/AWK
- https://en.wikipedia.org/wiki/Sed
- https://code.google.com/p/pyp/
Changes
Version history for hwk
0.6 (2021-06-14)
- add –words mode: applies function to list of words in each line
- experimental shell mode
- initial config fixes
0.5 (2020-10-13)
- file arguments can now provide input
- experimental –run mode to execute IO
- eval no longer prints type
- add –config-dir option
0.4 (2020-10-12)
- add –eval mode
- refactor: drop ToList and ToString classes
- import Data.List.Extra by default
- –all: remove trailing newline
- add examples/
0.3 (2020-10-11)
- add –line mode: takes a function on a String - applied to every line
- uses new ToString class (not ToList)
- add –type-check: prints the type of a given function
0.2 (2020-10-10)
- first release by Jens Petersen
- uses hint library and Hwk configuration module
0.1.0.0 (2016-2017)
- original project by Lukas Martinelli https://github.com/lukasmartinelli/hwk