# hwk ![MIT licensed](https://img.shields.io/badge/license-MIT-blue.svg)

hwk was originally written by Lukas Martinelli in 2016-2017:
see the [original README file](README.md.orig).

<img align="right" alt="hwk" src="hwk.png" />

**hwk** (pronounced "hawk") is a simple Haskell-based text stream manipulation tool, somewhat similar to tools like **awk** or **sed**.
`hwk` applies concisely composed pure functions to a list of strings from stdin. Because Haskell is lazy and has a powerful arsenal of functions, there is no need to invent another DSL. Hopefully this tool will also encourage more people to think functionally.

## Example

Change and append a string to each line:
```bash
$ 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:
```bash
$ 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!:
```bash
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:
```bash
$ cat /etc/passwd | hwk --line 'reverse . filter (/= "x") . take 3 . splitOn ":"' | head -3
0 root
1 bin
2 daemon
```
(a module defining `splitOn` from the extra or split library needs to be added to the Hwk.hs config file).

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 where input contains a certain string:
```
$ cat /etc/passwd | hwk --all 'bool "no" "yes" . isInfixOf "1000"'
yes
```

## Configuration
`hwk` uses a Haskell configuration file `~/.config/hwk/Hwk.hs` which provides the context for the hint evaluation of the supplied function.

The default configuration [Hwk module](data/Hwk.hs) just sets
the `Prelude`, `Data.List`, and `Data.Char` modules to be imported into the hint interpreter.

The first time hwk is run it sets up `~/.config/hwk/Hwk.hs`.

You can add other modules to import or define your own functions in
`~/.config/hwk/Hwk.hs`.

After a hwk version update you may wish/have to update up your Hwk.hs file to take account of new changes: a copy of the latest default Hwk.hs is also put in `~/.config/hwk/` with version suffix.

## Install
Either use the `install.sh` script, or install by cabal-install or stack
as described below:

### Install 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.

You may wish to 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 by stack is better if you do not have a system ghc
and/or global system Haskell libraries installed.

Alternatively to 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 evaluate haskell functions on standard input.
- By default it splits the input to a list of lines: `[String] -> ToList a`
- Use `-a` or `--all` to apply a function to all the input: `String -> Tolist a`

## Supported return types

By default the following instances of the `ToList` class are defined:

- `String`
- `[String]`
- `[[String]]`
- `Int`
- `[Int]`

## Contribute

Open an issue or pull request at https://github.com/juhp/hwk
to report problems or make suggestions and contributions.

## Related/alternative projects

- https://github.com/gelisam/hawk
- https://github.com/bawolk/hsp
- https://code.google.com/p/pyp/
- https://en.wikipedia.org/wiki/AWK
- https://en.wikipedia.org/wiki/Sed