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https://github.com/gelisam/hawk
Haskell text processor for the command-line
https://github.com/gelisam/hawk
Last synced: about 23 hours ago
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Haskell text processor for the command-line
- Host: GitHub
- URL: https://github.com/gelisam/hawk
- Owner: gelisam
- License: apache-2.0
- Created: 2013-08-03T00:48:32.000Z (over 11 years ago)
- Default Branch: main
- Last Pushed: 2024-02-10T04:55:36.000Z (9 months ago)
- Last Synced: 2024-10-25T09:29:28.757Z (21 days ago)
- Language: Haskell
- Homepage:
- Size: 910 KB
- Stars: 361
- Watchers: 18
- Forks: 20
- Open Issues: 75
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
Awesome Lists containing this project
- awesome-for-oneliner - hawk - Haskell text processor for the command-line (AWK-like Tools / Open USP Tsukubai)
README
# Hawk [](https://hackage.haskell.org/package/haskell-awk) [](https://github.com/gelisam/hawk/actions)
Transform text from the command-line using Haskell expressions. Similar to [awk](http://cm.bell-labs.com/cm/cs/awkbook/index.html), but using Haskell as the text-processing language.
## Examples
In [Unix](http://en.wikipedia.org/wiki/Unix) the file `/etc/passwd` is used to
keep track of every registered user in the system. Each entry in the file
contains information about a single user, using a simple colon-separated format.
For example:
```
root:x:0:0:root:/root:/bin/bash
```
The first field is the username. We can use Hawk to list all usernames as follows:
```bash
> cat /etc/passwd | hawk -d: -m 'head'
root
```
The `-d` option tells Hawk to use `:` as field delimiters, causing the first line to be interpreted as `["root", "x", "0", "0", "root", "/root", "/bin/bash"]`.
The `-m` tells Hawk to map a function over each line of the input. In this case, the function `head` extracts the first field of the line, which happens to be the username.
We could of course have achieved identical results by using awk instead of Hawk:
```bash
> cat /etc/passwd | awk -F: '{print $1}'
root
```
While Hawk and awk have similar use cases, the philosophy behind the two is very
different. Awk uses a specialized language designed to concisely express many text transformations,
while Hawk uses the general-purpose language Haskell, which is also known for being concise, among other things.
There are many standard command-line tools that can be easily approximated using
[short Haskell expressions](https://wiki.haskell.org/Simple_Unix_tools).
Another important difference is that while awk one-liners are self-contained, Hawk encourages the use of libraries and user-defined functions. By adding function definitions, module imports and language pragmas to Hawk's user-configurable [prelude file](https://github.com/gelisam/hawk/tree/main/doc#user-prelude), those functions, libraries and language extensions become available to Hawk one-liners.
For instance, we could add a `takeLast` function extracting the last `n` elements from a list, and use it to (inefficiently) approximate `tail`:
```bash
> echo 'takeLast n = reverse . take n . reverse' >> ~/.hawk/prelude.hs
> seq 0 100 | hawk -a 'takeLast 3'
98
99
100
```
For more details, see the
[presentation](http://melrief.github.io/HawkPresentation/#/) and the
[documentation](https://github.com/gelisam/hawk/tree/main/doc/README.md).
## Installation
To install hawk, either run `stack install haskell-awk` or `cabal install haskell-awk`.
You should be ready to use Hawk:
```bash
> hawk '[1..3]'
1
2
3
```
The first run will create a default configuration file into
`~/.hawk/prelude.hs` if it doesn't exist.
## Alternatives
You can also try [hwk](https://hackage.haskell.org/package/hwk) which is fairly similar to this project though simpler.