HSL

Haskell command line text processor

Tool to quickly compile and run haskell streaming text processors on the command line.

Features a powerful way of working quickly with JSON.

Examples

Poor man's tac:

> seq 3 | hsl reverse
3
2
1

The input is a [Text], a list of lines.

> echo '!LSH olleH'  | hsl 'fmap T.reverse'
Hello HSL!

The output is also an array of lines... but it could also be an array of tuples, in which case the tuples are displayed as tab-separated columns.

> printf 'helloWorld\nnicePlanet\n' | hsl "fmap (break isUpper)"
hello   World
nice    Planet

Or a single value...

> printf 'literary\ncheeseburger' | hsl 'maximumBy (comparing T.length) . concatMap T.words'
cheeseburger

Full Haskell syntax is supported. Go crazy!

> printf "hello\nworld\n" | hsl 'take 2 . repeat . filter (T.isPrefixOf "w")'
world
world

A few builtins, such as hist, are provided for convenience.

cat src/HSL/*.hs | hsl 'take 5 . sortOnR snd . hist . concatMap T.words'
=   56
->  50
::  24
Datum   21
b,  21

You can add your own builtins to src/HSL/Stdlib.hs. Send us yours in a pull request!

JSON

One of HSL's most useful builtin is json. It's like cut, but for JSON!

More concretely, if you have a file with one JSON expression per line, json lets you easily specify a path from which to extract elements.

> cat cat_memes.json 
{"name": "nyan", "year": 2011}
{"name": "longcat", "year": 2007}
{"name": "ceiling cat", "year": 2006}
{"name": "invisible bike cat", "year": 2008}
> cat cat_memes.json | hsl 'sort . json i "year"'
2006
2007
2008
2011

The i argument specifies the type of the result. i (Int), t (Text) and f (Float) are provided for this purpose. The following are equivalent:

echo '[[1,2],[3,4]]' | hsl 'json (undefined::[(Int,Int)]) ""'
1   2
3   4

echo '[[1,2],[3,4]]' | hsl 'json [(i,i)] ""'
1   2
3   4

The empty string in the above example is an empty path, referring to the entire JSON expression. The general syntax for paths is illustrated in the following example:

> echo '{"a":{"b":["Hello","World"]}}' | hsl 'json t "a b 0"'
Hello

If you need to extract more than one value per line, use json2 or json3.

> echo '{"born":1938, "age":75}' | hsl 'fmap (uncurry (+)) . json2 (i,i) "born" "age"'
2013

Tabular input

The function tabs is provided to read \t separated input. It works just like json, except you don't need to provide keys:

> printf 'a      10\nb   11\na   12' | hsl 'tally . tabs (t,i)'
a   22
b   11

Installing

> git clone 'https://github.com/ssadler/hsl.git' && cd hsl
> # Install dependencies... You probably already have them (?)
> echo 'alias hsl="'`pwd`'/hsl"' >> ~/.bashrc