jet-lang

An EDN query language.

Caution

This query language is work in progress. Consider it experimental, suited for exploratory programming, but not suited for production usage yet. The latest breaking change happened on (2019-08-05).

Introduction

The --query option allows to select or remove specific parts of the output. A query is written in jet-lang which uses EDN syntax.

These Clojure-like functions are supported in jet-lang:

• for maps: assoc, assoc-in, update, update-in, keys, vals, select-keys, dissoc, map-vals, juxt, count, into, set/rename-keys, set/join.
• for lists: first, last, take, drop, nth, map, zipmap, filter, remove, juxt, count, distinct, dedupe, conj, into.
• working with strings: str, re-find.
• logic: and, or, not, if, =, not=, >, >=, <, <=.
• literal values: quote/#jet/lit.
• copy the entire input value: identity (for short id, thanks Haskell).
• print the result of an intermediate query: jet/debug.
• arithmetic: +, -, *, /, inc, dec.

To learn more about how to use them, read the tutorial or go straight to the gallery.

Tutorial

Tip: to follow along, you can use the jet interactive shell. To start it, type jet --interactive.

In this tutorial the word list also applies to arrays and vectors.

Single values can be selected by using a key:

echo '{:a 1}' | jet --query ':a'
1

or more explicity with get:

echo '{:a 1}' | jet --query '(get :a)'
1

Numbers can be used for looking up by position in lists:

$ echo '[1 2 3]' | lein jet --query '0'
1
$ echo '[1 2 3]' | lein jet --query '100'
nil

You can also use nth for this:

$ echo '[1 2 3]' | lein jet --query '(nth #jet/lit 0)'
1

A subselection of a map can be made with select-keys:

echo '{:a 1 :b 2 :c 3}' | jet --query '(select-keys [:a :b])'
{:a 1, :b 2}

Removing keys can be achieved with dissoc:

echo '{:a 1 :b 2 :c 3}' | jet --query '(dissoc :c)'
{:a 1, :b 2}

A query can be applied to every element in a list using map:

$ echo '[{:a 1 :b 2} {:a 2 :b 3}]' | jet --query '(map (select-keys [:a]))'
[{:a 1} {:a 2}]

Associating a new key and value in a map is done with assoc:

$ echo '{:a 1}' | jet --query '(assoc :b :a)'
{:a 1, :b 1}

Updating an existing key and value can be done with update:

$ echo '{:a {:b 1}}' | jet --query '(update :a :b)'
{:a 1}

echo '{:a [1 2 3]}' | jet --query '(update :a (take #jet/lit 2))'
{:a [1 2]}

echo '{:a [1 2 3]}' | jet --query '(update :a (drop #jet/lit 2))'
{:a [3]}

echo '{:a [1 2 3]}' | jet --query '(update :a (nth #jet/lit 2))'
{:a 3}

The difference between assoc and update is that the query provided to the former begins at the root and the query provided to the latter begins at place to be updated.

There are also assoc-in and update-in which behave in similar ways but allow changing nested values:

$ echo '{:a 1}' | jet --query '(assoc-in [:b :c] :a)'
{:a 1, :b {:c 1}}

$ echo '{:a {:b [1 2 3]}}' | jet --query '(update-in [:a :b] last)'
{:a {:b 3}}

Creating a new map from scratch is done with hash-map:

$ echo '{:a 1 :b 2}' | jet --query '(hash-map :foo :a :bar :b)'
{:foo 1, :bar 2}

or using a map literal:

$ echo '{:a 1 :b 2}' | jet --query '{:foo :a :bar :b}'
{:foo 1, :bar 2}

Inserting literal values can be done with done with quote:

$ echo '{:a 1}' | jet --query '{:foo :a :bar (quote "hello")}'
{:foo 1, :bar "hello"}

or prefixing it with the tag #jet/lit:

$ echo '{:a 1}' | jet --query '{:foo :a :bar #jet/lit "hello"}'
{:foo 1, :bar "hello"}

Applying multiple queries after one another can be achieved using vector notation.

$ echo '{:a {:a/a 1 :a/b 2} :b 2}' | jet --query '[(select-keys [:a]) (update :a :a/a)]'
{:a 1}

The outer query is implicitly wrapped, so you don't have to wrap it yourself:

$ echo '{:a {:a/a 1 :a/b 2} :b 2}' | jet --query '(select-keys [:a]) (update :a :a/a)'
{:a 1}

Copy the input value:

$ echo '{:a 1}' | jet --query '{:input (identity)}'
{:input {:a 1}}

Or for short:

$ echo '{:a 1}' | jet --query '{:input (id)}'
{:input {:a 1}}

When functions with only one (implicit input) argument are used, the wrapping parens may be left out, so even shorter:

$ echo '{:a 1}' | jet --query '{:input id}'
{:input {:a 1}}

You can print the result of an intermediate query using jet/debug:

$ echo '{:a {:a/a 1 :a/b 2} :b 2}' | jet --query '(select-keys [:a]) jet/debug (update :a :a/a)'
{:a #:a{:a 1, :b 2}}
{:a 1}

Keys and values:

$ echo '{:a [1 2 3] :b [4 5 6]}' | jet --query '(keys)'
[:a :b]

$ echo '{:a [1 2 3] :b [4 5 6]}' | jet --query '(vals)'
[[1 2 3] [4 5 6]]

echo '{"foo bar": 1}' | jet --from json --to json --query '(set/rename-keys {"foo bar" "foo-bar"})'
{"foo-bar":1}

To apply a function on all map values, use map-vals:

$ echo '{:foo {:a 1 :b 2} :bar {:a 1 :b 2}}' | jet --query '(map-vals :a)'
{:foo 1 :bar 2}

Miscellaneous list functions:

echo '[1 2 3]' | jet --query '(first)'
1

echo '[1 2 3]' | jet --query '(last)'
3

echo '[[1 2 3] [4 5 6]]' | jet --query '(last)'
[4 5 6]

echo '[[1 2 3] [4 5 6]]' | jet --query '(map last)'
[3 6]

echo '[{:a 1} {:a 2}]' | jet --query '(count)'
2

echo '[{:a 1} {:a 2}]' | jet --query '(map count)'
[1 1]

Use juxt to apply multiple queries to the same element. The result is a list of multiple results.

$ echo '{:a [1 2 3] :b [4 5 6]}' | jet --query '(juxt :a :b)'
[[1 2 3] [4 5 6]]

$ echo '{:a [1 2 3]}' | jet --query '(update :a (juxt first last))'
{:a [1 3]}

$ echo '[1 2 3]' | jet --query '(juxt 0 1 2 3)'
[1 2 3 nil]

An example with zipmap:

$ echo '{:keys [:a :b :c] :vals [1 2 3]}' \
| jet --query '[(juxt :keys :vals) (zipmap)]'
{:a 1, :b 2, :c 3}

Examples with filter and remove:

$ curl -s https://jsonplaceholder.typicode.com/todos \
| jet --from json --keywordize --to edn --query '[(filter :completed) (count)]'
90

$ curl -s https://jsonplaceholder.typicode.com/todos \
| jet --from json --keywordize --to edn --query '[(remove :completed) (count)]'
110

Remove duplicate values with distinct and dedupe:

$ echo '{:a [1 1 2 2 3 3 1 1]}' | jet --query '[:a (distinct)]'
[1 2 3]

$ echo '{:a [1 1 2 2 3 3 1 1]}' | jet --query '[:a (dedupe)]'
[1 2 3 1]

Producing a string can be done with str:

 echo '{:a 1 :b 2}' | jet --query '(str :a #jet/lit "/" :b)'
"1/2"

Comparing values can be done with =, not=, >, >=, < and <=.

$ echo '[{:a 1} {:a 2} {:a 3}]' | jet --query '(filter (>= :a #jet/lit 2))'
[{:a 2} {:a 3}]

echo '[{:a {:b 1}} {:a {:b 2}}]' \
| jet --query '(filter (= [:a :b] #jet/lit 1))'
[{:a {:b 1}}]

Applying a regex can be done with re-find:

$ echo '{:a "foo bar" :b 2}' | lein jet --query '(re-find #jet/lit "foo" :a)'
"foo"

Control flow with if:

$ echo '{:a "foo bar" :b 2}' | jet --query '(if (re-find #jet/lit "foo" :a) :a :b)'
"foo bar"

There is also while, which repeats a query until the condition is not met.

$ echo '0' | jet --query '(while (< id #jet/lit 10) (inc id))'
10

The Fibonacci sequence using while:

$ echo '{:fib0 0 :fib1 1 :n 0 :fib []}' | lein jet --query '
(while (<= :n #jet/lit 10)
 {:fib0 :fib1 :fib1 (+ :fib0 :fib1) :n (inc :n) :fib (conj :fib :fib0)})
:fib'
[0 1 1 2 3 5 8 13 21 34 55]

Boolean logic:

$ echo '{:a 1 :b 3}' | jet --query '(and :a :b)'
3

$ echo '{:a 1 :b 3}' | jet --query '(or :a :b)'
1

$ echo '{:a 1 :b 3}' | jet --query '(not :a)'
false

Arithmetic:

$ echo '{:a 3 :b 2}]' | jet --query '(inc :a)'
4

$ echo '{:a 3 :b 2}]' | jet --query '(* :a :b) (- id #jet/lit 2)'
4

Use conj for adding elements to a list:

$ echo '[1 2 3]' | jet --query '(conj id #jet/lit 4)'
[1 2 3 4]

Because conj is varargs, it always takes an explicit input query.

Concatenating two lists or merging two maps can be done with into:

$ echo '{:a [1 2 3] :b [4 5 6]}' | jet --query '(into :a :b)'
[1 2 3 4 5 6]
$ echo '{:a {:x 1} :b {:y 2}}' | jet --query '(into :a :b)'
{:x 1, :y 2}

Gallery

jq example

The last example of the jq tutorial using jet:

$ curl -s 'https://api.github.com/repos/stedolan/jq/commits?per_page=5' | \
jet --from json --keywordize --to edn --pretty --query '
(map
 {:message [:commit :message]
  :name [:commit :committer :name]
  :parents [:parents (map :html_url)]})'

({:message "Merge pull request #1948 from eli-schwartz/no-pacman-sy\n\ndocs: fix seriously dangerous download instructions for Arch Linux",
  :name "GitHub",
...

Latest commit SHA

Get the latest commit SHA and date for a project from Github:

$ curl -s https://api.github.com/repos/borkdude/clj-kondo/commits \
| jet --from json --keywordize --to edn \
--query '[0 {:sha :sha :date [:commit :author :date]}]'
{:sha "bde8b1cbacb2b44ad2cd57d5875338f0926c8c0b", :date "2019-08-05T21:11:56Z"}

Find unused private vars using clj-kondo analysis output

cat << EOF > /tmp/test.clj
(ns foo)
(defn- foo []) ;; NOTE: unused
(defn- bar []) ;; NOTE: unused
(defn- baz [])

(defn -main []
  (baz))
EOF

clj-kondo --lint /tmp/test.clj --config '{:output {:analysis true :format :edn}}' | \
jet --query '
;; select the analysis part of the clj-kondo output
:analysis

;; create a map with private vars and used vars
{:private-vars [:var-definitions (filter :private) (map (select-keys [:name :ns]))]
 :used-vars [:var-usages (map [(select-keys [:name :to]) (set/rename-keys {:to :ns})])]}

;; private vars that are not used:
(set/difference :private-vars :used-vars)
'
#{{:name bar, :ns foo} {:name foo, :ns foo}}