jsq

jsq is a tool for evaluating a JavaScript function and printing the result.

Help

Evaluate a JavaScript function and print the result

Usage: jsq [OPTIONS] [BODY]

Arguments:
  [BODY]  The body of the JavaScript function to be evaluated [default: $]

Options:
  -j, --json-in   Parse input as JSON
  -y, --yaml-in   Parse input as YAML
  -t, --toml-in   Parse input as TOML
  -J, --json-out  Print output as JSON
  -Y, --yaml-out  Print output as YAML
  -T, --toml-out  Print output as TOML
  -h, --help      Print help
  -V, --version   Print version

Input is avaialable in BODY as $. Environment variables are available in BODY prefixed by $.

Example

Suppose we have some JSON which contains a bunch of superheros and we want to find the hero with the power of "Immortality":

> curl https://mdn.github.io/learning-area/javascript/oojs/json/superheroes.json |
    jsq -jJ '$.members.find(m => m.powers.includes("Immortality"))'
{
  "name": "Eternal Flame",
  "age": 1000000,
  "secretIdentity": "Unknown",
  "powers": [
    "Immortality",
    "Heat Immunity",
    "Inferno",
    "Teleportation",
    "Interdimensional travel"
  ]
}

Semantics

The provided BODY is evaluated by Boa as part of the expression (() => BODY)(). In particular, this means that BODY must have the syntax of an Arrow Function body: it can either be a single expression, or multiple statements enclosed in braces with an explicit return.

$ contains the result of reading STDIN as text, or of parsing it as JSON if the -j flag is set, YAML if the -y flag is set, or TOML if the -t flag is set. If STDIN is a terminal then $ is the empty string.

The result is printed to STDOUT after being cast to a string, or serialized as JSON if the -J flag is set, YAML if the -Y flag is set, or TOML if the -T flag is set.

Environment variables are available in BODY prefixed by $. e.g. USER is available as $USER.

Why?

JavaScript is a convenient language with which to process JSON (which stands for "JavaScript Object Notation" after all), but the boilerplate of reading from STDIN, parsing, and writing to STDOUT makes many could-be "one-liners" significantly more involved than they need to be. jsq provides a thin wrapper around Boa which handles this boilerplate and makes it more ergonomic to sprinkle a little JavaScript in to a shell script.

jsq can be used for many of the same tasks as jq. A given jq command is often a little shorter than the equivalent jsq command, but if (like the author) you find yourself often forgetting the syntax of jq, and you already know JavaScript, you might find jsq easier to use. To see how jsq compares to jq, check out the translated jq tutorial.

Built-in functions

As well as the usual built-in functions provided by the engine, the following are available:

• YAML.parse – like JSON.parse but for YAML
• YAML.stringify – like JSON.stringify but for YAML
• TOML.parse – like JSON.parse but for TOML
• TOML.stringify – like JSON.stringify but for TOML

Install

With brew:

brew install callum-oakley/tap/jsq

With cargo:

cargo install jsq

Alternatively, there are binaries for Linux, MacOS, and Windows attached to each release.