Fetching a JSON file

Fetching a JSON file is the job of curl or similar tools. Here is an example how you might do it:

curl -X GET -H "Content-Type: application/json" -H "Authorization: Bearer $DO_API_TOKEN" "https://api.digitalocean.com/v2/images?type=distribution" > images.json

A few jq command that can be used for that file.

jq keys images.json

jq .images[].slug images.json

jq .links images.json  | jq keys

jq .images images.json  | jq keys      are all numbers

A sample JSON file

examples/data/in.json

{"prereqs":{"runtime":{"requires":{"Code::Explain":"0.02","App::Ack":"0","Archive::Any":"0","Acme::MetaSyntactic":"1.012"}}},"name":"Perl-Maven","author":["Gabor Szabo"],"abstract":"Web application running the Perl Maven sites","no_index":{"directory":["t","inc"]},"generated_by":"ExtUtils::MakeMaker version 7.08, CPAN::Meta::Converter version 2.150005","meta-spec":{"url":"http://search.cpan.org/perldoc?CPAN::Meta::Spec","version":"2"}}

Print the whole content of the JSON file in a readable way:

jq . in.json

Print the top-level keys of the file:

jq keys in.json

[
  "abstract",
  "author",
  "generated_by",
  "meta-spec",
  "name",
  "no_index",
  "prereqs"
]

The value of a key

The name after the dot.

jq .abstract examples/data/in.json
jq .prereqs examples/data/in.json

jq .prereqs.runtime.requires examples/data/in.json
{
  "Code::Explain": "0.02",
  "App::Ack": "0",
  "Archive::Any": "0",
  "Acme::MetaSyntactic": "1.012"
}

Element in a list

jq .no_index.directory[0] examples/data/in.json

Array as the top level item

If the top level is an array jq keys data.json will list the indexes jq .[0].name data.json will fetch the "name" field of the first element.

Generating JSON

echo '{}' | jq --arg name 'Foo Bar' --arg email 'foo@bar.com' '.name |= $name | .address |= $email'

generates this:

{
  "name": "Foo Bar",
  "address": "foo@bar.com"
}

Adding values to JSON

Given a JSON file, eg. template.json with the following content:

{
    "title": "Example"
}

We can add fields to it:

jq --arg name 'Foo Bar' --arg email 'foo@bar.com' '.name |= $name | .address |= $email' template.json 

The result will look like this:

{
  "title": "Example",
  "name": "Foo Bar",
  "address": "foo@bar.com"
}