jq_playground

Repo for playing around with jq.

Basics

Note

This README.md outputs to files so that you can see the output without having to run the queries yourself. If no output file is specified jq will output to the console.

From local file

big.json contains the last 1000 commits to the jq repo.

jq '.' < big.json > big_copy.json.

'.' formats the json.
< big.json big.json as input.
> big_copy.json writes to big_copy.json.

From pipe (cURL)

small.json contains the last 5 commits to the jq repo.

curl 'https://api.github.com/repos/jqlang/jq/commits?per_page=10 | jq '.' > small.json

curl X | jq pipes the output of curl to jq
'.' formats the json.
> small.json writes to small.json

Compact the JSON

Use the flag -c

jq '.' -c < big.json

See compacted.json for result.

Construct new structure from existing JSON

Each line = value of a field

You can use pipe within the jq-filter!

jq '.[] | .commit.message' < big.json

'' jq-filter is contained in quotes
.[] selects the entire array
| pipes the array to the next part of the jq-filter
.commit.message format of output; each line is set to the value of [x].commit.message

Alternative syntax: jq '.[].commit.message < big.json.

See messages for result.

Valid JSON

Note

If you'd like to output a valid JSON-array, you will have to construct a different output in the jq-filter:

jq '[.[] | {message: .commit.message}]' < big.json

Wrapping the entire filter in [] will output a JSON-array
Then you pipe the array (.[])
And you construct the new structure {message: .commit.message}, so that each entry in the array has that format.

See valid_messages.json for result.

Filter queries

You can also query the JSON through the filter.

Say we want every commit where the authors name is shorter than 7 characters

jq '.[] | select(.commit.author.name | length < 7)' < big.json (short_names.json)

Or every commit where the authors name contains Nico

jq '.[] | select(.commit.author.name | ascii_downcase | contains("nico"))' < big.json (nico.json)

Or commits where the authors name is shorter than 7 characters AND contains an e

jq '.[] | select((.commit.author.name | length < 7) and (.commit.author.name | ascii_downcase | contains("e")))' < big.json (short_e.json)

Handling "invalid" JSON

You can still often format and query JSON that's "invalid".

Format

jq -c '.[] | {message: .commit.message}' < big.json | jq '.'

The first jq command creates a compacted output where each line is {"message": "example"}
The second formats it. Output found in prettified_invalid.

Filter

jq '.[] | {message: .commit.message, sha: .sha}' < big.json | jq '.sha'

The first jq command creates a compacted output where each line is {"message": "example", "sha": "123afb"}
The second selects all values from the sha-field. Output in shas_from_invalid.

List all keys

jq '.[] | keys' < big.json

Will output all top-level keys. Output in outputs/all_keys

bjornevik/jq_playground