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200ok - Consultancy, Research Lab, Incubator

Frustration with slow and manual processes is probably my number one motivator to discover new tooling. Having lately worked with Swagger on a Json API I found myself in need of a tool to work with Json on the command line.

I tried a couple and just when I was about to make the decision that I want to try them all to find the best one my search was cut short when I tried jq. On the web site it claims: jq is like sed for JSON data. And come to think of it what would we do without sed?

And yes, it's that good. Here two easy examples:

Extracting a field

Let's say you access an API to retrieve an access key. Then that's what it probably looks like.

curl -s -X PUT --header 'Content-Type: application/json' \
  --header 'Accept: application/json' \
  -d '{
    "email": "your@email.address",
    "password": "swaggerrocks"
    }' \
  'https://your.api.endpoint/'

This of course will return a whole Json object.

{"access":"1234567890987654321", "some":"more", "fields":"you don't care about"}

But you might only be interested in the access key. Pipe it through jq.

curl -s -X PUT --header 'Content-Type: application/json' \
  --header 'Accept: application/json' \
  -d '{
    "email": "your@email.address",
    "password": "swaggerrocks"
    }' \
  'https://your.api.endpoint/' | jq -r .access

This will print

1234567890987654321

(Which in my setup is then piped into xclip -i to copy it to X's primary clipboard.) The -r switch gives you the raw output instead of surrounding the resulting string with quotes.

jq comes with its own mini language to define "filters" (more like transformers) to manipulate Json or extract data out of it.

Since I now have a tool at hand to work with Json on the command line nicely. It suddenly bothers me that I've to pass carefully crafted literal Json into the curl earlier. Hence in a second example I will show how to use jq to generate Json.

Generate Json

To generate Json we tell jq with the -n switch to expect no input. We'll then use filters to add our data.

jq -n '.email="your@email.address"|.password="swaggerrocks"'

Using this technique we can refactor our command from earlier to

jq -n '.email="your@email.address"|.password="swaggerrocks"' \
  | curl -s -X PUT -d @- \
  --header 'Content-Type: application/json' \
  --header 'Accept: application/json' \
  'https://your.api.endpoint/' \
  | jq -r .access

I find some beauty in that.

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