Wednesday, 27 January 2021

More about jq - this time it's searching for stuff

 Having written a lot about jq recently, I'm continuing to have fun.

Today it's about searching for stuff, as I was seeking to parse a huge amount of output ( a list of running containers ) for a snippet of the container's name ....

Here's an example of how I solved it ...

Take an example JSON document: -

cat family.json 

{
    "friends": [
        {
            "givenName": "Dave",
            "familyName": "Hay"
        },
        {
            "givenName": "Homer",
            "familyName": "Simpson"
        },
        {
            "givenName": "Marge",
            "familyName": "Simpson"
        },
        {
            "givenName": "Lisa",
            "familyName": "Simpson"
        },
        {
            "givenName": "Bart",
            "familyName": "Simpson"
        }
    ]
}

I can then use jq to dump out the entire document: -

cat family.json | jq

{
  "friends": [
    {
      "givenName": "Dave",
      "familyName": "Hay"
    },
    {
      "givenName": "Homer",
      "familyName": "Simpson"
    },
    {
      "givenName": "Marge",
      "familyName": "Simpson"
    },
    {
      "givenName": "Lisa",
      "familyName": "Simpson"
    },
    {
      "givenName": "Bart",
      "familyName": "Simpson"
    }
  ]
}

but, say, I want to find all the records where the familyName is Simpson ?

cat family.json | jq -c '.friends[] | select(.familyName | contains("Simpson"))'

{"givenName":"Homer","familyName":"Simpson"}
{"givenName":"Marge","familyName":"Simpson"}
{"givenName":"Lisa","familyName":"Simpson"}
{"givenName":"Bart","familyName":"Simpson"}

or all the records where the givenName contains the letter a ?

cat family.json | jq -c '.friends[] | select(.givenName | contains("a"))'

{"givenName":"Dave","familyName":"Hay"}
{"givenName":"Marge","familyName":"Simpson"}
{"givenName":"Lisa","familyName":"Simpson"}
{"givenName":"Bart","familyName":"Simpson"}

or, as an edge-case, where the givenName contains the letter A or the letter a i.e. ignore the case ?

cat family.json | jq -c '.friends[] | select(.givenName | match("A";"i"))'

{"givenName":"Dave","familyName":"Hay"}
{"givenName":"Marge","familyName":"Simpson"}
{"givenName":"Lisa","familyName":"Simpson"}
{"givenName":"Bart","familyName":"Simpson"}

TL;DR; jq rules!

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