How to to extract the year from JSON date using jq

Question

I have a bunch of JSON with dates in ISO format. How can I print only the year component of the date?

$ echo '{"createdDate": "2005-09-28T16:34:40Z"}' | jq '{ createdYear: ??? }'
{
  "createdYear": "2005"
}

Answer 1

Use strptime to convert date string to date object and then strftime to format the date:

$ echo '{"createdDate": "2005-09-28T16:34:40Z"}' |
    jq '
       { createdYear: .createdDate
           | strptime("%Y-%m-%dT%H:%M:%SZ")
           | strftime("%Y") }'
{
  "createdYear": "2005"
}

Answer 2

Why not just:

{createdYear: .createdDate[0:4]}