Filtering JSON using jq with a condition-CodePudding

I have the following JSON:

{
  "LaunchTemplates": [
    {
      "LaunchTemplateName": "bla-99",
      "CreateTime": "2022-12-13T13:40:33 00:00"
    },
    {
      "LaunchTemplateName": "abcabc",
      "CreateTime": "2022-12-13T09:58:14 00:00"
    },
    {
      "LaunchTemplateName": "bla-34",
      "CreateTime": "2022-12-13T13:58:56 00:00"
    },
    {
      "LaunchTemplateName": "bla-222",
      "CreateTime": "2022-12-11T13:58:56 00:00"
    },
    {
      "LaunchTemplateName": "bla-233",
      "CreateTime": "2022-12-10T13:58:56 00:00"
    }
  ]
}

I want to filter the JSON and print the oldest templates after filtering. I have the following jq query that prints the template names after filtering:

file.json | jq  '.LaunchTemplates[].LaunchTemplateName|select(startswith("bla"))'

Output:

bla-99
bla-34
bla-222
bla-233

Now i want to add more logic to the query, and do something like that: If the number of bla lines is bigger than 3, then print the oldest bla lines (according to the date field). In my case, the output should be:

bla-233

Is that possible with jq or other shell commands? If so, how?

CodePudding user response：

If you are only interested in the last two elements (and ignoring the fact that the input in the question is invalid JSON):

.LaunchTemplates
| sort_by(.CreateTime)
| map(.LaunchTemplateName|select(startswith("")))[:-3]
| reverse[]

sort_by(.CreateTime) sorts ascending by the CreateTime property.
map(.LaunchTemplateName|select(startswith("bla")) maps the input array to an array containing only the template names with a "bla" prefix.
[:-3] slices the input array to drop the last 3 elements (i.e. dropping the 3 newest elements.
reverse[] reverses the array and streams its elements.

Output:

"bla-222"
"bla-233"