json - 使用 jq 从 json 流中进行第一次匹配

Question

为什么 first(select(.updated_at=="2019-06-03T16:36:53.194Z")) 在输入时返回超过 1 个结果

{"_id":"a","updated_at":"2019-06-03T16:36:53.194Z"}
{"_id":"b","updated_at":"2019-06-03T19:27:15.192Z"}
{"_id":"c","updated_at":"2019-06-03T20:02:11.538Z"}
{"_id":"d","updated_at":"2019-06-03T21:12:05.764Z"}
{"_id":"e","updated_at":"2019-06-04T07:55:04.251Z"}
{"_id":"f","updated_at":"2019-06-03T22:21:37.276Z"}
{"_id":"g","updated_at":"2019-06-03T20:57:42.296Z"}
{"_id":"h","updated_at":"2019-06-03T18:56:07.687Z"}
{"_id":"i","updated_at":"2019-06-04T09:28:08.276Z"}
{"_id":"j","updated_at":"2019-06-04T08:54:05.048Z"}
{"_id":"k","updated_at":"2019-06-03T16:36:53.194Z"}
{"_id":"l","updated_at":"2019-06-03T16:36:53.194Z"}

https://jqplay.org/s/2sm1pKQ2fS

我也尝试过使用 nth 但它似乎也没有预期的行为:

https://jqplay.org/s/DeSANQZtj7

Answer 1

因为，first 的输入是一个对象流，因此它为每个对象运行一次。要为整个流运行一次，请在命令行上指定 -n/--null-input 标志，并使用 inputs 函数访问输入。这样，first 的输入将为 null，其参数将为从 inputsselect 的对象流, 所以它只能产生第一个。

$ jq -n 'first(inputs | select(.updated_at == "2019-06-03T16:36:53.194Z"))' file
{
  "_id": "a",
  "updated_at": "2019-06-03T16:36:53.194Z"
}