JQ中的可选密钥

Question

输入内容(somejson.json(是

{ "m1": "1 some m1", "m2": null , "m3" : "unwanted"}
{ "m1": "2 some m1", "m3" : "unwanted"}
{ "m1": "3 some m1", "m2": "3 some m2" , "m3" : "unwanted"}
{ "m1": "4 some m1", "m3" : "unwanted"}

是否有提取的选项，例如M1。还要提取M2如果存在？

示例。对于M1，我使用以下命令

cat somejson.json |jq '.m1'

输出

"1 some m1"
"2 some m1"
"3 some m1"
"4 some m1"

对于M2，我使用以下命令

cat somejson.json |jq '.m2'

输出

null
null
"3 some m2"
null

，但我想要合并的结果，包括M1和M2，如下

"1 some m1"
"2 some m1"
"3 some m1"
"3 some m2"
"4 some m1"

Answer 1

获得两个值；如果不存在，它们将是null。然后只需从结果中过滤零。

<somejson.json jq '.m1, .m2 | select(. != null)'

Answer 2

始终提取m1：

jq '.m1, if (.m2 != null) then .m2 else empty end' somejson.json