JSON JQ(如果没有其他条件) [英] JSON JQ if without else

问题描述

我使用以下JQ命令来过滤JSON.我的要求是，如果存在预期的节点，则过滤掉JSON消息.否则，什么都不做.因此，我使用if，elif，....

I use the following JQ command to filter out the JSON. My requirement is to filter out the JSON message if the expected node is present. Or else, do nothing. Hence, I use if, elif, ....

sed -n "s/.*Service - //p" $1/response.log* |
  jq "if (.requests | length) != 0 then .requests |= map(select(.id == \"123\"))
      elif (.result | length ) != 0  then .result |= map(select(.id== \"123\")) 
      else " "  end" > ~/result.log

在这里像其他一样是强制性的.我不想在else块内做任何事情.无论如何，我可以忽略其他内容，或者在其他内容中打印一些空白.

Looks like else is mandatory here. I dont want to do anything inside the else block. Is there anyway, I can ignore else or just print some whitespce inside else.

在上述情况下，它将在结果文件中打印双引号".

In the above case, it prints double quotes " " in the result file.

推荐答案

您可能想使用以下成语:

You may want to use the idiom:

if CONDITION then WHATEVER else empty end

empty是一个根本不输出任何内容的过滤器-甚至不为null，这毕竟是某种东西(即JSON值).它有点像一个黑洞，只是更黑了-它会消耗掉所提供的任何东西，但是与黑洞不同，它甚至不会发出霍金辐射.

empty is a filter that outputs nothing at all -- not even null, which is after all something (namely a JSON value). It's a bit like a black hole, only blacker -- it will consume whatever it's offered, but unlike a black hole, it does not even emit Hawking radiation.

在您的情况下，您有一个"elif"，因此您可能需要使用"else empty"，但作为参考，以上内容完全等同于:

In your case, you have an "elif" so using "else empty" is probably what you want, but for reference, the above is exactly equivalent to:

select(CONDITION) | WHATEVER

P.S.我的猜测是，无论sed命令的目标是什么，它都可以作为jq程序的一部分更可靠地完成，也许可以使用walk/1来完成.

P.S. My guess is that whatever the goal of the sed command, it could be done more reliably as part of the jq program, perhaps using walk/1.

在发布jq 1.6之后，进行了更改，以使"if if else else"的语义为"if _ then _ else.end"，即:

After the release of jq 1.6, a change was made so that "if without else" has the semantics of "if _ then _ else . end", that is:

if P then Q end === if P then Q else . end

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