使用jq检查字符串是否是有效的JSON

问题描述

取消服务时，我需要捕捉一个错误.响应可以是null，类似

I need to catch an error when lifting a service. The response can be null, a string error message like

error services-migration/foobar: Not found: services-migration/foobar

或一切正常时的有效JSON.我想知道jq是否有一种方法可以简单地检查所提供的字符串是否为有效的JSON.我可以经常检查某些关键字的字符串，例如error f.e.，但是我正在寻找一个更可靠的选项，例如.我从jq得到true/false或1/0.我正在浏览jq的文档以及关于SO的一些问题，但所有内容都是关于从JSON查找和挑选键值的，但与简单地验证字符串无关.

or a valid JSON when everything is fine. I was wondering if there is a way with jq to simply check if the provided string is a valid JSON. I could ofc check the string for some keywords like error f.e., but I'm looking for a more robust option, where eg. I get a true/false or 1/0 from jq.I was looking through the docs of jq and also some questions here on SO but everything was about finding and picking out key-values from a JSON, but nothing about simply validating a string.

更新:

我有这个:

 result=$(some command)

的结果是字符串error services-migration/foobar: Not found: services-migration/foobar

然后是if语句:

 if jq -e . >/dev/null 2>&1 <<<"$result"; then
    echo "it catches it"
 else
    echo "it doesn't catch it"
 fi

它总是以else子句结尾.

推荐答案

摘自手册:

如果最后一个输出值既不是false也不是null，则将jq的退出状态设置为0；如果最后一个输出值是false或null则将jq的退出状态设置为1；或者，如果没有产生有效结果，则将其设置为4.通常，如果出现使用问题或系统错误，jq退出时为2；如果出现jq程序编译错误，则退出3；如果运行jq程序，则退出0.

Sets the exit status of jq to 0 if the last output values was neither false nor null, 1 if the last output value was either false or null, or 4 if no valid result was ever produced. Normally jq exits with 2 if there was any usage problem or system error, 3 if there was a jq program compile error, or 0 if the jq program ran.

因此您可以使用:

if jq -e . >/dev/null 2>&1 <<<"$json_string"; then
    echo "Parsed JSON successfully and got something other than false/null"
else
    echo "Failed to parse JSON, or got false/null"
fi

实际上，如果您不关心区分不同类型的错误，那么您可以丢掉-e开关.在这种情况下，筛选器.将成功解析任何被视为有效JSON(包括false/null)的内容，并且程序将成功终止，因此将遵循if分支.

In fact, if you don't care about distinguishing between the different types of error, then you can just lose the -e switch. In this case, anything considered to be valid JSON (including false/null) will be parsed successfully by the filter . and the program will terminate successfully, so the if branch will be followed.

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