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About json : how-to-parse-a-JSON-String-with-jq-or-other-alternatives

Question Detail

I’m trying to get jq to parse a JSON structure like:

  "a" : 1,
  "b" : 2,
  "c" : "{\"id\":\"9ee ...\",\"parent\":\"abc...\"}\n"

That is, an element in the JSON is a string with escaped json.

So, I have something along the lines of
$ jq [.c] myFile.json | jq [.id]

But that crashes with jq: error: Cannot index string with string

This is because the output of .c is a string, not more JSON.
How do I get jq to parse this string?

My initial solution is to use sed to replace all the escape chars (\":\", \",\" and \") but that’s messy, I assume there’s a way built into jq to do this?


Also, the jq version available here is:

$ jq --version
jq version 1.3

I guess I could update it if required.

Question Answer

jq has the fromjson builtin for this:

jq '.c | fromjson | .id' myFile.json

fromjson was added in version 1.4.

You can use the raw output (-r) that will unescape characters:

jq -r .c myfile.json | jq .id

ADDENDUM: This has the advantage that it works in jq 1.3 and up; indeed, it should work in every version of jq that has the -r option.

Motivation: you want to parse JSON string – you want to escape a JSON object that’s wrapped with quotes and represented as a String buffer, and convert it to a valid JSON object. For example:

some JSON unescaped string :

"{\"name\":\"John Doe\",\"position\":\"developer\"}"

the expected result ( a JSON object ):

{"name":"John Doe","position":"developer"}

Solution: In order to escape a JSON string and convert it into a valid JSON object use the sed tool in command line and use regex expressions to remove/replace specific characters:

cat current_json.txt | sed -e 's/\\\"/\"/g' -e 's/^.//g' -e 's/.$//g'

s/\\\"/\"/g replacing all backslashes and quotes ( \" ) into quotes only (")

s/^.//g replacing the first character in the stream to none character

s/.$//g replacing the last character in the stream to none character

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