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Generating a JSON map containing shell variables named in a list.md

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Query: Generating a JSON map containing shell variables named in a list

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My shell-fu is at a below-beginner level. I have a file that contains some lines that happen to be the names of environment variables.

e.g.

ENV_VAR_A
ENV_VAR_B
...

What I want to do is use this file to generate a JSON string containing the names and current values of the named variables using jq like this:

jq -n --arg arg1 "$ENV_VAR_A" --arg arg2 "$ENV_VAR_B" '{ENV_VAR_A:$arg1,ENV_VAR_B:$arg2}'

# if ENV_VAR_A=one and ENV_VAR_B=two then the preceding command would output 
# {"ENV_VAR_A":"one","ENV_VAR_B":"two"}

I'm trying to create the jq command through a shell script and I have no idea what I'm doing :(

A:

jtc being a JSON utility, accepts as input only in JSON form, while the requestor's input file is clearly not the one. With jtc then it's required first to transform input into a stream of JSONs, which is easy:

bash $ <tmp.txt sed -E 's/(.*)/{"\1": 0}/' 
{"ENV_VAR_A": 0}
{"ENV_VAR_B": 0}
{"ENV_VAR_C": 0}
bash $

and once converted, jtc solution to transform it into the desired format:

bash $ export ENV_VAR_A='first token'
bash $ export ENV_VAR_B='2nd token'
bash $ 
bash $ <tmp.txt sed -E 's/(.*)/{"\1": 0}/' | jtc -Jw'[0]<L>k' -eu echo '\""${L}"\"' \; / -w[:][0] -ljj
{
   "ENV_VAR_A": "first token",
   "ENV_VAR_B": "2nd token",
   "ENV_VAR_C": ""
}
bash $

Explanation:

  • the first option-set jtc -Jw'[0]<L>k' -eu echo '\""${L}"\"' \;: memorizes the label of the input JSON (which is env. var) and updates the value with the shell-evaluated output for the given variable (combining all the processed outputs in one JSON array):
bash $ <tmp.txt sed -E 's/(.*)/{"\1": 0}/' | jtc -Jw'[0]<L>k' -eu echo '\""${L}"\"' \; 
[
   {
      "ENV_VAR_A": "first token"
   },
   {
      "ENV_VAR_B": "2nd token"
   },
   {
      "ENV_VAR_C": ""
   }
]
bash $
  • the second one -w[:][0] -ljj: walks each object's value ([:][0]) and join them together by labels (-l) into a JSON object (-jj)