Convert bash array to json array and insert to file using jq

(1) If all the values in newArray are valid as JSON values without spaces, then you could get away with piping the values as a stream, e.g.

newArray=(100 200 300)
echo "${newArray[@]}" |
  jq -s '{client_nohup: ., server_nohup: []}'

(2) Now let's suppose you merely wish to update the "nohup" object in a file, say nohup.json:

{ "client_nohup": [], "server_nohup": [ "keep me" ] }

Since you are using bash, you can then write:

echo "${newArray[@]}" |
  jq -s --argjson nohup "$(cat nohup.json)" '
    . as $newArray | $nohup | .client_nohup = $newArray
  '

Output

(1)

{
  "client_nohup": [
    100,
    200,
    300
   ],
  "server_nohup": []
}

(2)

{
  "client_nohup": [
    100,
    200,
    300
  ],
  "server_nohup": [
    "keep me"
  ]
}

Other cases

Where there's a will, there's a jq way :-)

See for example the accepted answer at How to format a bash array as a JSON array (though this is not a completely generic solution).

For a generic solution, see 𝑸: How can a variable number of arguments be passed to jq? How can a bash array of values be passed in to jq as a single argument? at the jq FAQ https://github.com/stedolan/jq/wiki/FAQ

Generic Solutions

To be clear, if the array values are known to be valid JSON, there are several good options; if the array values are arbitrary bash strings, then the only efficient, generic way to handle them with jq is by using the -R jq option (e.g. in conjunction with -s), but then the (bash) strings will all be read in as JSON strings, so any intended type information will be lost. (The point here hinges on the technicality that bash strings cannot CONTAIN NUL characters.)

Often, to alleviate the latter concern, one can convert numeric strings to JSON numbers, e.g. using the jq idiom: (tonumber? // .).