jq - return json as bash array

To convert your JSON to a bash array, with help of jq:

$ readarray -t arr < <(jq '.value' file)
$ printf '%s\n' "${arr[@]}"
"1"
"3"
"4"

To fix your expanded example (the exact command), just don't use object construction {value: .Value}, but instead only .Value:

$ readarray -t arr < <(aws ec2 describe-instances --region=us-east-1 --filters --filters "Name=tag:NodeType,Values=worker" --query "Reservations[].Instances[].Tags[]" | jq -r '.[] | select(.Key == "NodeNumber") | .Value')
$ printf '%s\n' "${arr[@]}"
1
3
4

Notice the lack of double quotes, since the -r option now prints only raw string values, not raw JSON Objects.

After you get arr populated with values like this, you can easily iterate over it and perform tests, just as you described in your question.

First, Store the Data

Given your raw data stored as a string in a json variable, perhaps with a here-document:

json=$(
    cat <<- EOF
        {
          "value": "1"
        }
        {
          "value": "3"
        }
        {
          "value": "4"
        }
EOF
)

Bash itself will do a reasonable job of prettifying it:

$ echo $json
{ "value": "1" } { "value": "3" } { "value": "4" }

Parsing the Data Into a Bash Array

There's more than one way to do this. Two of the more obvious ways are to use use jq or grep to extract the values into a Bash array with the shell's simple array notation:

values=( `echo $json | jq .value` )
echo "${values[@]}"
"1" "3" "4"

unset values
values=$(egrep -o '[[:digit:]]+' <<< "$json")
echo "${values[@]}"
1
3
4

There are certainly other ways to accomplish this task, but this seems like the low-hanging fruit. Your mileage may vary.

Caveat

The main thing to remember about Bash arrays is that they need to use expansions such as "${foo[@]}" when quoted, or ${bar[*]} when unquoted, if you want to use them for loops rather than indexing into them directly. Once they're in an array, though, you can access the entire array easily as long as you understand the different expansions and quoting rules.

Using the "-s" command-line option of jq, the following meets the requirements as I understand them, while generalizing them as well:

map(.value | tonumber)
| unique
| (1+max - min) as $length
| if $length > length then ([range(min;max+1)] - .)[]
  else max+1
  end

If you just want the least missing value, then replace the '[]' on the 'if' line by [0],

This might give you some ideas:

#!/bin/bash

complete=true

while read value;do

    n=${n:-$value}

    if (( value != n ));then
            complete=false
            echo $n
            break
    fi

    let n++

done < <(jq -r '.value' json_file)
# or: done < <( command_that_outputs_json | jq -r '.value' )

$complete && echo $n