jq & bash: make JSON array from variable

Question

I'm using jq to form a JSON in bash from variable values.

Got how to make plain variables

$ VAR="one two three"
$ jq -n "{var:\"$VAR\"}"
{
  "var": "one two three"
}

But can't make arrays yet. I have

$ echo $ARR
one
two
three

and want to get something like

{
  "arr": ["one", "two", "three"]
}

I only manage to get garbled output like

$ jq -n "{arr: [\"$ARR\"]}"
{
  "arr": [
    "one\ntwo\nthree"
  ]
}

How to form JSON array in a correct way? Can jq ever do that?

EDIT: Question was asked when there was only jq 1.3. Now, in jq 1.4, it is possible to do straightly what I asked for, like @JeffMercado and @peak suggested, upvote for them. Won't undo acceptance of @jbr 's answer though.

Answer 1

jq is doing exactly what you tell it to do. jq is not a program for generating JSON, but a tool for querying it. What you are doing with the -n switch is just using it as a pretty printer. So if you want it to print an object with an array containing "one", "two", "three" then you have to generate it.

VAR="one two three"
VAR=$(echo $VAR | sed -e 's/\(\w*\)/,"\1"/g' | cut -d , -f 2-)
echo "{var: [$VAR]}"

Update

As Bryan and others mention below it is indeed possible to generate JSON with jq, and from version 1.4, it's even possible to do what the OP ask directly, see for example Jeff's answer.

Answer 2

In jq 1.3 and up you can use the --arg VARIABLE VALUE command-line option:

jq -n --arg v "$VAR" '{"foo": $v}'

I.e., --arg sets a variable to the given value so you can then use $varname in your jq program, and now you don't have to use shell variable interpolation into your jq program.

EDIT: From jq 1.5 and up, you can use --argjson to pass in an array directly, e.g.

jq -n --argjson v '[1,2,3]' '{"foo": $v}'

Answer 3

Once you have your variable loaded, you should use the split filter to split that string into an array.

$ jq -n --arg inarr "${ARR}" '{ arr: $inarr | split("\n") }'

Answer 4

The original posting in this thread mentions VAR="one two three". For such a variable, a very simple solution in jq 1.4 is as follows:

$ jq -n -c -M --arg s "$VAR" '{var: ($s|split(" "))}'
{"var":["one","two","three"]}

(This assumes a Linux or Mac shell or similar, and works with jq 1.4.)

If the separator character is a newline, then consider this typescript:

$ s=$(printf "a\nb\nc\n")
$ jq -n -c -M --arg var "$s" '{"var": ($var|split("\n"))}'
{"var":["a","b","c"]}

Notice that the JSON string for the newline character is "\n" (not "\\n").

A third case of interest is when VAR is a bash array. In this case, it may be acceptable to pass in the items using "${VAR[@]}", but in general, it must be remembered that the "--arg name value" option is intended only for passing in strings.

In jq>1.4, exported shell variables can be passed in using the "env" object, as documented in the online jq manual page.

Answer 5

This worked for me in jq 1.6:

$ jq -nc '$ARGS.positional' --args 1 2 3
["1","2","3"]

For this specific use-case, you could use an array and write:

$ VAR=(one two three)
$ jq -nc '{var: $ARGS.positional}' --args ${VAR[@]}
{"var":["one","two","three"]}

You could also use a string like this:

$ VAR="one two three"
$ jq -nc '{var: ($ARGS.positional[0] | split(" "))}' --args $VAR

Answer 6

First you have to use -R to read the raw lines and next you have to slurp all values with -s:

$ echo -e "one\ntwo\nthree" | jq -R . | jq -s '{"arr": .}'
{
  "arr": [
    "one",
    "two",
    "three"
  ]
}