How to check if element exists in array with jq

Question

I have an array and I need to check if elements exists in that array or to get that element from the array using jq, fruit.json:

{
    \"fr         


        

Answer 1

[WARNING: SEE THE COMMENTS AND ALTERNATIVE ANSWERS.]

cat fruit.json | jq '.fruit | contains(["orange"])'

Answer 2

For future visitors, if you happen to have the array in a variable and want to check the input against it, and you have jq 1.5 (without IN), your best option is index but with a second variable:

.inputField as $inputValue | $storedArray|index($inputValue)

This is functionally equivalent to .inputField | IN($storedArray[]).

Answer 3

To have jq return success if the array fruit contains "apple", and error otherwise:

jq -e '.fruit[]|select(. == "apple")' fruit.json >/dev/null

To output the element(s) found, omit >/dev/null. If searching for a fixed string, this isn't very relevant, but it might be if the select expression might match different values, e.g. if it's a regexp.

To output only distinct values, pass the results to unique.

jq '[.fruit[]|select(match("^app"))]|unique' fruit.json

will search for all fruits starting with app, and output unique values. (Note that the original expression had to be wrapped in [] in order to be passed to unique.)

Answer 4

If you're open to using something other than jq, then I can highly recommend Xidel.
With it you can combine JSONiq and XPath/XQuery to process JSON!

To have it simply return a boolean:

$ xidel -s fruit.json -e '$json/contains((fruit)(),"apple")'
true

To have it return the element if the array fruit contains "apple":

$ xidel -s fruit.json -e '$json/(fruit)()[contains(.,"apple")]'
apple

Above is "XPath notation". "Dot notation" (like jq):

$ xidel -s fruit.json -e '($json).fruit()[contains(.,"apple")]'
apple

Answer 5

The semantics of 'contains' is not straightforward at all. In general, it would be better to use 'index' to test if an array has a specific value, e.g.

.fruit | index( "orange" )

IN/1

If your jq has IN/1 then a better solution is to use it:

.fruit as $f | "orange" | IN($f[])

If your jq has first/1 (as does jq 1.5), then here is a fast definition of IN/1 to use:

def IN(s): first((s == .) // empty) // false;