Check if element is member of array [duplicate] - 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:
{
"fruit": [
"apple",
"orange",
"pomegranate",
"apricot",
"mango"
]
}
cat fruit.json | jq '.fruit .apple'
does not work

Answer 1

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" )
However, if the item of interest is itself an array, the general form:
ARRAY | index( [ITEM] )
should be used, e.g.:
[1, [2], 3] | index( [[2]] ) #=> 1
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;
any(_;_)
Another efficient alternative that is sometimes more convenient is to use any/2, e.g.
any(.fruit[]; . == "orange")
or equivalently:
any(.fruit[] == "orange"; .)

Answer 2

To have jq return success if the array fruit contains "apple", and error otherwise:
jq -e '.fruit|any(. == "apple")' fruit.json >/dev/null
To output the element(s) found, change to
jq -e '.fruit[]|select(. == "apple")' fruit.json
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 3

[WARNING: SEE THE COMMENTS AND ALTERNATIVE ANSWERS.]
cat fruit.json | jq '.fruit | contains(["orange"])'

Answer 4

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 5

Expanding on the answers here, If you need to filter the array of fruit against another array of fruit, you could do something like this:
cat food.json | jq '[.fruit[] as $fruits | (["banana", "apple"] | contains([$fruits])) as $results | $fruits | select($results)]'
This will return an array only containing "apple" in the above sample json.

Answer 6

This modified sample did worked here:
jq -r '.fruit | index( "orange" )' fruit.json | tail -n 1
It gets only the last line of the output.
If it exist, it returns 0.
If don't, it returns null.