Filter empty and/or null values with jq

user_2326896 0
Viewed 24538

I have a file with jsonlines and would like to find empty values.

{"name": "Color TV", "price": "1200", "available": ""}
{"name": "DVD player", "price": "200", "color": null}

And would like to output empty and/or null values and their keys:

available: ""
color: null

I think it should be something like cat myexample | jq '. | select(. == "")', but is not working.

jsonlines jq key-value null json
3 Answers

The tricky part here is emitting the keys without quotation marks in a way that the empty string is shown with quotation marks. Here is one solution that works with jq's -r command-line option:

to_entries[]
| select(.value | . == null or . == "")
| if .value == "" then .value |= "\"\(.)\"" else . end
| "\(.key): \(.value)"

Once the given input has been modified in the obvious way to make it valid JSON, the output is exactly as specified.

user_9973580

Some people may find the following jq program more useful for identifying keys with null or empty string values:

with_entries(select(.value |.==null or . == ""))

With the sample input, this program would produce:

{"available":""}
{"color":null}

Adding further information, such as the input line or object number, would also make sense, e.g. perhaps:

with_entries(select(.value |.==null or . == ""))
| select(length>0)
| {n: input_line_number} + .
user_9973580

With a single with_entries(if .value == null or .value == " then empty else . end) filter expression it's possible to filter out null and empty ("") values.

Without filtering:

echo '{"foo": null, "bar": ""}' | jq '.'
{
  "foo": null,
  "bar": ""
}

With filtering:

s3 echo '{"foo": null, "bar": ""}' |  jq 'with_entries(if .value == null or .value == "" then empty else . end)'
{}
user_21857190
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