jq --slurp

1 minute read Published: 2022-08-18

jq --slurp conflates multiple JSON document inputs into a single array. This allows you to run a jq filter only once for all inputs, instead of once per document.

jq can transform JSON in various ways, by selecting, iterating, reducing and otherwise mangling JSON documents. For instance, running the command jq 'map(.price) | add' will take an array of JSON objects as input and return the sum of their "price" fields.

By default, it'll take a single JSON document as input, but with the --slurp option you can tell jq to read the entire input and put it in an array, allowing you to parse multiple JSON documents in one go.

This is extraordinarily useful for files that contain a distinct JSON object per line, for example a log file:

$ cat log.txt
{"id": 1, "log": { "message": "Some Log Message Here!", "level": "INFO" }}
{"id": 2, "log": { "message": "More messages!", "level": "WARN" }}
{"id": 3, "log": { "message": "Something went wrong!", "level": "ERROR" }}

$ jq --slurp '.[].id' log.txt

$ jq --slurp 'map(select(.log.level == "ERROR") | .log.message)' log.txt
    "Something went wrong!"