gron. A json grepper.

gron is a brew installable tool that works on json data. Particularly useful to extract key:value from large json documents. Essentially gron flattens the json. This is surprisingly useful when creating shell tools that have to deal with json.

gron basic use

pipe that json into gron

garymbp:~ gary$ curl -S -u "$username:$password" -k -X GET --header 'Accept: application/json' $URL 2>/dev/null | gron | tail
json.metadata = {};
json.metadata.count = 1;
json.metadata.end_index = 1;
json.metadata.filter_criteria = "";
json.metadata.grand_total_entities = 5;
json.metadata.page = 1;
json.metadata.search_string = "ctr1";
json.metadata.sort_criteria = "";
json.metadata.start_index = 1;
json.metadata.total_entities = 1;

Extract fields from an API call with gron and grep

For instance let’s say we want to see all the json fields that contain the word iops regardless of where it appears in the structure. We can simply pipe the json into gron then into grep like we have always done.

garymbp:~ gary$ curl -S -u "$username:$password" -k -X GET --header 'Accept: application/json' $URL 2>/dev/null | gron | grep iops
json.entities[0].stats.controller_num_iops = "65066";
json.entities[0].stats.controller_num_read_iops = "39096";
json.entities[0].stats.controller_num_write_iops = "25969";
json.entities[0].stats.hypervisor_num_iops = "-1";
json.entities[0].stats.hypervisor_num_read_iops = "-1";
json.entities[0].stats.hypervisor_num_write_iops = "-1";
json.entities[0].stats.num_iops = "-1";
json.entities[0].stats.num_read_iops = "-1";
json.entities[0].stats.num_write_iops = "-1";

gron and jq

Using the output from gron we can now easily figure out what we need to feed into jq to get the field we want without having to parse the json structure too much. Most of the time just remove the word json from the front then put the res in single quotes and pass to jq. So in the case we want controller_num_iops we know that we need to feed jq the full query .entities[0].stats.controller_num_iops to jq and we get our answer ""65066""

garymbp:~ gary$ curl -S -u "$username:$password" -k -X GET --header 'Accept: application/json' $URL 2>/dev/null | jq '.entities[0].stats.controller_num_iops'
"65066"