jq is useful to slice, filter, map and transform structured json data.
brew install jq
Not available as yum install on our current AMI. It should be on the latest AMI though: https://aws.amazon.com/amazon-linux-ami/2015.09-release-notes/
Installing from the source proved to be tricky.
When running jq, the following arguments may become handy:
| Argument | Description |
|---|---|
--version |
Output the jq version and exit with zero. |
--sort-keys |
Output the fields of each object with the keys in sorted order. |
The syntax for jq is pretty coherent:
| Syntax | Description |
|---|---|
| , | Filters separated by a comma will produce multiple independent outputs |
| ? | Will ignores error if the type is unexpected |
| [] | Array construction |
| {} | Object construction |
| + | Concatenate or Add |
| - | Difference of sets or Substract |
| length | Size of selected element |
| | | Pipes are used to chain commands in a similar fashion than bash |
| Description | Command |
|---|---|
| Display all keys | jq 'keys' |
| Adds + 1 to all items | jq 'map_values(.+1)' |
| Delete a key | jq 'del(.foo)' |
| Convert an object to array | to_entries | map([.key, .value]) |
| Description | Command |
|---|---|
| Concatenate two fields | fieldNew=.field1+' '+.field2 |
| Description | Command |
|---|---|
| All | jq .[] |
| First | jq '.[0]' |
| Range | jq '.[2:4]' |
| First 3 | jq '.[:3]' |
| Last 2 | jq '.[-2:]' |
| Before Last | jq '.[-2]' |
| Select array of int by value | jq 'map(select(. >= 2))' |
| Select array of objects by value | ** jq '.[] | select(.id == "second")'** |
| Select by type | ** jq '.[] | numbers' ** with type been arrays, objects, iterables, booleans, numbers, normals, finites, strings, nulls, values, scalars |
| Description | Command |
|---|---|
| Add + 1 to all items | jq 'map(.+1)' |
| Delete 2 items | jq 'del(.[1, 2])' |
| Concatenate arrays | jq 'add' |
| Flatten an array | jq 'flatten' |
| Create a range of numbers | jq '[range(2;4)]' |
| Display the type of each item | jq 'map(type)' |
| Sort an array of basic type | jq 'sort' |
| Sort an array of objects | jq 'sort_by(.foo)' |
| Group by a key - opposite to flatten | jq 'group_by(.foo)' |
| Minimun value of an array | jq 'min' .See also min, max, min_by(path_exp), max_by(path_exp) |
| Remove duplicates | jq 'unique' or jq 'unique_by(.foo)' or jq 'unique_by(length)' |
| Reverse an array | jq 'reverse' |
@hgovindh86 how's this:
{ "msg": { "blockdevices": [ { "mountpoint": "/snap/core18/2246", "name": "loop0" }, { "mountpoint": "/snap/core18/2253", "name": "loop1" }, { "mountpoint": "/snap/core20/1169", "name": "loop2" }, { "mountpoint": "/snap/lxd/21803", "name": "loop3" }, { "mountpoint": "/snap/core20/1242", "name": "loop4" }, { "mountpoint": "/snap/lxd/21835", "name": "loop5" }, { "mountpoint": "/snap/snapd/14066", "name": "loop6" }, { "mountpoint": "/snap/snapd/13640", "name": "loop7" }, { "children": [ { "mountpoint": "/boot/efi", "name": "sda1" }, { "mountpoint": "/boot", "name": "sda2" }, { "children": [ { "children": [ { "mountpoint": "/", "name": "ubuntu--vg-ubuntu--lv" }, { "mountpoint": null, "name": "ubuntu--vg-clean" } ], "mountpoint": null, "name": "ubuntu--vg-ubuntu--lv-real" }, { "children": [ { "mountpoint": null, "name": "ubuntu--vg-clean" } ], "mountpoint": null, "name": "ubuntu--vg-clean-cow" } ], "mountpoint": null, "name": "sda3" } ], "mountpoint": null, "name": "sda" }, { "children": [ { "mountpoint": null, "name": "datavg-datavol1" } ], "mountpoint": null, "name": "sdb" } ] } }as foo.json
jq '.. | {m: .mountpoint?,name} | select(.m == "/") | .name' foo.json ubuntu--vg-ubuntu--lvThe result isn't what you say it should be, but based on independent inspection it's correct. If I grep for your results: