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' |