olih/jq-cheetsheet.md

## jq-cheetsheet.md

      
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              jq-cheetsheet.md
            
          
    Processing JSON using jq

jq is useful to slice, filter, map and transform structured json data.
Installing jq

On Mac OS

brew install jq
On AWS Linux

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.
Useful arguments

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.


Basic concepts

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


Dealing with json objects


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 &#124; map([.key, .value])


Dealing with fields


Description
Command


Concatenate two fields
fieldNew=.field1+' '+.field2


Dealing with json arrays

Slicing and Filtering


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


Mapping and Transforming


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'
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.
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
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'`