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jq Cheet Sheet

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 | 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'
@mirisu2
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mirisu2 commented Jul 17, 2022

I already tried on jqplay. The result is the same. :(

@jsmucr
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jsmucr commented Jul 17, 2022

@notorand-it
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notorand-it commented Oct 26, 2022

Puzzle: how do I go from this:

{
  "widgets": [
    {
      "name": "foo",
      "properties": [
        "baz"
      ]
    },
    {
      "name": "bar"
    }
  ]
}

to this

{
  "widgets": [
    {
      "name": "foo",
      "properties": [
        "baz",
        "boo"
      ]
    },
    {
      "name": "bar"
    }
  ]
}

Or, is it possible to I add an item into an internal array?

@jsmucr
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jsmucr commented Oct 31, 2022

@notorand-it Try this:

. as $root |
($root.widgets[] | select(.name != "foo")) as $others |
($root.widgets[] | select(.name == "foo") * { properties: (.properties + ["boo"])}) as $newfoo |
$root * { widgets: ([$newfoo] + [$others]) }

I'm pretty sure it can be done some more sophisticated way, but this works too and is easy to understand.

@twosider
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twosider commented Apr 13, 2023

Puzzle: how do I go from this:

{ "widgets": [ ...
  "properties":["baz"]
  ...

to this

{ "widgets": [...
   "properties": ["baz","boo"]
...

Or, is it possible to I add an item into an internal array?

This is a good one to understand how jq can manipulate an object directly:

jq '.widgets[0].properties += ["boo"]'

This works because adding an array to another array concatenates the elements:

jq -cn '[1]+[2]'
[1,2]
jq -cn '["baz"]+["boo"]'
["baz","boo"]

@tmprender
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Hoping I found the right place... I've been trying to figure out if there's a way to use jq in order to "flatten" nested json into simple dot-delimited "path.to.key=value" lines.

For example, given the following input:

user@shell:~$ cat example.json
{
  "data": {
    "object": { 
      "user": {
        "id":1,
        "range": [-255,0,255],
        "notation":"big-O",
        "details": {
          "lat":0.000,"long":0.000,"time":42
        }
      },
      "groups":[
        {"id":2,"name": "foo"},
        {"id":3,"name": "bar"}
      ]
    },
    "metdata": {
      "list": [
        [ [1,42],[3.14, 98.6] ], 
        [ 3, 6, 9, "low" ],
        [{"x":1,"y":-1}]
      ],
      "ugly_nest": {"depth":{"test": true} }
    }
  },
  "log":"123abc"
}

Is there a jq one-liner I could use to transform into this output?

user@shell:~$ python flatten.py $(cat example.json)
data.object.user.id=1
data.object.user.range[0]=-255
data.object.user.range[1]=0
data.object.user.range[2]=255
data.object.user.notation=big-O
data.object.user.details.lat=0.0
data.object.user.details.long=0.0
data.object.user.details.time=42
data.object.groups[0].id=2
data.object.groups[0].name=foo
data.object.groups[1].id=3
data.object.groups[1].name=bar
data.metdata.list[0][0][0]=1
data.metdata.list[0][0][1]=42
data.metdata.list[0][0][1][0]=3.14
data.metdata.list[0][0][1][1]=98.6
data.metdata.list[1][0]=3
data.metdata.list[1][1]=6
data.metdata.list[1][2]=9
data.metdata.list[1][3]=low
data.metdata.list[2][].x=1
data.metdata.list[2][].y=-1
data.metdata.ugly_nest.depth.test=True
log=123abc

I wrote a python script to do this, but figured this could be done with jq and/or other bash built-ins.

Tried a ton of different things similar to the example below but can't seem to figure out how to join each nested instance properly:

cat example.json | jq '.. | to_entries? | [.key , .value] | join("=")'

Thanks for any help!

@bfontaine
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Did you check this StackOverflow question? It seems to match what you want.

@tmprender
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@bfontaine - thank you! This helps tremendously. This accomplishes the flattening aspect quite well, I can tweak to get formatting/output from here. Thank you very much!

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