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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'
@jsmucr
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jsmucr commented Jun 6, 2022

@testillano Just add

| map(.name)

🙂

@testillano
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jq '.[] | select (.free == true) | map(.name)' test.json
jq: error (at test.json:18): Cannot index string with string "name"

Not sure if I understood, indeed it is not the name but the upper key what I need (node1, node4).

@jsmucr
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jsmucr commented Jun 6, 2022

@testillano Ah, I'm very sorry -- I was on my phone having a lunch apparently not paying enough attention. This should work:

to_entries | map(select(.value.free == true)) | map(.key)

https://jqplay.org/s/ouOA-ttrYuM

@fearphage
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fearphage commented Jun 6, 2022

You don't need the last call to map() since it's not an array.

jq '.[] | select(.free == true).name' test.json

Alternatively you could just use map() if you want an array:

jq 'map(select(.free == true).name)' test.json

@testillano
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I wanted the parents (node1, node4), so @jsmucr hint is enough:

jq 'to_entries | map(select(.value.free == true)) | map(.key)' test.json 
[
  "node1",
  "node4"
]

It is difficult to tune the jq philosophy ...
Thank you all !

@fearphage
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@testillano FYI you don't need to call map() twice:

jq 'to_entries | map(select(.value.free == true).key)'

@testillano
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testillano commented Jun 7, 2022

Thank you @fearphage , I will simplify it !

@ksemele
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ksemele commented Jun 10, 2022

Guys... how I can from json like that

[
  {
    "Key": "{ some_map_1 }",
    "Value": "{ another_map_1 }",
    "Timestamp": "date"
  },
  {
    "Key": "{ some_map_2 }",
    "Value": "{ another_map_2 }",
    "Timestamp": "date"
  },
]

Get raw data like that?

some_map_1, another_map_1
some_map_2, another_map_2

I tried something like that but I get wrong result((

$ cat test.txt | jq '.[] | .Key, ",",  .Value' -r
{ some_map_1 }
,
{ another_map_1 }
{ some_map_2 }
,
{ another_map_2 }

upd:
I used that finally:

cat test.txt |jq '.[] | {key : .Key, value: .Value}| .key+", "+.value' -r

But maybe yet another solution better?

@jsmucr
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jsmucr commented Jun 10, 2022

@ksemele How about this? :-)

map([.Key,.Value] | join(", ")) | .[]

@fearphage
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jq --raw-output '.[] | "\(.Key | gsub("^{ | }$"; "")), \(.Value | gsub("^{ | }$"; ""))"'

@mirisu2
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mirisu2 commented Jul 15, 2022

Hi,
I have an object and I would like to select from input_chunks all object where status.mem_size != "0b"
I tried like this .[] | select(.status.mem_size!="0b") or .input_chunks | select(.status.mem_size!="0b") but it didn't work :(
Maybe someone can help me?

{
  "storage_layer": {
    "chunks": {
      "total_chunks": 28,
      "mem_chunks": 27,
      "fs_chunks": 1,
      "fs_chunks_up": 0,
      "fs_chunks_down": 1
    }
  },
  "input_chunks": {
    "kube": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "28.6M"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    },
    "storage_backlog.1": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "0b"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    },
    "emitter_for_detect-nginx-ingress": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    },
    "emitter_for_detect-aaaa-logger": {
      "status": {
        "overlimit": false,
        "mem_size": "3.0M",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 23,
        "up": 23,
        "down": 0,
        "busy": 23,
        "busy_size": "3.0M"
      }
    },
    "emitter_for_detect-kong-proxy-logger": {
      "status": {
        "overlimit": false,
        "mem_size": "99.6K",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 4,
        "up": 4,
        "down": 0,
        "busy": 4,
        "busy_size": "99.6K"
      }
    },
    "emitter_for_detect-elastic-logs": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    },
    "emitter_for_detect-audit-logs": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    },
    "emitter_for_detect-other": {
      "status": {
        "overlimit": false,
        "mem_size": "0b",
        "mem_limit": "9.5M"
      },
      "chunks": {
        "total": 0,
        "up": 0,
        "down": 0,
        "busy": 0,
        "busy_size": "0b"
      }
    }
  }
}

@jsmucr
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jsmucr commented Jul 16, 2022

.input_chunks | to_entries | map(.value | select(.status.mem_size != "0b") | .chunks)

@mirisu2
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mirisu2 commented Jul 16, 2022

.input_chunks | to_entries | map(.value | select(.status.mem_size != "0b") | .chunks)

what if I would like to have keys emitter_for_detect... for everyone where mem_size != "0b" ?

@jsmucr
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jsmucr commented Jul 16, 2022

@mirisu2 I'm not sure if I understand the question but maybe this...? :)

.input_chunks | to_entries | map(select(.key | startswith("emitter_for_detect")) | select(.value.status | .mem_size != "0b")) | from_entries
{
  "emitter_for_detect-aaaa-logger": {
    "status": {
      "overlimit": false,
      "mem_size": "3.0M",
      "mem_limit": "9.5M"
    },
    "chunks": {
      "total": 23,
      "up": 23,
      "down": 0,
      "busy": 23,
      "busy_size": "3.0M"
    }
  },
  "emitter_for_detect-kong-proxy-logger": {
    "status": {
      "overlimit": false,
      "mem_size": "99.6K",
      "mem_limit": "9.5M"
    },
    "chunks": {
      "total": 4,
      "up": 4,
      "down": 0,
      "busy": 4,
      "busy_size": "99.6K"
    }
  }
}

@mirisu2
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mirisu2 commented Jul 16, 2022

Yes. You got it right!
But I got {}

@jsmucr
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jsmucr commented Jul 17, 2022

Maybe old jq version? Try https://jqplay.org/.

@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.

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