dasel

README

dasel

Dasel (short for data-selector) allows you to query and modify data structures using selector strings.

Comparable to jq / yq, but supports JSON, YAML, TOML and XML with zero runtime dependencies.

Table of contents

• Dasel
• Installation
• Notes
  • Preserved formatting and ordering
  • Memory Usage
• Usage
  • Select
  • Put
  • Put Object
• Supported file types
• Selectors
  • Property
  • Child
  • Index
  • Next available index
  • Dynamic
    • Using queries in dynamic selectors
• Examples
  • General
    • Filter JSON API results
  • jq to dasel
  • yq to dasel
  • Kubernetes
  • XML

Installation

You can import dasel as a package and use it in your applications, or you can use a pre-built binary to modify files from the command line.

Command line

Go

You can go get the main package and go should automatically build and install dasel for you.

go get github.com/tomwright/dasel/cmd/dasel

Binary on release

You can download a compiled executable from the latest release.

Linux amd64

This one liner should work for you - be sure to change the targeted release executable if needed. It currently targets dasel_linux_amd64.

curl -s https://api.github.com/repos/tomwright/dasel/releases/latest | grep browser_download_url | grep linux_amd64 | cut -d '"' -f 4 | wget -qi - && mv dasel_linux_amd64 dasel && chmod +x dasel
mv ./dasel /usr/local/bin/dasel

Mac OS amd64

You may have to brew install wget in order for this to work.

curl -s https://api.github.com/repos/tomwright/dasel/releases/latest | grep browser_download_url | grep macos_amd64 | cut -d '"' -f 4 | wget -qi - && mv dasel_macos_amd64 dasel && chmod +x dasel
mv ./dasel /usr/local/bin/dasel

Docker

You also have the option of using the docker image to run dasel for you.

echo '{"name": "Tom"}' | docker run -i --rm docker.pkg.github.com/tomwright/dasel/dasel:latest -p json '.name'
"Tom"

If you want to use a specific version of dasel simply change latest to the desired version.

Import

As with any other go package, just use go get.

go get github.com/tomwright/dasel

Notes

Preserved formatting and ordering

The formatting of files can be changed while being processed. Dasel itself doesn't make these changes, rather the act of marshaling the results.

In short, the output files may have properties in a different order but the actual contents will be as expected.

Memory usage

Dasel's method of querying data requires that the entire input document is stored in memory.

You should keep this in mind as the maximum filesize it can process will be limited by your system's available resources (specifically RAM).

Usage

dasel -h

An important note is that if no sub-command is given, dasel will default to select.

Select

dasel select -f <file> -p <parser> <selector>

Arguments

-f, --file

Specify the file to query. This is required unless you are piping in data.

If piping in data you can optionally pass -f stdin/-f -.

-p, --parser

Specify the parser to use when reading the file.

This is required if you are piping in data, otherwise dasel will use the given file extension to guess which parser to use.

See supported file types.

-s, --selector, <selector>

Specify the selector to use. See Selectors for more information.

If no selector flag is given, dasel assumes the first argument given is the selector.

This is required.

--plain

By default, dasel formats the output using the specified parser.

If this flag is used no formatting occurs and the results output as a string.

Example

Select the image within a kubernetes deployment manifest file:

dasel select -f deployment.yaml "spec.template.spec.containers.(name=auth).image"
"tomwright/auth:v1.0.0"

Piping data into the select:

cat deployment.yaml | dasel select -p yaml "spec.template.spec.containers.(name=auth).image"
"tomwright/auth:v1.0.0"

Put

dasel put <type> -f <file> -o <out> -p <parser> <selector> <value>

echo "name: Tom" | ./dasel put string -p yaml "name" Jim
name: Jim

Arguments

type

The type of value you want to put.

Available arguments:

• string
• int
• bool
• object - see Put Object

-f, --file

Specify the file to query. This is required unless you are piping in data.

If piping in data you can optionally pass -f stdin/-f -.

-o, --out

Specify the output file. If present, results will be written to the given file. If not present, results will be written to the input file (or stdout if none given).

To force output to be written to stdout, pass -o stdout/-o -.

-p, --parser

Specify the parser to use when reading/writing the input/output files.

This is required if you are piping in data, otherwise dasel will use the given file extension to guess which parser to use.

See supported file types.

-s, --selector, <selector>

Specify the selector to use. See Selectors for more information.

If no selector flag is given, dasel assumes the first argument given is the selector.

This is required.

value

The value to write.

Dasel will parse this value as a string, int, or bool from this value depending on the given type.

This is required.

Put Object

Putting objects works slightly differently to a standard put, but the same principles apply.

dasel put object -f <file> -o <out> -p <parser> -t <type> <selector> <values>

Arguments

-t, --type

The type of value you want to put.

You must repeat this argument for each value provided.

Available arguments:

• string
• int
• bool

-f, --file

Specify the file to query. This is required unless you are piping in data.

If piping in data you can optionally pass -f stdin/-f -.

-o, --out

Specify the output file. If present, results will be written to the given file. If not present, results will be written to the input file (or stdout if none given).

To force output to be written to stdout, pass -o stdout/-o -.

-p, --parser

Specify the parser to use when reading/writing the input/output files.

This is required if you are piping in data, otherwise dasel will use the given file extension to guess which parser to use.

See supported file types.

-s, --selector, <selector>

Specify the selector to use. See Selectors for more information.

If no selector flag is given, dasel assumes the first argument given is the selector.

This is required.

values

A space-separated list of key=value pairs.

Dasel will parse each value as a string, int, or bool depending on the related type.

This is required.

Example

echo "" | dasel put object -p yaml -t string -t int "my.favourites" colour=red number=3

Results in the following:

my:
  favourites:
    colour: red
    number: 3

Supported file types

Dasel attempts to find the correct parser for the given file type, but if that fails you can choose which parser to use with the -p or --parser flag.

JSON

-p json

Using golang.org/pkg/encoding/json.

TOML

-p toml

Using github.com/pelletier/go-toml.

YAML

-p yaml

Using gopkg.in/yaml.v2.

XML

-p xml

Using github.com/clbanning/mxj.

Arrays/Lists

Due to the way that XML is decoded, dasel can only detect something as a list if there are at least 2 items.

If you try to use list selectors (dynamic, index, append) when there are less than 2 items in the list you will get an error.

There are no plans to introduce a workaround for this but if there is enough demand it may be worked on in the future.

Selectors

Selectors define a path through a set of data.

Selectors are made up of different parts separated by a dot ., each part being used to identify the next node in the chain.

The following YAML data structure will be used as a reference in the following examples.

name: Tom
preferences:
  favouriteColour: red
colours:
- red
- green
- blue
colourCodes:
- name: red
  rgb: ff0000
- name: green
  rgb: 00ff00
- name: blue
  rgb: 0000ff

Property

Property selectors are used to reference a single property of an object.

Just use the property name as a string.

dasel select -f ./tests/assets/example.yaml -s "name"
Tom

• name == Tom

Child Elements

Just separate the child element from the parent element using a .:

dasel select -f ./tests/assets/example.yaml -s "preferences.favouriteColour"
red

• preferences.favouriteColour == red

Index

When you have a list, you can use square brackets to access a specific item in the list by its index.

dasel select -f ./tests/assets/example.yaml -s "colours.[1]"
green

• colours.[0] == red
• colours.[1] == green
• colours.[2] == blue

Next Available Index

The next available index selector is used when adding to a list of items. It allows you to append to a list.

• colours.[]

Dynamic

Dynamic selectors are used with lists when you don't know the index of the item, but instead want to find the index based on some other criteria.

Dasel currently supports key/query=value checks but I aim to support more check types in the future.

Look ups are defined in brackets. You can use multiple dynamic selectors within the same part to perform multiple checks.

dasel select -f ./tests/assets/example.yaml -s "colourCodes.(name=red).rgb"
ff0000

dasel select -f ./tests/assets/example.yaml -s "colourCodes.(name=blue)(rgb=0000ff)"
map[name:blue rgb:0000ff]

• colourCodes.(name=red).rgb == ff0000
• colourCodes.(name=green).rgb == 00ff00
• colourCodes.(name=blue).rgb == 0000ff
• colourCodes.(name=blue)(rgb=0000ff).rgb == 0000ff

If you want to refer to the value of a non-object value in a list, just define the key as value or ., meaning the current value. This may look something like (value=2).

Using queries in dynamic selectors

When performing a check dasel creates a new root node at the current position and then selects data using the given key as the query.

This allows you to perform complex queries such as...

echo `{
  "users": [
    {
      "name": {
        "first": "Tom",
        "last": "Wright"
      },
      "addresses": [
        {
          "primary": true,
          "number": 123
        },
        {
          "primary": false,
          "number": 456
        }
      ]
   }
  ]
}` | dasel -p json '.users.(.addresses.(.primary=true).number=123).name.first'
"Tom"

The above query in plain English may read as...

Give me the first name of the user who's primary address is at number 123

The resolution of that query looks something like this:

.users.(.addresses.(.primary=true).number=123).name.first
.users.(.addresses.[0].number=123).name.first
.users.[0].name.first

Examples

General

Filter JSON API results

The following line will return the download URL for the latest macOS dasel release:

curl https://api.github.com/repos/tomwright/dasel/releases/latest | dasel -p json --plain '.assets.(name=dasel_macos_amd64).browser_download_url'

jq to dasel

The follow examples show a set of jq commands and the equivalent in dasel.

Select a single value

echo '{"name": "Tom"}' | jq '.name'
"Tom"

echo '{"name": "Tom"}' | dasel -p json '.name'
"Tom"

Select a nested value

echo '{"user": {"name": "Tom", "age": 27}}' | jq '.user.age'
27

echo '{"user": {"name": "Tom", "age": 27}}' | dasel -p json '.user.age'
27

Select an array index

echo '[1, 2, 3]' | jq '.[1]'
2

echo '[1, 2, 3]' | dasel -p json '.[1]'
2

Append to an array of strings

echo '["a", "b", "c"]' | jq '. += ["d"]'
[
  "a",
  "b",
  "c",
  "d"
]

echo '["a", "b", "c"]' | dasel put string -p json -s '.[]' d
[
  "a",
  "b",
  "c",
  "d"
]

Update a string value

echo '["a", "b", "c"]' | jq '.[1] = "d"'
[
  "a",
  "d",
  "c"
]

echo '["a", "b", "c"]' | dasel put string -p json -s '.[1]' d
[
  "a",
  "d",
  "c"
]

Update an int value

echo '[1, 2, 3]' | jq '.[1] = 5'
[
  1,
  5,
  3
]

echo '[1, 2, 3]' | dasel put int -p json -s '.[1]' 5
[
  1,
  5,
  3
]

Overwrite an object

echo '{"user": {"name": "Tom", "age": 27}}' | jq '.user = {"name": "Frank", "age": 25}'
{
  "user": {
    "name": "Frank",
    "age": 25
  }
}

echo '{"user": {"name": "Tom", "age": 27}}' | dasel put object -p json -s '.user' -t string -t int name=Frank age=25
{
  "user": {
    "age": 25,
    "name": "Frank"
  }
}

Append to an array of objects

echo '{"users": [{"name": "Tom"}]}' | jq '.users += [{"name": "Frank"}]'
{
  "users": [
    {
      "name": "Tom"
    },
    {
      "name": "Frank"
    }
  ]
}

echo '{"users": [{"name": "Tom"}]}' | dasel put object -p json -s '.users[]' -t string name=Frank
{
  "users": [
    {
      "name": "Tom"
    },
    {
      "name": "Frank"
    }
  ]
}

yq to dasel

The follow examples show a set of yq commands and the equivalent in dasel.

Select a single value

echo 'name: Tom' | yq '.name'
"Tom"

echo 'name: Tom' | dasel -p yaml '.name'
Tom

Select a nested value

echo 'user:
  name: Tom
  age: 27' | yq '.user.age'
27

echo 'user:
       name: Tom
       age: 27' | dasel -p yaml '.user.age'
27

Select an array index

echo '- 1
- 2
- 3' | yq '.[1]'
2

echo '- 1
- 2
- 3' | dasel -p yaml '.[1]'
2

Append to an array of strings

echo '- a
- b
- c' | yq --yaml-output '. += ["d"]'
- a
- b
- c
- d

echo '- a
- b
- c' | dasel put string -p yaml -s '.[]' d
- a
- b
- c
- d

Update a string value

echo '- a
- b
- c' | yq --yaml-output '.[1] = "d"'
- a
- d
- c

echo '- a
- b
- c' | dasel put string -p yaml -s '.[1]' d
- a
- d
- c

Update an int value

echo '- 1
- 2
- 3' | yq --yaml-output '.[1] = 5'
- 1
- 5
- 3

echo '- 1
- 2
- 3' | dasel put int -p yaml -s '.[1]' 5
- 1
- 5
- 3

Overwrite an object

echo 'user:
  name: Tom
  age: 27' | yq --yaml-output '.user = {"name": "Frank", "age": 25}'
user:
  name: Frank
  age: 25


echo 'user:
  name: Tom
  age: 27' | dasel put object -p yaml -s '.user' -t string -t int name=Frank age=25
user:
  age: 25
  name: Frank

Append to an array of objects

echo 'users:
- name: Tom' | yq --yaml-output '.users += [{"name": "Frank"}]'
users:
  - name: Tom
  - name: Frank


echo 'users:
- name: Tom' | dasel put object -p yaml -s '.users[]' -t string name=Frank
users:
- name: Tom
- name: Frank

Kubernetes

The following should work on a kubernetes deployment manifest. While kubernetes isn't for everyone, it does give some good example use-cases.

Select the image for a container named auth

dasel select -f deployment.yaml -s "spec.template.spec.containers.(name=auth).image"
tomwright/x:v2.0.0

Change the image for a container named auth

dasel put string -f deployment.yaml -s "spec.template.spec.containers.(name=auth).image" "tomwright/x:v2.0.0"

Update replicas to 3

dasel put int -f deployment.yaml -s "spec.replicas" 3

Add a new env var

dasel put object -f deployment.yaml -s "spec.template.spec.containers.(name=auth).env.[]" -t string -t string name=MY_NEW_ENV_VAR value=MY_NEW_VALUE

Update an existing env var

dasel put string -f deployment.yaml -s "spec.template.spec.containers.(name=auth).env.(name=MY_NEW_ENV_VAR).value" NEW_VALUE

XML Examples

XML has some slight differences (such as attributes) that should be documented.

Query attributes

Decoded attributes are set as properties on the related object with a prefix of -.

echo '<data>
    <users primary="true">
        <name>Tom</name>
    </users>
    <users primary="false">
        <name>Frank</name>
    </users>
</data>' | dasel -p xml '.data.users[0].-primary'
true

Filtering on attributes

We can also filter on attributes since they are defined against the related object.

echo '<data>
    <users primary="true">
        <name>Tom</name>
    </users>
    <users primary="false">
        <name>Frank</name>
    </users>
</data>' | dasel -p xml '.data.users.(-primary=true).name'
Tom

Documentation

Index

• Variables
• func DynamicSelectorToGroups(selector string) ([]string, error)
• type Condition
• type EqualCondition
  • func (c EqualCondition) Check(other reflect.Value) (bool, error)
• type InvalidIndexErr
  • func (e InvalidIndexErr) Error() string
• type Node
  • func New(value interface{}) *Node
  • func (n *Node) InterfaceValue() interface{}
  • func (n *Node) Put(selector string, newValue interface{}) error
  • func (n *Node) Query(selector string) (*Node, error)
• type Selector
  • func ParseSelector(selector string) (Selector, error)
• type UnexpectedPreviousNilValue
  • func (e UnexpectedPreviousNilValue) Error() string
• type UnhandledCheckType
  • func (e UnhandledCheckType) Error() string
• type UnknownComparisonOperatorErr
  • func (e UnknownComparisonOperatorErr) Error() string
• type UnsupportedSelector
  • func (e UnsupportedSelector) Error() string
• type UnsupportedTypeForSelector
  • func (e UnsupportedTypeForSelector) Error() string
• type ValueNotFound
  • func (e ValueNotFound) Error() string

Variables

var ErrDynamicSelectorBracketMismatch = errors.New("dynamic selector bracket mismatch")

ErrDynamicSelectorBracketMismatch is returned when the number of opening brackets doesn't equal that of the closing brackets.

var ErrMissingPreviousNode = errors.New("missing previous node")

ErrMissingPreviousNode is returned when findValue doesn't have access to the previous node.

Functions

func DynamicSelectorToGroups

func DynamicSelectorToGroups(selector string) ([]string, error)

DynamicSelectorToGroups takes a dynamic selector and splits it into groups.

Types

type Condition

type Condition interface {
	Check(other reflect.Value) (bool, error)
}

Condition defines a Check we can use within dynamic selectors.

type EqualCondition

type EqualCondition struct {
	// Key is the key of the value to check against.
	Key string
	// Value is the value we are looking for.
	Value string
}

EqualCondition lets you check for an exact match.

func (EqualCondition) Check

func (c EqualCondition) Check(other reflect.Value) (bool, error)

Check checks to see if other contains the required key value pair.

type InvalidIndexErr

type InvalidIndexErr struct {
	Index string
}

InvalidIndexErr is returned when a selector targets an index that does not exist.

func (InvalidIndexErr) Error

func (e InvalidIndexErr) Error() string

Error returns the error message.

type Node

type Node struct {
	// Previous is the previous node in the chain.
	Previous *Node `json:"-"`
	// Next is the next node in the chain.
	Next *Node `json:"next,omitempty"`

	// Value is the value of the current node.
	Value reflect.Value `json:"value"`
	// Selector is the selector for the current node.
	Selector Selector `json:"selector"`
	// contains filtered or unexported fields
}

Node represents a single node in the chain of nodes for a selector.

func New

func New(value interface{}) *Node

New returns a new root node with the given value.

func (*Node) InterfaceValue

func (n *Node) InterfaceValue() interface{}

InterfaceValue returns the value stored within the node as an interface{}.

func (*Node) Put

func (n *Node) Put(selector string, newValue interface{}) error

Put finds the node using the given selector and updates it's value. It then attempts to propagate the value back up the chain to the root element.

func (*Node) Query

func (n *Node) Query(selector string) (*Node, error)

Query uses the given selector to query the current node and return the result.

type Selector

type Selector struct {
	// Raw is the full selector.
	Raw string `json:"raw"`
	// Current is the selector to be used with the current node.
	Current string `json:"current"`
	// Remaining is the remaining parts of the Raw selector.
	Remaining string `json:"remaining"`
	// Type is the type of the selector.
	Type string `json:"type"`
	// Property is the name of the property this selector targets, if applicable.
	Property string `json:"property,omitempty"`
	// Index is the index to use if applicable.
	Index int `json:"index,omitempty"`
	// Conditions contains a set of conditions to optionally match a target.
	Conditions []Condition `json:"conditions,omitempty"`
}

Selector represents the selector for a node.

func ParseSelector

func ParseSelector(selector string) (Selector, error)

ParseSelector parses the given selector string and returns a Selector.

type UnexpectedPreviousNilValue

type UnexpectedPreviousNilValue struct {
	Selector string
}

UnexpectedPreviousNilValue is returned when the previous node contains a nil value.

func (UnexpectedPreviousNilValue) Error

func (e UnexpectedPreviousNilValue) Error() string

Error returns the error message.

type UnhandledCheckType

type UnhandledCheckType struct {
	Value interface{}
}

UnhandledCheckType is returned when the a check doesn't know how to deal with the given type

func (UnhandledCheckType) Error

func (e UnhandledCheckType) Error() string

Error returns the error message.

type UnknownComparisonOperatorErr

type UnknownComparisonOperatorErr struct {
	Operator string
}

UnknownComparisonOperatorErr is returned when

func (UnknownComparisonOperatorErr) Error

func (e UnknownComparisonOperatorErr) Error() string

Error returns the error message.

type UnsupportedSelector

type UnsupportedSelector struct {
	Selector string
}

UnsupportedSelector is returned when a specific selector type is used in the wrong context.

func (UnsupportedSelector) Error

func (e UnsupportedSelector) Error() string

Error returns the error message.

type UnsupportedTypeForSelector

type UnsupportedTypeForSelector struct {
	Selector Selector
	Value    interface{}
}

UnsupportedTypeForSelector is returned when a selector attempts to handle a data type it can't handle.

func (UnsupportedTypeForSelector) Error

func (e UnsupportedTypeForSelector) Error() string

Error returns the error message.

type ValueNotFound

type ValueNotFound struct {
	Selector string
	Node     *Node
}

ValueNotFound is returned when a selector string cannot be fully resolved.

func (ValueNotFound) Error

func (e ValueNotFound) Error() string

Error returns the error message.