yatee

README

What is yatee?

Yatee is a basic YAML templating engine whose input is a valid YAML file.

What does it support?

If, for, variable expansion, arithmetic expressions.

Show me some examples!

version: "3.4"
services:
  "@for i in 0..2":
    replica$i:
      image: superduperserver:latest
      command: /run $i
      port:
        - $(5000 + ($i*2))
        - $(5001 + ($i * 2))
  "@if ${myapp.debug}":
    debugger:
      image: debug
  "@if ! ${myapp.debug}":
    monitor:
      image: monitor
  "@for i in $myapp.services":
    "$i":
      image: $i:latest

When processed with the following settings file:

myapp:
  debug: false
  services:
    - nginx
    - redis

Will produce the following output:

services:
  monitor:
    image: monitor
  nginx:
    image: nginx:latest
  redis:
    image: redis:latest
  replica0:
    command: /run 0
    image: superduperserver:latest
    port:
    - "5000"
    - "5001"
  replica1:
    command: /run 1
    image: superduperserver:latest
    port:
    - "5002"
    - "5003"

How do I invoke it?

./yatee TEMPLATE_FILE SETTINGS_FILES...

How do I use it as a library?

The yatee go package exports the following two functions:

// LoadSettings loads a set of settings file and produce a property dictionary
func LoadSettings(files []string) (map[string]interface{}, error)
// Process resolves input templated yaml using values given in settings
func Process(inputString string, settings map[string]interface{}) (map[interface{}] interface{}, error)

Tell me more about the templating

All features at a glance

• $foo.bar and ${foo.bar} are replaced by the value of foo.bar in the settings structure. Nesting is allowed.
• ${foo?IF_TRUE:IF_FALSE} is replaced by IF_TRUE if foo in settings is true (not empty, 0 or false).
• $(expr) is evaluated as an arithmetic expression. Integers, parenthesis, and the operators '+-*/%' are supported. Note that there is no operator precedence, evaluation is from left to right.
• $$ is replaced by a single literal $ without any variable expansion.
• A YAML key of @for VAR in begin..end or @for VAR in VALUE LIST will inject the value in the parent node for each value of VAR.
• A YAML key of @if VALUE will inject its content in the parent node only if VAULE is not false (0, empty or 'false'). A prefix '!' is supported to negate the value. A @else dict can be specified under the @if node, and will be injected if the condition is false.
• A YAML key of @switch VALUE will inject it's sub-key's value matching VALUE to the parent node, or inject the value under the default key if present and no match is found.
• A YAML value of @if (EXPR) VALUE in a list will be replaced by VALUE if EXPR is true, suppressed otherwise

Variable expansion examples

All examples below use the following settings:

app:
  debug: true
  release: false
foo: bar
bar: baz
count: 2

Input	Output
${app.debug}	true
${foo}${bar}	barbaz
${$foo}	baz
$(1+2*3)	9
$(1+(2*3))	7
$($count + 40)	42
${app.debug?foo:bar}	foo
${app.release?foo:bar}	bar
$$foo	$$foo
$$$foo	$$bar

Control flow examples

Using the same settings as above.

If

"@if !$app.release":
 shown: nope
 "@else":
   shown: yes
somelist:
  - a
  - @if ($app.debug) b
  - @if ($app.release) c
  - d

produces:

shown: yes
somelist:
- a
- b
- d

For

"@for v in 0..$(count)":
  key$v: val$($v + 1)
"@for v in a b c":
  key$v: val$v

produces:

key0: val1
key1: val2
keya: vala
keyb: valb
keyc: valc

Switch

"@switch $foo":
  baz:
    isbaz: 1
  bar:
    isbar: 1
  default:
    isother: 1
"@switch $bar":
  foo:
    isfoo: 2
  default:
    isother:2

produces

isbar: 1
isother: 2

Documentation

Index

• Constants
• func LoadSettings(files []string) (map[string]interface{}, error)
• func Process(inputString string, settings map[string]interface{}, opts ...string) (map[interface{}]interface{}, error)
• func ProcessStrings(input, settings string) (string, error)

Constants

const (
	// OptionErrOnMissingKey if set will make rendering fail if a non-existing variable is used
	OptionErrOnMissingKey = "ErrOnMissingKey"
)

Functions

func LoadSettings

func LoadSettings(files []string) (map[string]interface{}, error)

LoadSettings loads a set of settings file and produce a property dictionary

func Process

func Process(inputString string, settings map[string]interface{}, opts ...string) (map[interface{}]interface{}, error)

Process resolves input templated yaml using values given in settings

func ProcessStrings

func ProcessStrings(input, settings string) (string, error)

ProcessStrings resolves input templated yaml using values in settings yaml