Template Helpers / Functions

Helpers extend the template to generate or to transform content.

The helpers from handlebars_misc_helpers are included. This page is a copy of handlebars_misc_helpers/README.md at master · davidB/handlebars_misc_helpers, and it can be can be out-of-date.

Few helpers are included, but if you need more helpers, ask via an issue or a PR.

To use an helper:

// arguments are space separated
{{ helper_name arguments}}

To chain helpers, use parenthesis:

{{ to_upper_case (to_singular "Hello foo-bars") }}
// -> BAR

{{ first_non_empty (unquote (json_str_query "package.edition" (read_to_str "Cargo.toml") format="toml")) (env_var "MY_VERSION") "foo" }}
// -> 2018

see Handlebars templating language

• String transformation
• Http content
• Path extraction
• File
• Environment variable
• JSON & YAML & TOML
  • Helpers
  • Blocks
  • Edition via jsonnet
• Assign

String transformation

Http content

Helper able to render body response from an http request.

Path extraction

Helper able to extract (or transform) path (defined as string).

for the same input: "/hello/bar/foo.txt"

File

Helper to read file content.

Environment variable

Helper able to get environment variables.

Specials environment variables are predefined (some of them come from std::env::consts - Rust):

JSON & YAML & TOML

Helpers

• json_query query:String data:Json: Helper able to extract information from json using JMESPath syntax for query.
• json_str_query query:String data:String: Helper able to extract information from json using JMESPath syntax for query, data follows the requested format.
• json_to_str data:Json: convert a json data into a string following the requested format.
• str_to_json data:String: convert(parse) a string into a json following the requested format.

The optional requested format, is the format of the string with data:

• "json" (default if omitted)
• "json_pretty" json with indentation,…
• "yaml"
• "toml"
• "toml_pretty"

Blocks

{{#from_json format="toml"}}
{"foo": {"hello":"1.2.3", "bar":{"baz":true} } }
{{/from_json}}

[foo]
hello = "1.2.3"
[foo.bar]
baz = true

{{#to_json format="toml"}}
[foo]
bar = { baz = true }
hello = "1.2.3"
{{/to_json}}

{
  "foo": {
    "bar": {
      "baz": true
    },
    "hello": "1.2.3"
  }
}

{{#from_json format="toml"}}
{"foo":{"bar":{"baz":true}}}
{{/from_json}}

foo:
  bar:
    baz: true

{{#to_json format="yaml"}}
foo:
    bar:
        baz: true
{{/to_json}}

{
  "foo": {
    "bar": {
      "baz": true
    }
  }
}

Note: YAML & TOML content are used as input and output format for json data. So capabilities are limited to what json support (eg. no date-time type like in TOML).

Edition via jsonnet

For more advanced edition of json, you can use jsonnet.

A data templating language for app and tool developers

• See the doc of jsonnet for more samples, syntax info,…
• This block can be combined with conversion helper/block for YAML & TOML to provide edition capabilities for those format
• the output should a valid json, except if string_output = false is set as parameter of the block.

{{#jsonnet}}
local v = {"foo":{"bar":{"baz":false}}};
v {
  "foo" +: {
      "bar" +: {
          "baz2": true
      }
  }
}
{{/jsonnet}}

{
  "foo": {
      "bar": {
          "baz": false,
          "baz2": true
      }
  }
}

Assign

Helper able to assign (to set) a variable to use later in the template.