Introduction

Lightweight template parser using typescript This parser was originally created to transform terraform files for different deployment environments, but it is well-suited to any build task which needs a lightweight template parser with minimal dependencies.

Installation

yarn add -D text-template-parser or npm i --save-dev text-template-parser

Syntax

The template syntax is similar to handlebars. There are 4 block types: assign, force-assign, if, and else. Blocks are declared using the following syntax:

### {{assign}}
### x = 4
### y = foo
### z = true
### {{/assign}}

All blocks must be terminated with a close tag ({{/tag}}), similar to HTML/XML.

# {{if}}

The {{if}} block evaluates a conditional javascript expression, with the scope being the config passed to the parser and the variables assigned in previous {{assign}} blocks, and writes the text within the block to the output if the conditional evaluates to true. Example:

    ### {{assign}}
    ### foo = bar
    ### {{/assign}}
    ### {{if foo === "bar"}}
    ### echo "foo === bar"
    ### {{/if}}
    ### {{else}}
    ### echo "foo !== bar"
    ### {{/else}}

The output of this transform will be

    echo "foo === bar"

# {{else}}

The {{else}} block inverts the conditional of the preceding {{if}} block and writes the text within the block only if the conditional of the preceding {{if}} block evaluates to false.

# {{assign}}

The {{assign}} block adds the variable assignments contained within to the current scope, without overwriting the scope passed to the parser. Numeric values are automatically parsed as numbers, "true" and "false" are parsed as booleans, and all other values are parsed as strings.

# {{force-assign}}

the {{force-assign}} block behaves the same as the {{assign}} block, except assignments within this block overwrite the config passed to the parser.

Usage

The parser can be consumed from typescript/javascript or from the cli.

# TS/JS usage

For ts/js usage:

import { TemplateParser } from "text-template-parser";

const testTemplate = `
    #!/bin/bash
    ### {{assign}}
    ### foo = bar
    ### {{/assign}}
    ### {{assign}}
    ### y = baz
    ### {{/assign}}
    ### {{if foo === "bar"}}
    ### echo "foo === bar"
    ### {{/if}}
    ### {{else}}
    ### echo "foo !== bar"
    ### {{/else}}
    echo "done"
    ### {{if x >= 0}}
    ### exit 0
    ### {{/if}}
    ### {{else}}
    ### exit 1
    ### {{/else}}
`;

const config = {
  x: 2,
  y: "foo",
};

const parser = new TemplateParser(testTemplate, config);
console.log(parser.parseTemplate());

This will log the following:

#!/bin/bash
echo "foo === bar"
echo "done"
exit 0

# cli usage

If the text contained in testTemplate from the previous example is in a file called testfile.txt, you can achieve the same result with yarn template-parser-cli testfile.txt -o testout.txt -v x=2 y=foo Additional documentation can be found by running yarn template-parser-cli -h