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diff --git a/vendor/github.com/hashicorp/hcl/README.md b/vendor/github.com/hashicorp/hcl/README.md new file mode 100644 index 00000000..c8223326 --- /dev/null +++ b/vendor/github.com/hashicorp/hcl/README.md @@ -0,0 +1,125 @@ +# HCL + +[](https://godoc.org/github.com/hashicorp/hcl) [](https://travis-ci.org/hashicorp/hcl) + +HCL (HashiCorp Configuration Language) is a configuration language built +by HashiCorp. The goal of HCL is to build a structured configuration language +that is both human and machine friendly for use with command-line tools, but +specifically targeted towards DevOps tools, servers, etc. + +HCL is also fully JSON compatible. That is, JSON can be used as completely +valid input to a system expecting HCL. This helps makes systems +interoperable with other systems. + +HCL is heavily inspired by +[libucl](https://github.com/vstakhov/libucl), +nginx configuration, and others similar. + +## Why? + +A common question when viewing HCL is to ask the question: why not +JSON, YAML, etc.? + +Prior to HCL, the tools we built at [HashiCorp](http://www.hashicorp.com) +used a variety of configuration languages from full programming languages +such as Ruby to complete data structure languages such as JSON. What we +learned is that some people wanted human-friendly configuration languages +and some people wanted machine-friendly languages. + +JSON fits a nice balance in this, but is fairly verbose and most +importantly doesn't support comments. With YAML, we found that beginners +had a really hard time determining what the actual structure was, and +ended up guessing more often than not whether to use a hyphen, colon, etc. +in order to represent some configuration key. + +Full programming languages such as Ruby enable complex behavior +a configuration language shouldn't usually allow, and also forces +people to learn some set of Ruby. + +Because of this, we decided to create our own configuration language +that is JSON-compatible. Our configuration language (HCL) is designed +to be written and modified by humans. The API for HCL allows JSON +as an input so that it is also machine-friendly (machines can generate +JSON instead of trying to generate HCL). + +Our goal with HCL is not to alienate other configuration languages. +It is instead to provide HCL as a specialized language for our tools, +and JSON as the interoperability layer. + +## Syntax + +For a complete grammar, please see the parser itself. A high-level overview +of the syntax and grammar is listed here. + + * Single line comments start with `#` or `//` + + * Multi-line comments are wrapped in `/*` and `*/`. Nested block comments + are not allowed. A multi-line comment (also known as a block comment) + terminates at the first `*/` found. + + * Values are assigned with the syntax `key = value` (whitespace doesn't + matter). The value can be any primitive: a string, number, boolean, + object, or list. + + * Strings are double-quoted and can contain any UTF-8 characters. + Example: `"Hello, World"` + + * Multi-line strings start with `<<EOF` at the end of a line, and end + with `EOF` on its own line ([here documents](https://en.wikipedia.org/wiki/Here_document)). + Any text may be used in place of `EOF`. Example: +``` +<<FOO +hello +world +FOO +``` + + * Numbers are assumed to be base 10. If you prefix a number with 0x, + it is treated as a hexadecimal. If it is prefixed with 0, it is + treated as an octal. Numbers can be in scientific notation: "1e10". + + * Boolean values: `true`, `false` + + * Arrays can be made by wrapping it in `[]`. Example: + `["foo", "bar", 42]`. Arrays can contain primitives, + other arrays, and objects. As an alternative, lists + of objects can be created with repeated blocks, using + this structure: + + ```hcl + service { + key = "value" + } + + service { + key = "value" + } + ``` + +Objects and nested objects are created using the structure shown below: + +``` +variable "ami" { + description = "the AMI to use" +} +``` +This would be equivalent to the following json: +``` json +{ + "variable": { + "ami": { + "description": "the AMI to use" + } + } +} +``` + +## Thanks + +Thanks to: + + * [@vstakhov](https://github.com/vstakhov) - The original libucl parser + and syntax that HCL was based off of. + + * [@fatih](https://github.com/fatih) - The rewritten HCL parser + in pure Go (no goyacc) and support for a printer. |