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, nginx configuration, and others similar.
The complete grammar can be found here, if you're more comfortable reading specifics, but a high-level overview of the syntax and grammar are listed here.
-
Single line comments start with
#or// -
Multi-line comments are wrapped in
/*and*/ -
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 continue any UTF-8 characters. Example:
"Hello, World" -
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.
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Boolean values:
true,false,on,off,yes,no. -
Arrays can be made by wrapping it in
[]. Example:["foo", "bar", 42]. Arrays can contain primitives and other arrays, but cannot contain objects. Objects must use the block syntax shown below.
Objects and nested objects are created using the structure shown below:
variable "ami" {
description = "the AMI to use"
}