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HCL Conditionals

Hashicorp Language (HCL) supports the use of conditional statements for various things.

Conditions can be any expression that resolves to a boolean value.
We can use builtin functions and HCL conditional operators to perform conditional checks.

Ternary Operator

HCL supports the use of the ternary operator for conditional variable definitions and checks.

The basic syntax: 

condition ? true_val : false_val
This is functionally equivalent to the logic flow:
if condition then "true_val" else "false_val"

So we can use this to, say, give a default value to an empty variable.

var.a == "" ? "default-a" : var.a

This checks if var.a is an empty string (var.a == ""), and if that condition is true, we use the value "default-a". If the condition is false (the variable is not an empty string), then we use the value of the variable itself, var.a.

Operators

The logical operators for checking conditions supported by HCL include:

  • ==: Equal to
  • !=: Not equal to
  • >: Greater than
  • >=: Greater than or equal to
  • <: Less than
  • <=: Less than or equal to
  • !: NOT (Negate a condition)

HCL also supports the standard AND/OR operators found in most languages.

  • &&: AND
  • ||: OR

An example: 

condition = var.name != "" && lower(var.name) == var.name

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