Expressions and Functions

Interpolation, for expressions, built-in functions

HCL supports string templates ("${var.env}-db"), conditionals (var.env == "prod" ? 3 : 1), for expressions to transform lists and maps, and many built-in functions: string (upper, join, format), collection (merge, lookup, flatten), networking (cidrsubnet), encoding (jsonencode, yamlencode) and file functions. terraform console is an interactive place to try them.

Trying functions in terraform console, run

I ran this with Terraform 1.16.4 and the hashicorp/local 2.9.1 and hashicorp/random 3.9.1 providers, which manage local files and random values, so no cloud account was needed; each example starts from a fresh directory. Each expression is evaluated by terraform console: string helpers, cidrsubnet carving the third /24 out of a /16, merging maps, a lookup with a default, and a for expression.

for e in 'upper("shop")' 'join(",", ["web", "api"])' 'cidrsubnet("10.0.0.0/16", 8, 2)' 'merge({a = 1}, {b = 2})' 'lookup({dev = "t3.small", prod = "m7i.large"}, "prod", "t3.micro")' '[for s in ["web", "api"] : "${s}-svc"]'; do
  printf "%s\n  => " "$e"; echo "$e" | terraform console | tr -s "\n " " "; echo
done

Output:

upper("shop")
  => "SHOP" 
join(",", ["web", "api"])
  => "web,api" 
cidrsubnet("10.0.0.0/16", 8, 2)
  => "10.0.2.0/24" 
merge({a = 1}, {b = 2})
  => { "a" = 1 "b" = 2 } 
lookup({dev = "t3.small", prod = "m7i.large"}, "prod", "t3.micro")
  => "m7i.large" 
[for s in ["web", "api"] : "${s}-svc"]
  => [ "web-svc", "api-svc", ]

Prototype in the console

Test tricky expressions (cidrsubnet, for expressions over maps) in terraform console before putting them in code.

त्वरित जाँच: What does cidrsubnet("10.0.0.0/16", 8, 2) return?

• "10.0.2.0/24"
• "10.0.0.0/8"
• "10.2.0.0/16"
• "10.0.0.2/32"