for - transform a list or map
variable "names" {
default = ["alice", "bob", "carol"]
}
locals {
upper_names = [for n in var.names : upper(n)]
name_lengths = { for n in var.names : n => length(n) }
}
# upper_names = ["ALICE", "BOB", "CAROL"]
# name_lengths = { alice = 5, bob = 3, carol = 5 }
if - conditional value
variable "env" {
default = "prod"
}
locals {
instance_type = var.env == "prod" ? "t3.large" : "t3.micro"
}
for + if - transform and filter together
variable "users" {
default = [
{ name = "alice", active = true },
{ name = "bob", active = false },
{ name = "carol", active = true },
]
}
locals {
active_upper = [for u in var.users : upper(u.name) if u.active]
}
# active_upper = ["ALICE", "CAROL"]
iterating over a map
variable "buckets" {
default = {
logs = "us-east-1"
backups = "eu-west-1"
}
}
locals {
bucket_arns = { for name, region in var.buckets : name => "arn:aws:s3:::${name}-${region}" }
}
flattening with flatten()
When you have nested lists - e.g. multiple groups each with multiple ports - use flatten() with for:
locals {
services = {
api = ["8080", "8443"]
metrics = ["9090"]
}
all_ports = flatten([
for svc, ports in local.services : [
for port in ports : "${svc}:${port}"
]
])
# all_ports = ["api:8080", "api:8443", "metrics:9090"]
}
Originally published at https://bard.sh/posts/hcl_expressions/
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