resource "null_resource" "example" {
  count = 3

  provisioner "local-exec" {
    command = "echo ${count.index}"
  }
}

null_resource.example[0] (local-exec): 0
null_resource.example[1] (local-exec): 1
null_resource.example[2] (local-exec): 2

variable "bucket_names" {
  description = "Names for the S3 buckets"
  type        = list(string)
  default     = ["111-first-bucket", "222-second-bucket", "333-third-bucket"]
}

resource "aws_s3_bucket" "example" {
  count  = length(var.bucket_names)
  bucket = var.bucket_names[count.index]
}

$ terraform state list
aws_s3_bucket.example[0]
aws_s3_bucket.example[1]
aws_s3_bucket.example[2]

resource "null_resource" "example" {
  for_each = {
    a = "one"
    b = "two"
  }

  provisioner "local-exec" {
    command = "echo ${each.key} - ${each.value}"
  }
}

null_resource.example["b"] (local-exec): b - two
null_resource.example["a"] (local-exec): a - one

provider "aws" {
  region = "ap-northeast-1"
}

variable "security_groups" {
  description = "A map of security group names and their inbound port numbers"
  type        = map(number)
  default = {
    web-sg     = 80
    ssh-sg     = 22
    database-sg = 3306
  }
}

resource "aws_security_group" "my_security_groups" {
  for_each = var.security_groups

  name        = each.key
  description = "Security group for ${each.key}"
  vpc_id      = "vpc-xxxxxxxxxxxxxxx"

  ingress {
    from_port   = each.value
    to_port     = each.value
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = each.key
  }
}

locals {
  numbers = [1, 2, 3, 4]
  doubled = [for n in local.numbers : n * 2]
}

output "doubled_numbers" {
  value = local.doubled
  description = "Numbers multiplied by 2"
}

Outputs:

doubled_numbers = [
  2,
  4,
  6,
  8,
]

locals {
  fruit_colors = {
    apple  = "green"
    banana = "yellow"
    cherry = "red"
  }
  capitalized_colors = {for f, c in local.fruit_colors : f => upper(c)}
}

output "fruit_colors" {
  value = local.fruit_colors
  description = "fruit"
}

Outputs:

fruit_colors = {
  "apple" = "green"
  "banana" = "yellow"
  "cherry" = "red"
}

locals {
  numbers = [1, 2, 3, 4, 5]
  evens = [for n in local.numbers : n if n % 2 == 0]
}

output "fruit_colors" {
  value = local.evens
  description = "evens"
}

Outputs:

evens_numbers = [
  2,
  4,
]