terraform init                       # Initialize directory
terraform init -upgrade              # Upgrade providers
terraform init -reconfigure          # Reconfigure backend

terraform plan                       # Show execution plan
terraform plan -out=plan.tfplan      # Save plan
terraform plan -destroy              # Plan destroy
terraform plan -target=resource      # Target specific resource

terraform apply                      # Apply changes
terraform apply plan.tfplan          # Apply saved plan
terraform apply -auto-approve        # Skip confirmation
terraform apply -target=resource     # Apply specific resource

terraform destroy                    # Destroy infrastructure
terraform destroy -auto-approve      # Skip confirmation
terraform destroy -target=resource   # Destroy specific resource

terraform validate                   # Validate configuration
terraform fmt                        # Format code
terraform show                       # Show current state
terraform output                     # Show outputs
terraform refresh                    # Refresh state
terraform graph                      # Generate dependency graph

terraform state list                 # List resources
terraform state show resource        # Show resource
terraform state mv source dest       # Move resource
terraform state rm resource          # Remove from state
terraform state pull                 # Pull remote state
terraform state push                 # Push state

terraform workspace list             # List workspaces
terraform workspace new dev          # Create workspace
terraform workspace select dev       # Switch workspace
terraform workspace delete dev       # Delete workspace

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}
 
provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  
  tags = {
    Name = "WebServer"
  }
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t2.micro"
}
 
variable "availability_zones" {
  type    = list(string)
  default = ["us-east-1a", "us-east-1b"]
}

output "instance_ip" {
  value       = aws_instance.web.public_ip
  description = "Public IP of instance"
}

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"]
  
  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }
}

locals {
  common_tags = {
    Environment = "production"
    ManagedBy   = "Terraform"
  }
}

module "vpc" {
  source = "./modules/vpc"
  
  cidr_block = "10.0.0.0/16"
  name       = "main-vpc"
}

output "vpc_id" {
  value = module.vpc.vpc_id
}

terraform {
  backend "s3" {
    bucket = "my-terraform-state"
    key    = "prod/terraform.tfstate"
    region = "us-east-1"
  }
}

resource "aws_instance" "server" {
  count         = 3
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  
  tags = {
    Name = "Server-${count.index}"
  }
}

resource "aws_instance" "server" {
  for_each = toset(["web", "app", "db"])
  
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  
  tags = {
    Name = each.key
  }
}

resource "aws_instance" "server" {
  count = var.create_instance ? 1 : 0
  
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

resource "aws_security_group" "example" {
  name = "example"
  
  dynamic "ingress" {
    for_each = var.ingress_rules
    content {
      from_port   = ingress.value.from_port
      to_port     = ingress.value.to_port
      protocol    = ingress.value.protocol
      cidr_blocks = ingress.value.cidr_blocks
    }
  }
}

# String functions
upper("hello")
lower("HELLO")
title("hello world")
format("Hello, %s", var.name)
 
# Numeric functions
min(1, 2, 3)
max(1, 2, 3)
ceil(5.1)
floor(5.9)
 
# Collection functions
length(var.list)
concat(list1, list2)
merge(map1, map2)
lookup(map, "key", "default")
 
# Type conversion
tostring(123)
tonumber("123")
tolist(set)
toset(list)

terraform import aws_instance.web i-1234567890abcdef0