Demo Functions and Conditional Expressions

Welcome to this hands-on tutorial where you’ll explore key OpenTofu functions and conditional expressions. We’ll run various examples in the OpenTofu console to see how they transform values and control resource creation in Terraform configurations.

Table of Contents

1. Floor Function
2. Title Function
3. Lookup Function
4. Common Functions Overview
5. Splitting a Colon-Separated String for IAM Users
6. Querying a Resource by Index
7. Finding the Index of a List Element
8. Uploading Files to S3 with for_each
9. Conditional Expressions in an EC2 Resource
10. Links and References

1. Floor Function

Use the floor function to round a number down to the nearest integer. What does floor(10.9) return?

Run in the console:

> tofu console
> floor(10.9)
10

2. Title Function

The title function capitalizes the first letter of each word in a string:

> tofu console
> title("user-generated password file")
"User-Generated Password File"

3. Lookup Function

Retrieve a value from a map by key, with a fallback default:

> tofu console
> lookup({ a = "apple", b = "banana" }, "a", "unknown")
"apple"

The first argument must be a map. If the key isn’t found, lookup returns the provided default.

4. Common Functions Overview

5. Splitting a Colon-Separated String for IAM Users

In your project directory:

cd ~/OpenTofu-projects/project-sonic

variables.tf contains:

variable "cloud_users" {
  type    = string
  default = "andrew:ken:faraz:mutsumi:peter:steve:braja"
}

Without modifying variables.tf, split cloud_users into a list and create an IAM user for each name. Add this to main.tf:

resource "aws_iam_user" "cloud" {
  count = length(split(":", var.cloud_users))
  name  = split(":", var.cloud_users)[count.index]
}

Initialize and apply:

tofu init
tofu plan
tofu apply

You should see seven IAM users created.

6. Querying a Resource by Index

To inspect a specific IAM user, launch the console:

> tofu console
> aws_iam_user.cloud[6].name
"braja"

7. Finding the Index of a List Element

Given this variable in variables.tf:

variable "sf" {
  type = list(string)
  default = [
    "ryu", "ken", "akuma", "seth", "zangief",
    "poison", "thawk", "rashid", "fang", "birdie",
  ]
}

Locate the index of "rashid":

> tofu console
> index(var.sf, "rashid")
7

8. Uploading Files to S3 with for_each

Your set of media paths is defined in var.media. An S3 bucket is declared in main.tf:

resource "aws_s3_bucket" "sonic_media" {
  bucket = var.bucket
}

Add this resource to upload each file:

resource "aws_s3_object" "upload_sonic_media" {
  for_each = var.media
  bucket   = aws_s3_bucket.sonic_media.id
  key      = substr(each.value, 7, length(each.value) - 7)
  source   = each.value
}

• for_each = var.media iterates over each path.
• key removes the leading /media/ (offset 7).
• source points to the original file.

Apply the changes:

tofu apply

All files will be uploaded to your S3 bucket.

9. Conditional Expressions in an EC2 Resource

Switch to the project-mario directory:

cd ~/opentofu-projects/project-mario

variables.tf includes:

variable "name" {
  type = string
}

variable "ami" {
  type    = string
  default = "ami-09331245601cf"
}

variable "small" {
  type    = string
  default = "t2.nano"
}

variable "large" {
  type    = string
  default = "t2.2xlarge"
}

Define an EC2 instance that chooses its size based on var.name:

resource "aws_instance" "mario_servers" {
  ami           = var.ami
  instance_type = var.name == "tiny" ? var.small : var.large

  tags = {
    Name = var.name
  }
}

Initialize and plan with -var:

tofu init
tofu plan -var='name="tiny"'
tofu plan -var='name="big"'
# instance_type = t2.2xlarge

This completes our walkthrough of OpenTofu functions and conditional expressions. Great job!

Links and References

• OpenTofu Documentation
• Terraform Language - Expressions
• AWS IAM User Resource
• AWS S3 Bucket & Object
• AWS EC2 Instance