Terraform String Functions - Complete Reference with Examples

# format — sprintf-style string formatting
output "name" {
  value = format("web-%s-%02d", var.environment, 1)
  # "web-prod-01"
}

# formatlist — format each item in a list
output "names" {
  value = formatlist("web-%s-%02d", var.environment, [1, 2, 3])
  # ["web-prod-01", "web-prod-02", "web-prod-03"]
}

# join — combine list into string
output "csv" {
  value = join(",", ["a", "b", "c"])
  # "a,b,c"
}

# split — break string into list
output "parts" {
  value = split(",", "a,b,c")
  # ["a", "b", "c"]
}

# Common pattern: create comma-separated security group IDs
output "sg_ids" {
  value = join(",", aws_security_group.main[*].id)
}

# Simple replacement
output "clean_name" {
  value = replace("my_resource_name", "_", "-")
  # "my-resource-name"
}

# Regex replacement (wrap pattern in forward slashes)
output "no_digits" {
  value = replace("web-server-01", "/[0-9]+/", "XX")
  # "web-server-XX"
}

output "lower" { value = lower("Hello World") }     # "hello world"
output "upper" { value = upper("Hello World") }     # "HELLO WORLD"
output "title" { value = title("hello world") }     # "Hello World"

output "trimmed"  { value = trimspace("  hello  ") }        # "hello"
output "no_prefix" { value = trimprefix("arn:aws:s3:::bucket", "arn:aws:s3:::") }  # "bucket"
output "no_suffix" { value = trimsuffix("server.example.com.", ".") }  # "server.example.com"
output "trim_chars" { value = trim("?!hello?!", "?!") }     # "hello"

# substr(string, offset, length)
output "first_8" {
  value = substr("us-east-1a", 0, 9)
  # "us-east-1"
}

# Extract first match
output "version" {
  value = regex("v([0-9]+\\.[0-9]+)", "terraform-v1.5.7")
  # ["1.5"]
}

# Extract all matches
output "numbers" {
  value = regexall("[0-9]+", "web-01-app-02")
  # ["01", "02"]
}

# Validate format
output "is_valid_cidr" {
  value = can(regex("^[0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+/[0-9]+$", var.cidr))
}

output "is_prod" {
  value = startswith(var.environment, "prod")  # true/false
}

output "has_suffix" {
  value = endswith(var.hostname, ".internal")
}

# strcontains (Terraform 1.5+)
output "is_aws" {
  value = strcontains(var.provider_arn, "aws")
}

# Remove trailing newline
output "clean" { value = chomp("hello\n") }  # "hello"

# Indent multi-line string
output "indented" {
  value = indent(4, "line1\nline2\nline3")
  # "line1\n    line2\n    line3"
}

locals {
  name_prefix = lower(format("%s-%s", var.project, var.environment))
}

resource "aws_s3_bucket" "data" {
  bucket = "${local.name_prefix}-data"
  # "myapp-prod-data"
}

locals {
  arn_parts  = split(":", var.role_arn)
  account_id = local.arn_parts[4]
  role_name  = trimprefix(local.arn_parts[5], "role/")
}

locals {
  clean_name = lower(trimspace(replace(var.user_input, "/[^a-zA-Z0-9-]/", "")))
}