Terraform: How to remove new line characters from a string

Terraform, an open-source infrastructure as code software tool developed by HashiCorp, enables users to define and provision data center infrastructure using a declarative configuration language. A common use case in Terraform scripting involves manipulating strings to fit specific formatting requirements, such as removing new line characters from a given string. This tutorial explores various methods to achieve this, offering insights from basic to advanced techniques.

Understanding New Line Characters

Before diving into Terraform-specific solutions, it’s crucial to understand what new line characters are. In most text-editing environments, pressing the ‘Enter’ or ‘Return’ key inserts a new line character, signifying the end of one line of text and the beginning of another. In Unix-like systems, it’s represented as \n, while in Windows environments, it appears as a combination of carriage return and new line characters, \r\n. Terraform’s cross-platform nature necessitates a flexible approach to handling these characters.

Basic String Replacement

The simplest method to remove new line characters from a string in Terraform is using the replace function. This function searches a given string for another string and replaces it with a third string. Below is a basic example:

variable "example_string" {
  default = "Hello\nWorld"
}

output "no_newlines" {
  value = replace(var.example_string, "\\n", "")
}

The output for the above code snippet would be HelloWorld, demonstrating how the replace function can effectively remove new line characters. Note the double backslash used to denote a single backslash in the search string, followed by the literal n character.

Advanced Use of String Functions

For more complex scenarios, Terraform offers a set of string functions that can be combined to manipulate strings in various ways. The trimspace function, which removes any whitespace characters (including new line characters) from the beginning and end of a string, can be useful in specific contexts:

output "trimmed" {
  value = trimspace(var.example_string)
}

This approach is slightly different, as it only removes new line characters at the extremes of the string, preserving any that exist within the body of the string.

Utilizing External Data Sources

In certain cases, Terraform configurations require manipulation of strings that aren’t known ahead of time but are fetched from external sources, such as files or APIs. The external data source allows Terraform to use information determined by an external program. Consider a scenario where a string is sourced from an external file containing new line characters:

data "external" "example" {
  program = ["bash", "-c", "echo -n $(cat input.txt) | tr -d '\n'"]
}

output "external_string" {
  value = data.external.example.result
}

This example leverages the Unix tr command to delete \n characters directly, before they are processed by Terraform. This method is highly effective for preprocessing complex data.

Regex-Based Solutions

For those familiar with regular expressions, Terraform’s regex function offers a powerful tool for string manipulation, including removing new line characters. Here’s a sample demonstration:

output "regex_example" {
  value = regex(".*", var.example_string)
}

This regex pattern, while simplistic, can be expanded upon to match specific conditions before performing a replace operation, making it a versatile option for advanced users.

Conclusion

Throughout this tutorial, we’ve explored several methods for removing new line characters from strings in Terraform, from straightforward replacements to leveraging external commands and utilizing regular expressions. By understanding these techniques, Terraform users can ensure their configurations are as clean and efficient as possible, keeping inline with best practices for infrastructure as code.