10. Built-In Functions

While Terraform is not an imperitive programming language such as Python, there are a number of functions you can use to manipulate variable values. These can be called when assigning values in a resource or data source, or when create locals. There are many more than we will discuss in this course, but here are a few common examples.

Mathematical Functions

• ceil - Rounds a decimal number up to the nearest whole number, e.g. ceil(4.1) returns 5
• floor - Rounds a decimal number down to the nearest whole number, e.g. floor(4.1) returns 4
• parseint - Converts a number represented as a string into a number, based on a given base, e.g. parseint("100", 10) returns 10, but parseint("100", 2) returns 4

String Functions

• replace - Replace all instances of a given substring within a string, e.g. replace("prp_123456", "prp_", "") returns "123456"
• lower - Converts a given string to all lower case, e.g. lower("BaNANas") returns "bananas"
• trimspace - Remove any whitespace (space, tabs, newlines etc.) from the start and end of a string, e.g. trimspace(" Hello, there \n\n") returns "Hello, there"

Collection Functions

• compact - Takes a list of strings and returns a new list with any null or empty string elements removed, e.g. compact(["a", "", "b", null, "c"]) returns ["a","b","c"]
• concat - Takes two or more lists and combines them into a single list, e.g. concat(["a", ""], ["b", "c"]) returns ["a","","b","c"]
• length - Determines the length of a given list, map, or string, e.g. length(["a", "b"]) returns 2

File Functions

• file - Load the contents of a local file, e.g. filecontent = file("${path.module}/data.txt")
• templatefile - Load the contents of a file and replace variable values from a given set, e.g. filecontent = templatefile("${path.module}/data.txt", my_vars)

Encoding Functions

• jsondecode - Convert a json string into a Terraform variable, e.g. data = jsondecode(local.file_content)
• base64decode - Convert base64-encoded data into a regular UTF-8 string, e.g. base64decode("SGVsbG8gV29ybGQ=") returns "Hello World"

Type-Conversion Functions

• tostring - Convert a numberl, or boolean into a string, e.g. tostring(1) returns "1" and tostring(true) returns "true"
• tobool - Convert the strings "true" or "false" into actual boolean values, e.g. tobool("true") returns true

These are a very small subset of all the functions you can use in Terraform, and you can find the full list here (opens in a new tab)

Exercise