Functions reference

Terraform policy includes built-in functions you can use when you write policies. You can also use many built-in Terraform functions, and write function plugins to implement reusable logic such as HTTP functions or arithmetic operations.

Terraform Policy functions

Terraform policy includes built-in functions to allow you to retrieve resources and data sources dynamically within your policies, make HTTP requests, and compare semantic version constraints:

• core::getresources - Return a list of resources that match the specified type and filter
• core::getdatasource - Return a data source that matches the specified type and filter
• core::gethttprequest - Make an HTTP GET request and return the results
• core::semverconstraint - Validate that a given version matches a version constraint

Plugin functions

In addition to the built-in functions, you can write plugins to implement your own Terraform policy functions. Refer to Policy plugins for more information.

Terraform library functions

Terraform policy also supports a number of standard Terraform library functions, which are in the 'core' namespace, referenced in policy configuration with core::<function-name>(arguments).

Numeric functions

• core::abs - Returns the absolute (positive) value of a given number
• core::ceil - Rounds a number up to the nearest whole number
• core::floor - Rounds a number down to the nearest whole number
• core::log - Returns the logarithm of a number to a given base
• core::max - Returns the largest of a set of numbers
• core::min - Returns the smallest of a set of numbers
• core::parseint - Parses a string as a whole number in the given base
• core::pow - Returns the result of a number raised to a given power
• core::signum - Returns a number indicating the sign of the input

String functions

• core::chomp - Removes any newline characters from the end of a string
• core::format - Produces a string by formatting other values according to a specification string
• core::endswith - Returns true if the string ends with the given characters
• core::indent - Adds a specified number of spaces to the beginning of each line
• core::join - Concatenates all elements of a list of strings into a single string
• core::lower - Converts all uppercase letters in a string to lowercase
• core::regex - Returns the first substring that matches the regular pattern
• core::regexall - Returns a list of all substrings that match the regular pattern
• core::split - Splits a string into a list of substrings
• core::startswith - Returns true if the string starts with the given characters
• core::strrev - Reverses the characters in a string
• core::substr - Returns a substring starting at offset with the specified length
• core::title - Converts the first letter of each word to uppercase
• core::trim - Removes leading or trailing characters specified in cutset
• core::trimprefix - Removes the specified prefix from the beginning
• core::trimspace - Removes all leading and trailing whitespace
• core::trimsuffix - Removes the specified suffix from the end
• core::upper - Converts all lowercase letters to uppercase

Collection functions

• core::alltrue - Returns true if all elements in a collection are true
• core::anytrue - Returns true if any element in a collection is true
• core::can - Evaluates an expression and returns true if it produces a result without errors
• core::chunklist - Splits a single list into fixed-size chunks
• core::coalescelist - Returns the first list that is not null or empty
• core::compact - Returns a new list with any null or empty string elements removed
• core::concat - Combines two or more lists into a single list
• core::contains - Determines whether a list contains at least one element equal to the given value
• core::distinct - Returns a new list containing only the unique elements
• core::element - Retrieves a single element from a list by its index
• core::flatten - Collapses a multi-dimensional list into a single-dimensional list
• core::formatlist - Produces a list of strings by formatting values
• core::keys - Returns a list of all the keys in a given map
• core::length - Returns the number of elements in a list, map, or string
• core::merge - Combines multiple maps into a single map
• core::range - Generates a list of numbers
• core::reverse - Reverses the order of elements in a list
• core::setintersection - Returns elements common to all given sets
• core::setproduct - Returns the Cartesian product of the given sets
• core::setsubtract - Returns elements from set1 not present in set2
• core::setunion - Returns all unique elements from all given sets
• core::slice - Returns a subset of elements from the original list
• core::sort - Sorts the elements of a list in ascending order
• core::values - Returns a list of all the values in a given map
• core::zipmap - Creates a map from two lists of equal length

Encoding/decoding functions

• core::csvdecode - Decodes CSV-formatted data into a list of maps
• core::jsondecode - Decodes a JSON-formatted string into a Terraform value
• core::jsonencode - Encodes a Terraform value into a JSON-formatted string
• core::yamldecode - Decodes a YAML-formatted string into a Terraform value
• core::yamlencode - Encodes a Terraform value into a YAML-formatted string

Terraform-specific functions

• core::timeadd - Adds a duration string to a timestamp
• core::timecmp - Compares two timestamps
• core::timestamp - Returns a string representation of the current date and time
• core::try - Evaluates expressions in order and returns the first one that does not produce an error