Built in Functions

Terraform provides many built in functions. These functions can be called by functionname() inside ${}. For example, ${file(config.txt)} will read the content of the file.

A list of commonly used functions,

Function	Description	Example
basename(path)	Returns filename of the a path	basename("/home/isuru/file.txt") returns file.txt
coalesce(string1, string2, ...)	Returns the first non empty value	coalsec("", "", "hello")
coalescelist(list1, list2, ...)	Returns the first non empty list	"
element(list, index)	Returns a single element from a list at the given index	element(module.vpc.public_subnet, count.index)
format(format, args, ...)	Formats a string/list according to the given format	format("server-%03d, count.index + 1) returns server-001, server-002
index(list, elem)	Finds the index of a given element in a list	index(aws_instance.foo.*.tags.Env, "prod")
join(delim, list)	Joins a list together with a delimiter	join(",", var.AMIS) returns "ami-123, ami-456, ami-789"
list(item1, item2, ...)	create a new list	join(":", list("a", "b", "c")) returns a:b:c
lookup(map, key, [default])	Perform a lookup on a map, using "key". Returns value representing "key" in the map(lookup("k", "v"), "k", "not found") returns "v"
lower(string)	returns lowercase value of "string"	lower("Hello") returns hello
map(key, value)	returns a new map using key:value	map("k", "v", "k2", "v2") returns: {"k" = "v", "k2" = "v2"}
merge(map1, map2, ...)	Merge maps(union)	merge(map("k", "v"), map("k2", "v2")) returns: {"k" = "v", "k2" = "v2"}
replace(string, search, replace)	Returns a search and replace on string	replace("aaab", "a", "b") returns bbbb
split(delim, string)	splits a string into a list	split(",", "a,b,c,d") returns ["a", "b", "c", "d"]
substr(string, offset, length)	Extract substring from string	substr("abcd", -3, 3)returns cde
timestamp()	returns RFC 3339 timestamp	"Server started at ${timestamp()}" Server started at 2021-05-27T10:42:46Z
uppser(string)	Returns uppsecased string	upper('string') returns STRING
uuid()	Returns a UUID string in RFC 4122 v4 format	uuid() returns: c5f44842-beaa-11eb-8529-0242ac130003
values(map)	returns values of a map	values(map("k", "v", "k2", "v2")) returns["v", "v2"]