Which of the following is not a valid string function in Terraform?

split is a valid Terraform string function used to split a string into a list of substrings.

join is a valid Terraform string function used to concatenate elements of a list into a single string.

While Terraform does not have a direct `slice` string function, `substr` provides string slicing capabilities, making `chomp` the definitively invalid option among the choices.

chomp is not a valid built-in string function in Terraform; Terraform provides functions like `trimspace` for similar purposes. Terraform's official documentation lists various string functions such as `split`, `join`, `substr`, `replace`, etc., but `chomp` is not among them.