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element(list, index) returns the element at position index in list. The index wraps around: if index is greater than the list length, it cycles back to the beginning.

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Signature

element(list list, index number) any

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Example

Assign each build to one of several artifact storage buckets in a round-robin fashion using the build number: 
variable "build_number" {
  description = "CI build number"
  type        = number
}

computed "bucket" {
  description = "Storage bucket for this build's artifacts"
  expression  = element(["artifacts-a", "artifacts-b", "artifacts-c"], var.build_number)
}

task "upload" {
  description = "Upload build artifacts to the assigned bucket"
  commands    = ["aws s3 cp dist/ s3://${computed.bucket}/build-${var.build_number}/ --recursive"]
}
Build 0 goes to artifacts-a, build 1 to artifacts-b, build 3 back to artifacts-a, and so on.

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Notes

  • index wraps using modulo arithmetic, so it never produces an out-of-bounds error.
  • To get the last element without knowing the length, use element(list, length(list) - 1).