range Function

range generates a list of numbers using a start value, a limit value, and a step value.

range(max)
range(start, limit)
range(start, limit, step)

The start and step arguments can be omitted, in which case start defaults to zero and step defaults to either one or negative one depending on whether limit is greater than or less than start.

The resulting list is created by starting with the given start value and repeatedly adding step to it until the result is equal to or beyond limit.

The interpretation of limit depends on the direction of step: for a positive step, the sequence is complete when the next number is greater than or equal to limit. For a negative step, it's complete when less than or equal.

The sequence-building algorithm follows the following pseudocode:

let num = start
while num < limit: (or, for negative step, num > limit)
  append num to the sequence
  num = num + step
return the sequence

Because the sequence is created as a physical list in memory, Terraform imposes an artificial limit of 1024 numbers in the resulting sequence in order to avoid unbounded memory usage if, for example, a very large value were accidentally passed as the limit or a very small value as the step. If the algorithm above would append the 1025th number to the sequence, the function immediately exits with an error.

We recommend iterating over existing collections where possible, rather than creating ranges. However, creating small numerical sequences can sometimes be useful when combined with other collections in collection-manipulation functions or for expressions.

Examples

> range(3)
[
  0,
  1,
  2,
]

> range(1, 4)
[
  1,
  2,
  3,
]

> range(1, 8, 2)
[
  1,
  3,
  5,
  7,
]

> range(1, 4, 0.5)
[
  1,
  1.5,
  2,
  2.5,
  3,
  3.5,
]

> range(4, 1)
[
  4,
  3,
  2,
]

> range(10, 5, -2)
[
  10,
  8,
  6,
]

The range function is primarily useful when working with other collections to produce a certain number of instances of something. For example:

variable "name_counts" {
  type    = map(number)
  default = {
    "foo" = 2
    "bar" = 4
  }
}

locals {
  expanded_names = {
    for name, count in var.name_counts : name => [
      for i in range(count) : format("%s%02d", name, i)
    ]
  }
}

output "expanded_names" {
  value = local.expanded_names
}

# Produces the following expanded_names value when run with the default
# "name_counts":
#
# {
#   "bar" = [
#     "bar00",
#     "bar01",
#     "bar02",
#     "bar03",
#   ]
#   "foo" = [
#     "foo00",
#     "foo01",
#   ]
# }