Terraform: Add substring between built-in interpolation functions

[radeksimko]

I can see this being useful in following situation:

resource "aws_subnet" "private" {
  count = "${var.number_of_azs}"

  vpc_id = "${aws_vpc.default.id}"
  cidr_block = "${element(split(",", lookup(var.subnet_cidrs, "private")), count.index)}"
  availability_zone = "${element(split(",", lookup(var.aws_avalability_zones, var.aws_region)), count.index)}"

  tags {
    Name = "${substr(-1, 1, element(split(",", lookup(var.aws_avalability_zones, var.aws_region)), count.index))}-private"
  }
}

so the important bit:

${substr(-1, 1, element(split(",", lookup(var.aws_avalability_zones, var.aws_region)), count.index))}

if the element returns e.g. eu-west-1a then turns into a, which means I can get

tags {
  Name = "a-private"
}

[blewa]

+1. My use case is explicit availability zone placement is several places using default values.

[iceycake]

+1

[conord33]

+1

[hoshy]

+1

[dtaylor-sfdc]

+1

[jasonmcintosh]

Solution I used if you need first character:
${format("%.1s", var.string)}
There's some other things you can do with the format of the string.
https://blog.golang.org/strings
and
https://golang.org/pkg/fmt/

[catsby]

Thank you for the suggestion @radeksimko – I'll bring this up internally and see if we can make it happen 😄

[StyleT]

Do we have any updates here?

[apparentlymart]

This isn't directly what this issue is about, but something similar to this is available as part of the aws_availability_zone data source. It exports separately the region and name_suffix attributes to allow (in @radeksimko's example) eu-west-1a to be split into eu-west-1 and a respectively, while simultaneously validating that the given AZ is valid by querying the AWS API.

[fillup]

I would like this feature as well to keep my code a bit cleaner. In the mean time here is how I'm doing substring to get just first 32 chars:

"${join("",slice(split("","reallylongstringherethatneedstobetrimmedtofirst32charsonly"),0,31))}"

[martin-flaregames]

Looks like this PR may explicitly solve this issue: https://github.com/hashicorp/terraform/pull/12870

[martin-flaregames]

@fillup your code saved my day, but I have to add that your example is not exactly doing what you state, it is generating a substring of the first 31 (and not 32) characters of the provided string, the second argument is end final index, exclusive. it should be:

"${join("",slice(split("","reallylongstringherethatneedstobetrimmedtofirst32charsonly"),0,32))}"

[nathanielks]

See https://github.com/hashicorp/terraform/issues/5157#issuecomment-347405959

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