Iterate over list of string using split or strings.Split

[air3ijai]

Hello,

We are trying to iterate over the list of strings to generate required AWS providers for Terraform.

The most appropriate way to do it probably by using strings.Split or split functions with a range. And it looks like strings.Split works only with a pipe-line, but in documentation we see both cases:

But we see different results for these cases

export REGIONS="eu-west-1 eu-west-2"

# strings.Split
gomplate -i '{{ strings.Split .Env.REGIONS " " }}'
[ ]

# strings.Split - pipeline
gomplate -i '{{ .Env.REGIONS | strings.Split " " }}'
[eu-west-1 eu-west-2]

# split
gomplate -i '{{ split .Env.REGIONS " " }}'
[eu-west-1 eu-west-2]

# split - pipeline
gomplate -i '{{ .Env.REGIONS | split " " }}'
[ ]

1. Is it correct that split can't be used with pipeline and strings.Split just with pipeline?
2. In provided example we got same result with or without parentheses - are they required or only for complex cases?

   gomplate -i '{{ range .Env.REGIONS | strings.Split " " }} {{ . }} {{ end }}'
   gomplate -i '{{ range (.Env.REGIONS | strings.Split " ") }} {{ . }} {{ end }}'

Example

Variable

export REGIONS="eu-west-1 eu-west-2"

Template

{{ range (split .Env.REGIONS " ") }}
provider "aws_split" {
  region = "{{.}}"
  alias  = "{{.}}"
}
{{ end }}

{{ range (.Env.REGIONS | split " ") }}
provider "aws_split_pipe" {
  region = "{{.}}"
  alias  = "{{.}}"
}
{{ end }}

{{ range (strings.Split .Env.REGIONS " ") }}
provider "aws_strings.Split" {
  region = "{{.}}"
  alias  = "{{.}}"
}
{{ end }}

{{ range (.Env.REGIONS | strings.Split " ") }}
provider "aws_strings.Split_pipe" {
  region = "{{.}}"
  alias  = "{{.}}"
}
{{ end }}

Result

provider "aws_split" {
  region = "eu-west-1"
  alias  = "eu-west-1"
}

provider "aws_split" {
  region = "eu-west-2"
  alias  = "eu-west-2"
}



provider "aws_split_pipe" {
  region = " "
  alias  = " "
}



provider "aws_strings.Split" {
  region = " "
  alias  = " "
}



provider "aws_strings.Split_pipe" {
  region = "eu-west-1"
  alias  = "eu-west-1"
}

provider "aws_strings.Split_pipe" {
  region = "eu-west-2"
  alias  = "eu-west-2"
}

[hairyhenderson]

Hi @air3ijai, thanks for taking the time to post this.

[...] And it looks like strings.Split works only with a pipe-line, [...]

No, it works both ways. The pipeline syntax is just syntactic sugar for providing the left-hand side of the | as the right-most argument.

I see in your example you've flipped the order of the two arguments, however:

# strings.Split
gomplate -i '{{ strings.Split .Env.REGIONS " " }}'
[ ]

What you actually want is {{ strings.Split " " .Env.REGIONS }}.

As for the difference between strings.Split and split, this is unfortunately by design. If you look at the documentation for each, you'll see split is not an alias for strings.Split, and split does redirect you to using strings.Split for a compatible version.

I don't know why split isn't deprecated - it should be, because in all cases strings.Split should be preferred as it works with pipelines.

I'm going to improve the documentation to make this difference more clear, and also deprecate the split function prior to later removal (and perhaps eventual re-introduction as an alias to strings.Split).

[hairyhenderson]

I've updated the documentation in #1538, and you can see a preview of the new documentation here: https://deploy-preview-1538--gomplate-docs.netlify.app/functions/strings/#strings-split

I'm going to merge it soon, but please let me know if you can think of anything else that would clarify - I can always change it again!

[air3ijai]

Hi @hairyhenderson, thank you for the clarification and documentation update!

Yes, looks like I missed the order and it works fine for now:

export REGIONS="eu-west-1 eu-west-2"

# strings.Split
gomplate -i '{{ strings.Split " " .Env.REGIONS }}'
[eu-west-1 eu-west-2]

# strings.Split - pipeline
gomplate -i '{{ .Env.REGIONS | strings.Split " " }}'
[eu-west-1 eu-west-2]

[hairyhenderson]

Awesome, glad to hear it's working for you!