Allow custom environment variable mapping in variable block

[zpatrick]

It would be nice to allow an optional override of the default TF_VAR_ environment variable mapping inside the variable block:

variable "endpoint" {
  default = "abc"
  env     = "ENDPOINT"
}

My use case: It becomes tedious keeping multiple environment variables in sync when working with terraform + another tool (or set of tools) that use environment variables for configuration. Today, I need to make sure ENDPOINT=abc is set for tool x, and TF_VAR_endpoint=abc is set for terraform. Allowing this override would remove this (albeit small) pain point.

I'd be happy to tackle this feature - but first wanted to get input from some of the core members in case this has deeper implications I'm not seeing.

[grubernaut]

Duplicate of #62, closing for now. I believe @mitchellh may have more to add, but it's definitely a topic that's talked about internally quite often. There are still a few core issues with adding environment variable interpolation at this stage. It's definitely something we wish to target in the future, as it's a heavily requested feature. Thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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