Enable matching of uppercase environment variables

[marpada]

Current Terraform Version

Terraform v0.12.7

Use-cases

The documentation about TF_VAR env variables says

On operating systems where environment variable names are case-sensitive, Terraform matches the variable name exactly as given in configuration, and so the required environment variable name will usually have a mix of upper and lower case letters as in the above example.

Our CD/CI managed system (Azure Pipelines) agent can run on Linux instances, but the agent converts environment variables to uppercase. https://github.com/microsoft/azure-pipelines-agent/issues/1645 To workaround this issue it would be good if Terraform could be configured to match uppercase environment variables.

Proposal

Introduce a command line flag allow matching of uppercase environment variables.

References

https://github.com/microsoft/azure-pipelines-agent/issues/1645