What is the command you can use to set an environment variable named "var1"of type String?

Using `TF_VAR_VAR1` (uppercase `VAR1`) would set a Terraform variable named `VAR1`, not `var1`, as Terraform environment variable names are case-sensitive to the declared variable.

`set` is used in some shells but `export` is the standard for making environment variables available to child processes in a Unix-like environment; also, no value is specified.

`variable "var1" { type = "string"}` is Terraform HCL syntax for *declaring* a variable within a `.tf` file, not a shell command to *set* an environment variable.

To set a Terraform variable named `var1` using an environment variable in a Unix-like shell, the environment variable must be named `TF_VAR_var1`. The `export` command makes this variable available to child processes like Terraform.