accept "latest" as a valid -i parameter value

[drewmullen]

Thanks for maintaining this script! it works great!

When running this script in another packer build i ran into an issue. When allowing users to optionally set the packer version...

variable "packer_version" {
  type = string
  description = "semver of desired packer version, default is latest"
  default = ""

  validation {
    error_message = "Must be a valid semantic version or \"\" (default)."
    condition     = (
      var.packer_version == "" ||
      can(regex("^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)\\.(0|[1-9]\\d*)(?:-((?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\\.(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\\+([0-9a-zA-Z-]+(?:\\.[0-9a-zA-Z-]+)*))?$", var.packer_version))
    )
  }
}

...
  provisioner "shell" {
    execute_command = "chmod +x {{ .Path }}; {{ .Vars }} {{ .Path }} -i ${var.packer_version}"
    script           = "${path.cwd}/scripts/packer-install.sh"
  }

packer does not output a literal "" and the script errored:

./packer-install.sh -i   
Error - i requires an argument
usage: packer-install.sh [-i VERSION] [-a] [-c] [-h] [-v]
     -i VERSION : specify version to install in format '' (OPTIONAL)
     -a         : automatically use sudo to install to /usr/local/bin
     -c         : leave binary in working directory (for CI/DevOps use)
     -h         : help
     -v         : display packer-install.sh version

Allow setting "latest" OR "" gets around this