Merge pull request #9829 from hashicorp/fix_9789
add variable gotcha to the variables docs not just the from-json hcl …
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@ -168,6 +168,72 @@ $ packer build -var='image_id_map={"us-east-1":"ami-abc123","us-east-2":"ami-def
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The `-var` option can be used any number of times in a single command.
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If you plan to assign variables via the command line, we strongly recommend that
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you at least set a default type instead of using empty blocks; this helps the
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HCL parser understand what is being set.
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For example:
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```hcl
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variable "pizza" {
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type = string
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}
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source "null" "example" {
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communicator = "none"
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}
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build {
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sources = [
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"source.null.example"
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]
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provisioner "shell-local" {
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inline = ["echo $PIZZA"]
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environment_vars = ["PIZZA=${var.pizza}"]
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}
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}
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```
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If you call the above template using the command
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```sh
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packer build -var pizza=pineapple shell_local_variables.pkr.hcl
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```
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then the Packer build will run successfully. However, if you define the variable
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using an empty block, the parser will not know what type the variable is, and it
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cannot infer the type from the command line, as shown in this example:
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```hcl
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variable "pizza" {}
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source "null" "example" {
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communicator = "none"
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}
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build {
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sources = [
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"source.null.example"
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]
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provisioner "shell-local" {
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inline = ["echo $PIZZA"]
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environment_vars = ["PIZZA=${var.pizza}"]
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}
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}
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```
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The above template will result in the error:
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```
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Error: Variables not allowed
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on <value for var.pizza from arguments> line 1:
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(source code not available)
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Variables may not be used here.
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```
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You can work around this either by quoting the variable on the command line, or
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by adding the type to the variable block as shown in the previous example.
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Setting the expected type is the more resilient option.
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```sh
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packer build -var 'pizza="pineapple"' shell_local_variables.pkr.hcl
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```
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### Variable Definitions (`.pkrvars.hcl`) Files
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To set lots of variables, it is more convenient to specify their values in a
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