add docs and the option to list variables from inside the console

command/console.go

@@ -191,6 +191,8 @@ func (s *REPLSession) Handle(line string) (string, error) {
 		return "", ErrSessionExit
 	case strings.TrimSpace(line) == "help":
 		return s.handleHelp()
+	case strings.TrimSpace(line) == "variables":
+		return s.handleVariables()
 	default:
 		return s.handleEval(line)
 	}
@@ -205,6 +207,15 @@ func (s *REPLSession) handleEval(line string) (string, error) {
 	return rendered, nil
 }
 
+func (s *REPLSession) handleVariables() (string, error) {
+	varsstring := "\n"
+	for k, v := range s.Core.Context().UserVariables {
+		varsstring += fmt.Sprintf("%s: %+v,\n", k, v)
+	}
+
+	return varsstring, nil
+}
+
 func (s *REPLSession) handleHelp() (string, error) {
 	text := `
 The Packer console allows you to experiment with Packer interpolations.

website/source/docs/commands/console.html.md

@@ -0,0 +1,103 @@
+---
+description: |
+    The `packer fix` command allows you to experiment with Packer variable
+interpolations.
+layout: docs
+page_title: 'packer console - Commands'
+sidebar_current: 'docs-commands-console'
+---
+
+# `console` Command
+
+The `packer console` command allows you to experiment with Packer variable
+interpolations. You may access variables in the Packer config you called the
+console with, or provide variables when you call console using the -var or
+-var-file command line options.
+
+Type in the interpolation to test and hit <enter> to see the result.
+
+To exit the console, type "exit" and hit <enter>, or use Control-C.
+
+``` shell
+$ packer console my_template.json
+```
+
+The full list of options that the console command will accept is visible in the
+help output, which can be seen via `packer console -h`.
+
+## Options
+
+-   `-var` - Set a variable in your packer template. This option can be used
+    multiple times. This is useful for setting version numbers for your build.
+    example: `-var "myvar=asdf"`
+
+-   `-var-file` - Set template variables from a file.
+	example: `-var-file myvars.json`
+
+## REPL commands
+- `help` - displays help text for Packer console.
+
+- `exit` - exits the console
+
+- `variables` - prints a list of all variables read into the console from the
+  `-var` option, `-var-files` option, and template.
+
+## Usage Examples
+
+Let's say you launch a console using a Packer template `example_template.json`:
+
+
+```
+$ packer console example_template.json
+```
+
+You'll be dropped into a prompt that allows you to enter template functions and
+see how they're evaluated; for example, if the variable `myvar` is defined in
+your example_template's variable section:
+
+```
+"variables":{
+	"myvar": "asdfasdf"
+},
+...
+```
+and you enter `{{user `myvar`}}` in the Packer console, you'll see the value of
+myvar:
+
+```
+> {{user `myvar`}}
+> asdfasdf
+```
+
+From there you can test more complicated interpolations:
+
+```
+> {{user `myvar`}}-{{timestamp}}
+> asdfasdf-1559854396
+```
+
+And when you're done using the console, just type "exit" or CTRL-C
+
+```
+> exit
+$
+```
+
+If you'd like to provide a variable or variable files, you'd do this:
+
+```
+packer console -var "myvar=fdsafdsa" -var-file myvars.json example_template.json
+```
+
+If you don't have specific variables or var files you want to test, and just
+want to experiment with a particular template engine, you can do so by simply
+calling `packer console` without a template file.
+
+If you'd like to just see a specific single interpolation without launching
+the REPL, you can do so by echoing and piping the string into the console
+command:
+
+```
+$ echo {{timestamp}} | packer console
+1559855090
+```