add "config get" command to print settings values

internal/cli/config/config.go

@@ -37,6 +37,7 @@ func NewCommand() *cobra.Command {
 	configCommand.AddCommand(initAddCommand())
 	configCommand.AddCommand(initDeleteCommand())
 	configCommand.AddCommand(initDumpCommand())
+	configCommand.AddCommand(initGetCommand())
 	configCommand.AddCommand(initInitCommand())
 	configCommand.AddCommand(initRemoveCommand())
 	configCommand.AddCommand(initSetCommand())

internal/cli/config/get.go

@@ -0,0 +1,88 @@
+// This file is part of arduino-cli.
+//
+// Copyright 2020 ARDUINO SA (http://www.arduino.cc/)
+//
+// This software is released under the GNU General Public License version 3,
+// which covers the main part of arduino-cli.
+// The terms of this license can be found at:
+// https://www.gnu.org/licenses/gpl-3.0.en.html
+//
+// You can be released from the requirements of the above licenses by purchasing
+// a commercial license. Buying such a license is mandatory if you want to
+// modify or otherwise use the software for commercial activities involving the
+// Arduino software without disclosing the source code of your own applications.
+// To purchase a commercial license, send an email to [email protected].
+
+package config
+
+import (
+	"os"
+	"reflect"
+
+	"github.com/arduino/arduino-cli/configuration"
+	"github.com/arduino/arduino-cli/internal/cli/feedback"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"gopkg.in/yaml.v2"
+)
+
+func initGetCommand() *cobra.Command {
+	getCommand := &cobra.Command{
+		Use:   "get",
+		Short: tr("Gets a setting value."),
+		Long:  tr("Gets a setting value."),
+		Example: "" +
+			"  " + os.Args[0] + " config get logging.level\n" +
+			"  " + os.Args[0] + " config get logging.file\n" +
+			"  " + os.Args[0] + " config get sketch.always_export_binaries\n" +
+			"  " + os.Args[0] + " config get board_manager.additional_urls",
+		Args: cobra.MinimumNArgs(1),
+		Run:  runGetCommand,
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			return configuration.Settings.AllKeys(), cobra.ShellCompDirectiveDefault
+		},
+	}
+	return getCommand
+}
+
+func runGetCommand(cmd *cobra.Command, args []string) {
+	logrus.Info("Executing `arduino-cli config get`")
+	key := args[0]
+	kind := validateKey(key)
+
+	if kind != reflect.Slice && len(args) > 1 {
+		feedback.Fatal(tr("Can't get multiple key values"), feedback.ErrGeneric)
+	}
+
+	var value interface{}
+	switch kind {
+	case reflect.Slice:
+		value = configuration.Settings.GetStringSlice(key)
+	case reflect.String:
+		value = configuration.Settings.GetString(key)
+	case reflect.Bool:
+		value = configuration.Settings.GetBool(key)
+	}
+
+	feedback.PrintResult(getResult{value})
+}
+
+// output from this command may require special formatting.
+// create a dedicated feedback.Result implementation to safely handle
+// any changes to the configuration.Settings struct.
+type getResult struct {
+	data interface{}
+}
+
+func (gr getResult) Data() interface{} {
+	return gr.data
+}
+
+func (gr getResult) String() string {
+	gs, err := yaml.Marshal(gr.data)
+	if err != nil {
+		// Should never happen
+		panic(tr("unable to marshal config to YAML: %v", err))
+	}
+	return string(gs)
+}