fix: moved os check to entry of func

common/shell-local/config.go

@@ -165,18 +165,17 @@ func Validate(config *Config) error {
 
 	// Check for properly formatted go os types
 	supported_syslist := []string{"darwin", "freebsd", "linux", "openbsd", "solaris", "windows"}
-	supported_os := false
 	if len(config.OnlyOn) > 0 {
 		for _, provided_os := range config.OnlyOn {
+			supported_os := false
 			for _, go_os := range supported_syslist {
 				if provided_os == go_os {
 					supported_os = true
 					break
 				}
-				if supported_os != true {
+			}
-					errs = packer.MultiErrorAppend(errs,
+			if supported_os != true {
-						fmt.Errorf("Invalid OS specified in only_on: '%s'", provided_os))
+				return fmt.Errorf("Invalid OS specified in only_on: '%s'", provided_os)
-				}
 			}
 		}
 	}

common/shell-local/run.go

@@ -28,6 +28,24 @@ type EnvVarsTemplate struct {
 }
 
 func Run(ui packer.Ui, config *Config) (bool, error) {
+	// Check if shell-local can even execute against this runtime OS
+	runCommand := false
+	if len(config.OnlyOn) > 0 {
+		for _, os := range config.OnlyOn {
+			if os == runtime.GOOS {
+				runCommand = true
+				break
+			}
+		}
+	} else {
+		runCommand = true
+	}
+	if !runCommand {
+		ui.Say(fmt.Sprintf("Skipping shell-local due to runtime OS"))
+		log.Printf("[INFO] (shell-local): skipping shell-local due to missing runtime OS")
+		return true, nil
+	}
+
 	scripts := make([]string, len(config.Scripts))
 	if len(config.Scripts) > 0 {
 		copy(scripts, config.Scripts)
@@ -59,50 +77,31 @@ func Run(ui packer.Ui, config *Config) (bool, error) {
 		if err != nil {
 			return false, err
 		}
+		ui.Say(fmt.Sprintf("Running local shell script: %s", script))
 
-		// Check if command can execute against runtime.
+		comm := &Communicator{
-		runCommand := false
+			ExecuteCommand: interpolatedCmds,
-		if len(config.OnlyOn) > 0 {
-			for _, os := range config.OnlyOn {
-				if os == runtime.GOOS {
-					runCommand = true
-				}
-			}
-		} else {
-			runCommand = true
 		}
 
-		if runCommand {
+		// The remoteCmd generated here isn't actually run, but it allows us to
-			ui.Say(fmt.Sprintf("Running local shell script: %s", script))
+		// use the same interafce for the shell-local communicator as we use for
-
+		// the other communicators; ultimately, this command is just used for
-			comm := &Communicator{
+		// buffers and for reading the final exit status.
-				ExecuteCommand: interpolatedCmds,
+		flattenedCmd := strings.Join(interpolatedCmds, " ")
-			}
+		cmd := &packer.RemoteCmd{Command: flattenedCmd}
-
+		log.Printf("[INFO] (shell-local): starting local command: %s", flattenedCmd)
-			// The remoteCmd generated here isn't actually run, but it allows us to
+		if err := cmd.StartWithUi(comm, ui); err != nil {
-			// use the same interafce for the shell-local communicator as we use for
+			return false, fmt.Errorf(
-			// the other communicators; ultimately, this command is just used for
+				"Error executing script: %s\n\n"+
-			// buffers and for reading the final exit status.
+					"Please see output above for more information.",
-			flattenedCmd := strings.Join(interpolatedCmds, " ")
+				script)
-
+		}
-			cmd := &packer.RemoteCmd{Command: flattenedCmd}
+		if cmd.ExitStatus != 0 {
-			log.Printf("[INFO] (shell-local): starting local command: %s", flattenedCmd)
+			return false, fmt.Errorf(
-			if err := cmd.StartWithUi(comm, ui); err != nil {
+				"Erroneous exit code %d while executing script: %s\n\n"+
-				return false, fmt.Errorf(
+					"Please see output above for more information.",
-					"Error executing script: %s\n\n"+
+				cmd.ExitStatus,
-						"Please see output above for more information.",
+				script)
-					script)
-			}
-			if cmd.ExitStatus != 0 {
-				return false, fmt.Errorf(
-					"Erroneous exit code %d while executing script: %s\n\n"+
-						"Please see output above for more information.",
-					cmd.ExitStatus,
-					script)
-			}
-		} else {
-			ui.Say(fmt.Sprintf("Skipping local shell script due to runtime OS: %s", script))
-			log.Printf("[INFO] (shell-local): skipping command due to runtime OS not specified.")
 		}
 	}