Use reader and writer to make shell extensible

main.go

@@ -21,7 +21,7 @@ func main() {
 		showQueue()
 	}
 	if settings["interactive"] == "true" {
-		interactiveShell()
+		interactiveShell(os.Stdin, os.Stdout)
 	}
 }
 

shell.go

@@ -3,15 +3,17 @@ package main
 import (
 	"bufio"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 )
 
-func interactiveShell() {
-	fmt.Println("Let's try an interactive shell!")
-	scanner := bufio.NewScanner(os.Stdin)
+func interactiveShell(reader io.Reader, writer io.Writer) {
+	fmt.Fprintln(writer, "Let's try an interactive shell!")
+	scanner := bufio.NewScanner(reader)
 	for {
-		fmt.Print("> ")
+		var quitShell bool = false
+		fmt.Fprint(writer, "> ")
 		if !scanner.Scan() {
 			break
 		}
@@ -21,14 +23,26 @@ func interactiveShell() {
 			continue
 		}
 		cmd := textFields[0]
-		fmt.Printf("Read input: %q\n", textFields)
+		fmt.Fprintf(writer, "DEBUG - Read input: %q\n", textFields)
 
 		switch cmd {
-
+		case "help", "?":
+			printHelp(os.Stdout)
+		case "exit", "quit":
+			quitShell = true
 		default:
-			fmt.Printf("Unknown command '%s'\n", cmd)
+			fmt.Fprintf(writer, "Unknown command '%s'\n", cmd)
+			fmt.Fprintln(writer, "Use 'help' to display help command")
 		}
-
+		if quitShell == true {
+			break
 		}
-	fmt.Println("\nGoodbye!\n")
+	}
+	fmt.Fprintln(writer, "\nGoodbye!\n")
+}
+
+func printHelp(writer io.Writer) {
+	fmt.Fprintln(writer, "Available commands:")
+	fmt.Fprintln(writer, "?, help: display this output")
+	fmt.Fprintln(writer, "exit, quit: quit this program")
 }