Implement #IZ3

app/main.go

 	"fmt"
 	"io"
 	"os"
+	"strings"
 )
 
 type Context struct {
 	CommandTypeNone CommandType = iota
 	CommandTypeExternal
 	CommandTypeBuiltinExit
+	CommandTypeBuiltinEcho
 )
 
 func getCommand(ctx *Context) (Command, error) {
 	return command, nil
 }
 
-func parseTokens(str string) []string {
+func tokenize(str string) []string {
 	tokens := make([]string, 2)
-	tokens[0] = str[:len(str)-1]
+	tokens = strings.Fields(str)
 	return tokens
 }
 
 func parseCommand(command_line string) (Command, error) {
-	tokens := parseTokens(command_line)
+	tokens := tokenize(command_line)
 	if tokens[0] == "exit" {
 		return makeCommand(CommandTypeBuiltinExit, tokens), nil
 	}
+	if tokens[0] == "echo" {
+		return makeCommand(CommandTypeBuiltinEcho, tokens), nil
+	}
 	return makeCommandNone(), fmt.Errorf("%s: command not found", tokens[0])
 }
 
 		return
 	case CommandTypeBuiltinExit:
 		os.Exit(0)
+	case CommandTypeBuiltinEcho:
+		fmt.Fprintln(ctx.stdout, strings.Join(command.tokens[1:], " "))
 	}
 }