} else if ("set".equals(command)) {
return new SetCommand();
} else if ("run".equals(command)) {
return new RunExe();
} else if ("ls".equals(command)) {
return new LsExe();
} else if ("dir".equals(command)) {
return new LsExe();
} else if ("cat".equals(command)) {
return new CatExe();
} else if ("mkdir".equals(command)) {
return new MkDirExe();
} else if ("ln".equals(command)) {