In Autocad, what is the command that is used to rotate the grid at 45 degress?

UCS, then rotate around z axis

Enter snapang on the command line and after that put the angle value as45. its done!!

To rotate the snap grid

Enter snapang on the command line.

Enter a value for the new angle (45). (The default value is0.)

This action  will rotate the snap grid by45 degrees.

Note: The angle that you specify is relative to the current user coordinate system (UCS).

All through I never had a need of this command, I would do it the same way than Mr. ب عبدالله عبدالواحد العمر , if I would need to do this ... 

snapang then enter the value of rotation to45 degrees

write a command SNAPANG in command line