clear (or just c)
Issued without parameters, the clear command does pretty
heavy duty clearing of many of the GrADS internal settings.  Parameters
can be added to limit what is cleared when using more advanced
features.
WARNING: If you make any error in the syntax of clear
then GrADS does the full clear
clear norset        clears without resetting user options
clear events        flushes the events buffer (e.g., mouse clicks)
clear graphics      clears the graphics, but not the widgets
clear hbuff         clears
the  buffered display and turns off double buffer mode
clear button num    clears button  num 
clear rband num     clears rband  num 
clear dropmenu num  clears dropmenu num 
clear sdfwrite      clears sdfwrite file name and attributes without resetting other user options (2.0.a3+)
clear mask          clears contour label mask, which is enabled with the command 'set clab masked'(2.0.a7+)
clear shp           clears shapefile output file name and  attributes without resetting other user options (2.0.a9+)