IDL help

help : lists all active variables, their characteristics, compiled programs, information on storage areas, etc.; various options. But does not explain commands. There are many optional keywords for use with help. Examples are given below. To get a full list, type ?help.

help,/rou : prints argument list for all compiled routines (other than intrinsic IDL routines). Lists procedures and functions separately.
help,/sy : prints current values of all "system variables", which are special variables known to all routines. Names of these begin with a "!", e.g. !dir, !path, etc.
help,/rec : prints contents of command recall buffer in reverse order
help,/dev : prints parameter settings for current graphics device
help,/mem : lists current memory usage