Shell variables can be set from the shell with the set command. In addition, shell variables are set which correspond to definitions supplied on the .options line of the current circuit, and there are additional shell variables which are set automatically in accord with the current plot. The shell variables that are currently active can be listed with the set command given without arguments, and are also listed within the Variables window brought up from the Tools menu of the Tool Control window. In these listings, a `+' symbol is prepended to variables defined from a .options line in the current circuit, and a `*' symbol is prepended to those variables defined for the current plot. These variable definitions will change as the current circuit and current plot change. Some variables are read-only and may not be changed by the user, though this is not indicated in the listing.
Before a simulation starts, the options from the .options line of the current circuit are merged with any of the same name that have been set using the shell. The result of the merge is that options that are booleans will be set if set in either case, and those that take values will assume the value set through the shell if conflicting definitions are given. The merge will be suppressed if the shell variable noshellopts is set from the shell, in which case the only options used will be those from the .options line, and those that are redefined using the set command will be ignored.
There are many shell variables that have special meaning to WRspice. Note the difference between a variable and a vector -- a variable is manipulated with the commands set and unset, and may be substituted in a command line with the $varname notation. A vector is a datum which can be plotted, manipulated algebraically, and so forth.
While any variable may be set, only the following ones will have any significance to WRspice. In general, variables set in the .options line are available for expansion in $varname references, but do not otherwise affect the workings of the shell.