how to check if keyword parameter exist/is empty

[somebody]

say I have the following macro:

%macro test(var=);
data input; set input;
%if &var. ne %then %do; do something;%end;
%if &var. e %then %do; do something;%end;
run;
%mend;

but the check "%if &var. e" does not work.

How else should I do this?

[LinusH]

It's called eq, not e.

[Ksharp]

OR try 

%macro test(var=);
data input; set input;
%if %length(&var)  %then %do; do something;%end;
%if %length(&var)=0 %then %do; do something;%end;
run;
%mend;

[FreelanceReinh]

For a comprehensive overview and evaluation of the available methods see the SAS Global Forum 2009 paper "Is This Macro Parameter Blank?".