If you want to check if a data set exists in a library, you don't need to open it. Use the EXIST function. This example will run the PROC MEANS only if SASHELP.CLASS is found.
%if %sysfunc(exist(sashelp.class)) %then %do;
proc means data=sashelp.class; run;
%end;
However, if you want to check for a condition where a particular variable exists, you do have to open the data set (or query the DICTIONARY tables like SASHELP.VCOLUMN -- plenty of papers/doc on that).
This example will include the variable height in the analysis only if it is found in the data set:
%macro VarExist(ds, var);
%local rc dsid result;
%let dsid = %sysfunc(open(&ds));
%if %sysfunc(varnum(&dsid, &var)) > 0 %then %do;
%let result = 1;
%put NOTE: Var &var exists in &ds;
%end;
%else %do;
%let result = 0;
%put NOTE: Var &var not exists in &ds;
%end;
%let rc = %sysfunc(close(&dsid));
&result
%mend VarExist;
proc means data=sashelp.class;
var age
%if %VarExist(sashelp.class, height) %then %do;
height
%end;
;
run;
Notice that both of these examples leverage the %if/%then[/%else] ability for using macro conditional expressions in open code, which has been a capability in the language for a long time now...but people forget that and tend to wrap everything in macro routines (force of habit and probably working off decades of old examples).
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