SAS: Drop variable if it exists

* =============================================================== ;
*         M A C R O   D R O P _ V A R _ I F _ E X I S T S
* =============================================================== ;

%macro drop_var_if_exists(SASFILE=,VAR=);

%* See also http://sasrunner.blogspot.com/2009/09/check-variable-exist-in-data-step-run.html;

data _null_;
dsid = open("&SASFILE");
call symput("var_exists", varnum(dsid, "&VAR"));
rc = close(dsid);
run;

%if (&var_exists eq 0) %then %do;
    %put Variable &VAR does not exist in &SASFILE ;
%end;
%else %do;
    proc sql noprint;
    alter table &SASFILE drop &VAR;
    quit;
    run;
    %put Variable &VAR was dropped from file &SASFILE ;
%end;

%mend drop_var_if_exists;




* =============================================================== ;
*    T E S T   M A C R O   D R O P _ V A R _ I F _ E X I S T S
* =============================================================== ;

* Create test dataset;
data work.mactest;
 set sashelp.class (obs=10);
run;

title "Before drops";
proc print data=work.mactest;
run;
title;

%drop_var_if_exists(SASFILE=work.mactest, VAR=name);
%drop_var_if_exists(SASFILE=work.mactest, VAR=xyz);
%drop_var_if_exists(SASFILE=work.mactest, VAR=age);

title "After drops";
proc print data=work.mactest;
run;
title;

* Done ;