add2optn.sas

%macro add2optn( op, addn, at=front );

  %* Modified version of Peter Crawfords addoptn found at
  %* http://www.sas.com/service/techtips/quicktips/
  %*
  %* 03/20/02 Richard A. DeVenezia
  %*          Do not change mainpart if addn is already in mainpart.
  %*          Note: If addn prefix matches another different addn already
  %*                present in op, then addn will *NOT* be added to rebuild.
  %*          This is not robust behaviour.  Invoke using shortest addn first
  %*          if you run into problems
  %* 03/16/09 Peter.Crawford
  %*          upcase parameter on comparison and use
  %*          %sysfunc( indexW()) instead on %index()
  %*          supports searching for the whole parameter not just substring
  %*;

  %local mainpart rebuild ;

  %let mainpart = %sysfunc( compress( %sysfunc( getoption( &op ) ), () )) ;
                         /* compress to remove the (parenthesis) */

  %if %sysfunc( indexw (%upcase(&mainpart), %upcase(&addn))) > 0 %then %do;
    %let rebuild = &mainpart ;
  %end;
  %else
  %if &at= front %then %do;
    %let rebuild = &addn &mainpart ;
  %end;
  %else %do;
    %let rebuild =       &mainpart &addn ;
  %end;

  &op = ( &rebuild )

%mend add2optn;