Suppose that an interactive program gets responses from the statement INFILE CARDS. If you want to feed it under program control, you can push lines to the command stream that is read.

For example, suppose that a subroutine prompts a user to respond YES before performing some action. If you want to run the subroutine and feed the YES response without the user being bothered, you push the response as follows:

      /* the function that prompts the user */
   start delall;
      file log;
      put 'Do you really want to delete all records? (yes/no)';
      infile cards;
      input answer $;
      if upcase(answer)='YES' then
         do;
            delete all;
            purge;
            print "*** FROM DELALL:
            should see End of File (no records to list)";
            list all;
         end;
   finish;

The latter DO group is necessary so that the pushed YES is not read before the RUN statement. The following example illustrates the use of the preceding module DELALL:

      /* Create a dummy data set for delall to delete records  */
   xnum = {1 2 3, 4 5 6, 7 8 0};
   create dsnum1 from xnum;
   append from xnum;
      do;
         call push ('yes');
         run delall;
      end;