//reset will cause any existing file to be 
//overwritten with new contents
output file=loop1.out reset;
for i(1, 10, 1);
   print "loop 1 iteration " i;
endfor;
 
output file=loop2.out reset;
for i(1, 10, 1);
   print "loop 2 iteration " i;
endfor;

output off;

If the loops are nested, you can do this:

//Clear out files from previous run
output file=nestloop1.out reset;
output file=nestloop2.out reset;

for i(1, 10, 1);
  output file=nestloop1.out on;
  print "loop 1 iteration " i;
  for j(10, 100, 10);
      output file=nestloop2.out on;
      print "loop 2 iteration " j;
   endfor;
endfor;

output off;

If the output statement ends with ‘reset’, the next print statement will overwrite an existing file with the same name. If the output statement ends with
‘on’, the the print statements will be added to the end of any existing file.