DB<130> $q=1
 
  DB<131> print $q + 4*5
21
  DB<132> print $q +4*5                           # what ???
 
  DB<133> use warnings; print $q +4*5
print() on unopened filehandle 1 at (eval 67)[/usr/share/perl/5.10/perl5db.pl:638] line 2.
 ...
  DB<134> use warnings; print $q+4*5
21 
  DB<135> use warnings; print $q+ 4*5
21