package Exception;
sub TIESCALAR { bless {}, $_[0] }
sub STORE { print "Setting the value of ", '$@', "\n" }
sub FETCH { 42 }

package main;
tie $@, 'Exception' or die "Unable to do what you want\n";
my ($foo, $bar) = (0, 0);
eval { $foo = 42 / $bar };
print "The value is : $@\n";
$@ = 'blah ';
print "Now the value is : $@\n";