The docs for eval suggest this idiom:

     # alter $@ on nefarious repugnancy only
     {
        my $e;
        {
          local $@; # protect existing $@
          eval { test_repugnancy() };
          # $@ =~ /nefarious/ and die $@; # Perl 5.14 and higher only
          $@ =~ /nefarious/ and $e = $@;
        }
        die $e if defined $e
     }
[download]