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  @ARGV ~~ /\.mdb$/i

if (grep { not /\.mdb$/i } @ARGV) {
  print STDERR "All parameters must be MDB files\n";
  exit;
}

@ARGV ~~ /\.mdb\z/
   or die "All parameters must be MDB files"

@ARGV ~~ sub {$_[0] !~ /\.mdb$/i}
   and die "All parameters must be MDB files"

@ARGV !~~ /\.mdb$/i
   and die "All parameters must be MDB files";

given($foo) {
  when (! /some regexp/) {...}
  ...
}

given($foo) {
  when ! (/some regexp/) {...}
  ...
}