open(my $cities_fh => 'cities.txt') or die "ack: $!";
my %cities;
chomp, $cities{lc substr $_, 0, 3} = $_
  while <$cities_fh>;

open(my $devices_fh => 'devices.txt') or die "ack: $!";
/^dev-([a-z]+)/ and print "$cities{$1} $_"
  while <$devices_fh>;