use strict;
use warnings;

my %router_of_interest = ( router1 => 1, router2 => 1 );

# ....

my %engine;
opendir DIA, '/';
while (my $file = readdir(DIA)) {
  next unless $file =~ /(.*)\.bbnplanet.net/;
  my $router = $1;

  next unless exists $router_of_interest{$router};

  my %HoH_engine;

  open(DIAFILE, "<$file") or die "Cannot open $file: $!\n";
  while (my $line = <DIAFILE>) {
    chomp $line;
    if ($line =~ /^\s*L3 Engine: (\d+)/i) {
      my $engine = $1;

      $HoH_engine{$router}{$engine} = 1;
    }
  }
  if (exists $HoH_engine{$router}){
    $engine{$router} = join(",", sort keys %{$HoH_engine{$router}});
  }
  else {
    $engine{$router} = "NA"; #GSR IOS version too old
  }
}

foreach my $key (sort keys %engine) {
  print "$key - Engine $engine{$key}\n";
}