if (grep {$_ eq $zero_arg} @ARRAY) and not grep {$_ eq $sec_arg} @anotherarray){
  doSomething();
}

##</code><code>##

for my $Str ($zero_arg, $sec_arg){
  die "$Str is not in routers.txt" unless grep {$_ eq $Str} @Routers;
  if (grep {$_ eq $Str} @Interfaces){
    # The string is a good name, and it appears in @Interfaces
    # so do something
  }
}

##</code><code>##

for my $Str ($zero_arg, $sec_arg){
  die "$Str is not in routers.txt" unless grep {$_ eq $Str} @Routers;
}
if (grep {$_ eq $zero_arg} @Interfaces and grep {$_ eq $sec_arg} @Interfaces){
  # They are both there
  # So do something
}