#!/usr/bin/perl

use warnings;
use strict;

my $awsGone = "/ansible/awsGone";
my $awsLists = "/ansible/awsLists";

#open file for appending
open(APPEND,'>>',"$awsGone") || die("canot open $awsGone,$!"); 

#open AWSlIST file for reading
open(READ, '<', $awsLists) || die("Could not open file, $!");

#open AWSGONE file for reading
open(READGONE, '<', $awsGone) || die("Could not open file, $!");
my @gone = <READGONE>;

my @ips;
@ips = <READ>;
foreach my $addy(@ips)
{
chomp($addy);
#Test if up

my $retreval=system qq{nc -w 1 $addy 22 > /dev/null 2>&1};

##if filesd are good, leave them alone, but if bad put them in $awsGon
+e
if($retreval==0)
      {
    print "This up -> $addy\n";
        }
    else
         {
                #check if file is empty, because after ansible runs it
+ clears this file
        if(-z "$awsGone")
        {
                print "Host not up\n";
        print APPEND "$addy\n";

            #remove the dead ip from awsLists
               system qq{sed -i "/$addy/d" "$awsLists"};
        }
        else
           {
                         ##file is not empty so check if ip is already
+ in the file 
             my @match = grep{/$addy/}@gone ;
              if (@match)
               {
                print "already exists\n";
                      system qq{sed -i "/$addy/d" "$awsLists"};
                  }
                else
                {
                            print "Host not up \n";
                 print APPEND "$addy\n";
                system qq{sed -i "/$addy/d" "$awsLists"};
                }

                 }
    
           }

    }



close APPEND;
close READ;
close READGONE;
[download]

my %down;

open my $ifh, '<', $hostfile or die "Can't read '$hostfile: $!\n";

while(my $addy = <$ifh>) {
    chomp $addy;
    $down{$addy} = system qq{nc -w 1 $addy 22 > /dev/null 2>&1}; # 0 =
+ up, not 0 = down
}
[download]

@down=<$ifh>;
foreach my $line(@down)
{
push @down{$addy}, $_ ;
}
or
@down{$addy}=<$ifh>;
[download]

    $down{$addy} = 1 unless ! $down{$addy};
    delete $down{$addy} if exists $down{$addy} and ! $down{$addy};
}
[download]

print $ifh sort keys %down;
[download]

For the above could I have said the following to put the dead ips into the hash ? Is there a difference?

Yes. There may be hosts in your down file which at that time were down, but at the current run are up again.

Also I am not understanding your logic on this line, all ips dead and alive are now in keys %down, you are assigning the value of 1 unless the ip is not apart of keys %down?

I am assigning the value 1 to the key in %down unless the host is not down, which implies it even exists in the hash %down and its value is not 0. So, hosts which aren't present anymore in the hosts file, but in the down file, are skipped. Then in the next line I delete the host if present in %down if it happens to be up.

then lastly, couldn't I just have said below, or you had to go through the hash to get \n formatting?

The below is wrong because it uses $ifh, which is input filehandle here, and because only a bare print implies $_, while print to an explicit filehandle does not. You have to mention $_. To get a newline at the end of each print operation, you have to mention that as well, unless you set $\ (output record separator, see perlvar)

@list = (a..z);
{ # ok for STDOUT
  local $\ = $/; # set output record sep to input record sep for this 
+block
  print for @list;
}

{ # wrong
  open my $fh,'>', 'foo' or die "Oops: foo - $!\n";
  local $\ = $/;
  print $fh for @list; # WRONG. This prints GLOB(0x1945bd8) or such 26
+ times
}
# file 'foo' closed here, since $fh is out of scope

{ # ok
  open my $fh,'>', 'bar' or die "Oops: bar - $!\n";
  my $fh = select $fh; # $fh now default filehandle
  local $\ = $/;
  print for @list; # OK
  select $fh; # restore STDOUT as default filehandle
}
# file 'bar' closed here, since $fh is out of scope
[download]

Running the above, you will have a..z printed to STDOUT, each character on a line, a file "foo" with 0 bytes and a file "bar" with 52 bytes.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

Thank you for the explanation, but in this example I learnt it is possible to print hash keys directly to an array without doing a for loop. I think the difference is in your example its an array you want to print to a filehandle

if( keys %old > $oldsize ) # only write if new ips added
  {
  open my $out, '>', $awsLists or die "$! opening $awsLists";
##print directly to the file the new keys difference
  print $out sort keys %old; # sort not needed, but nice touch :)
  close $out;
  }
[download]

https://www.perlmonks.org/?node_id=1208878