As near as I can tell, you want somehting like this:

#!/usr/bin/perl -w

use Data::Dumper;

while(<DATA>)
{
    chomp;
    next unless $_;
    if($_ =~ /^\d+\.\d+\.\d+\.\d+/) 
    {
        push @{$CoreRegR{$key}},$_;
        # first time, for new server, auto-vivifies
        # $CoreRegR{$key} as arrayref.        
        # first and all other times,        
        # pushes the ip range onto the anon array that
        # $CoreRegR{$key} refers to.
    }
    else 
    {
        $key = $_;
    } 
}

print Dumper(\%CoreRegR);

__DATA__
Server1 Name
192.168.100.1/27
192.168.101.2/32
Server2 Name
Server3 Name
192.168.102.3/31
192.168.103.4/30
192.168.104.5/28
Server4 Name
10.100.2.1/31
10.101.2.2/32
10.102.2.3/28
Server5 Name
10.103.2.4/29
10.104.2.5/27
[download]

which produces this output:

$VAR1 = {
          'Server3 Name' => [
                              '192.168.102.3/31',
                              '192.168.103.4/30',
                              '192.168.104.5/28'
                            ],
          'Server4 Name' => [
                              '10.100.2.1/31',
                              '10.101.2.2/32',
                              '10.102.2.3/28'
                            ],
          'Server5 Name' => [
                              '10.103.2.4/29',
                              '10.104.2.5/27'
                            ],
          'Server1 Name' => [
                              '192.168.100.1/27',
                              '192.168.101.2/32'
                            ],
          'Server2 Name' => []
        };
[download]

Although I use 'unless' in modifiers (as in above, next unless $_), I find it hard to think about full blown unless-else constructs - maybe that's just me, but my head gets all tangled up.

As noted by a previous poster, use Data::Dumper - it is invaluable in figuring out what is going on.

Update: fixed where I called an arrayref a hashref wrongly.

--Bob Niederman, http://bob-n.com

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