You're falling into a very common mistake made in dealing with IP addresses. They're actually just a 32 bit number that happen to be commonly written in a really wierd way - dotted quad notation. Use the functions inet_ntoa and inet_aton (perldoc Socket for details) to get them into numbers, and you can quickly and easily sort them properly in perl. If you try to sort them with sort -u, then you'll have problems. For example, '10' will get placed before '5'. First, to get all of the IP addresses out of a text file, use a loop something like this (note that this assumes that there is at most one IP address per line)

my $ips;
while(<INPUT>){
    if (/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/{
        push @ips, $1;
    }
}
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You don't really say what you IP range is, but I'll use for example the network 192.168.20.0 with a netmask of 255.255.255.0. This will weed out addresses only in this network, sort them numerically, and print them out.

use Socket;
my $mask = 24; # 255.255.255.0 -> 24 bit netmask
my $network = inet_aton("192.168.20.0");

my @myips;

foreach $ip ( @iplist ) {
    $ip = inet_ntoa($ip); # convert ascii to decimal
     if( ($ip & $mask) == ($network & $mask) ){
        push @myips, $ip;
    }
}
# this will sort the list properly since it's sorting the numbers.
# otherwise it would sort 192.168.20.20 before 196.168.20.3
@myips = sort @myips;
foreach $ip ( @myips ) {
    # print out the ascii format
    print inet_ntoa($ip), "\n";
}
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