You have an array of IP addresses but are only interested in the unique values. Since perl doesn't have a unique() function, we'll exploit the concept of unique keys in hashes:

#!/usr/bin/perl

my @ipAddresses = ('192.168.0.1', '192.168.0.27',
                   '192.168.0.1', '192.168.0.3');
print "Before: ", qq(@ipAddresses), "\n";

undef %saw;
@saw{@ipAddresses} = ();
@sorted = sort keys %saw;

print "After : ", qq(@sorted), "\n";

Resulting in:

Before: 192.168.0.1 192.168.0.27 192.168.0.1 192.168.0.3
After : 192.168.0.1 192.168.0.3 192.168.0.27