martin@martin:~$ whois seznam.cz
%  (c) 2006-2014 CZ.NIC, z.s.p.o.
% 
% Intended use of supplied data and information
% 
% Data contained in the domain name register, as well as information
% supplied through public information services of CZ.NIC association,
% are appointed only for purposes connected with Internet network
% administration and operation, or for the purpose of legal or other
% similar proceedings, in process as regards a matter connected
% particularly with holding and using a concrete domain name.
% 
% Full text available at:
% http://www.nic.cz/page/306/intended-use-of-supplied-data-and-information/
% 
% See also a search service at http://www.nic.cz/whois/
% 
% 
% Whoisd Server Version: 3.9.0
% Timestamp: Wed May 21 13:07:18 2014

domain:       seznam.cz
registrant:   SB:SEZNAM-CZ-AS
admin-c:      SB:SEZNAM-CZ-AS
nsset:        SEZNAM-NAMESERVERS
registrar:    REG-IGNUM
registered:   07.10.1996 02:00:00
changed:      23.01.2008 18:51:04
expire:       29.10.2014

contact:      SB:SEZNAM-CZ-AS
org:          Seznam.cz, a.s.
name:         Seznam.cz, a.s.
address:      Radlická 3294/10
address:      Praha 5
address:      15000
address:      CZ
e-mail:       domeny@firma.seznam.cz
registrar:    REG-IGNUM
created:      10.08.2001 22:13:00
changed:      17.06.2013 12:21:03

nsset:        SEZNAM-NAMESERVERS
nserver:      ns.seznam.cz (77.75.73.77, 2a02:598:1::1077)
nserver:      ms.seznam.cz (77.75.77.77, 2a02:598:2::1077)
tech-c:       SB:SEZNAM-CZ-AS
registrar:    REG-IGNUM
created:      18.10.2007 18:01:01
changed:      06.03.2012 15:37:03


martin@martin:~$ whois fb2m4e85r36z54jrbnk.cz
%  (c) 2006-2014 CZ.NIC, z.s.p.o.
% 
% Intended use of supplied data and information
% 
% Data contained in the domain name register, as well as information
% supplied through public information services of CZ.NIC association,
% are appointed only for purposes connected with Internet network
% administration and operation, or for the purpose of legal or other
% similar proceedings, in process as regards a matter connected
% particularly with holding and using a concrete domain name.
% 
% Full text available at:
% http://www.nic.cz/page/306/intended-use-of-supplied-data-and-information/
% 
% See also a search service at http://www.nic.cz/whois/
% 
% 
% Whoisd Server Version: 3.9.0

%ERROR:101: no entries found
% 
% No entries found.
martin@martin:~$

#!/bin/bash

UNAVAILABLE=nedostupne.txt
AVAILABLE=dostupne.txt
DOMAINS=domeny.txt

while read -r domain; do
  sleep 20
  whois $domain | grep -qci "No entries found"
  if [ $? == 0 ]; then
    # volna - hodnota grepu=0
    echo $domain >> $AVAILABLE
  else
    # obsazena - hodnota grepu=1
    echo $domain >> $UNAVAILABLE
  fi
done < $DOMAINS

Ukazka vstupniho souboru domeny.txt:

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

/**
 * @author http://codereview.stackexchange.com/questions/41510/calculate-all-possible-combinations-of-given-characters
 */
public class Kombinace {
	
	public static int pocet = 0;
	
	static File file = new File("/tmp/domeny.txt");
	static FileWriter fw;
	static BufferedWriter bw;
		
	public static void main(String[] args) throws IOException {
		
		fw = new FileWriter(file.getAbsoluteFile());
		bw = new BufferedWriter(fw);

		// Create an alphabet to work with
		char[] alphabet = new char[] { 
				'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A',
				'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
				'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
				'X', 'Y', 'Z'
				};
		// Find all possible combinations of this alphabet in the string size of
		// 3
		StringExcersise.possibleStrings(3, alphabet, "");		
		System.out.println("\n"+pocet);		
		bw.close();
	}

}

class StringExcersise {
	

	public static void possibleStrings(int maxLength, char[] alphabet,
			String curr) throws IOException {
		// If the current string has reached it's maximum length
		if (curr.length() == maxLength) {
			Kombinace.pocet++;		

			// Else add each letter from the alphabet to new strings and process
			// these new strings again
		} else {
			for (int i = 0; i < alphabet.length; i++) {
				String newCurr = curr + alphabet[i];
				Kombinace.bw.write(newCurr + ".cz" + '\n');
				possibleStrings(maxLength, alphabet, newCurr);
			}
		}
	}
}

Pouziti:

javac Kombinace.java
java Kombinace

Vyldedkem je vygenerovany soubor /tmp/domeny.txt.

Cele skenovani zony mozna neni uplne v souladu s podminkami spravce domeny, proto berte navod jen jako vzdelavaci pomucku 😉