title: Trouble doing grep only 10 digit number from a file
body: <p>I am unable to grep exact only 10 digit number I wanted from a zone file.</p>
  
  <p>Example zone file is:</p>
  
  <pre><code>&gt; cat /var/named/test.com.db
  ; cPanel first:11.11.0-BETA_16994 (update_time):1468656855 Cpanel::ZoneFile::VERSION:1.3 hostname:server.test.com latest:11.56.0.13
  ; Zone file for test.com
  $TTL 14400
  test.com.      86400   IN      SOA     ns1.test.com.     cpanel.test.com.  (
                                                  2016071602 ;Serial Number
                                                  14400 ;refresh
                                                  7200 ;retry
                                                  2419200 ;expire
                                                  43200   )
  ; test.com.    86400   IN      SOA     ns1.test.com.       serveralerts.test.com.        ( ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;                                               2015061700 ;Serial Number ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;                                               86400 ;refresh ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;                                               7200 ;retry ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;                                               3600000 ;expire ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;                                               86400 ;minimum ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ;       ) ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  
  test.com.      86400   IN      NS      ns1.test.com.
  test.com.      86400   IN      NS      ns2.test.com.
  ; test.com.    86400   IN      NS      ns1.test.com. ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  ; test.com.    86400   IN      NS      ns2.test.com. ; Previous value removed by cPanel restore auto-merge on 20160510102706 GMT
  
  
  test.com.      14400   IN      A       192.168.1.100
  
  localhost       14400   IN      A       127.0.0.1
  
  test.com.      14400   IN      MX      0       test.com.
  
  mail    14400   IN      CNAME   test.com.
  www     14400   IN      CNAME   test.com.
  ftp     14400   IN      CNAME   test.com.
  webdisk 14400   IN      A       192.168.1.100
  cpcalendars     14400   IN      A       192.168.1.100
  test.com. IN TXT "v=spf1 +a +mx +ip4:192.168.1.100 ~all"
  </code></pre>
  
  <p>I want to see only the current serial number <strong>2016071602</strong> from the zone file on grep output.</p>
  
  <p>For that I tried the command:</p>
  
  <pre><code>grep -o '2016[0-9]\{6\}' /var/named/test.com.db
  </code></pre>
  
  <p>But it outputs all those trash. I meant even digits with length more than 10</p>
  
  <p>The result I am getting is:</p>
  
  <pre><code>&gt; grep -o '2016[0-9]\{6\}' /var/named/test.com.db                     
  2016071602
  2016051010
  2016051010
  2016051010
  2016051010
  2016051010
  2016051010
  2016051010
  2016051010
  2016051010
  </code></pre>
  
  <p>Could you help me to filter this out properly?. Once I able to correct this one, I will be happy to proceed with mass zones update on the server.</p>