title: Grep and print back reference
body: <p>I have this iptable log:</p>
  
  <pre><code>Feb 25 10:32:48 XXX: [414645.555838] FW: DEN TCP IN=eth0 OUT= MAC=XYZ SRC=1.1.1.1 DST=2.2.2.2 LEN=40 TOS=0x00 PREC=0x00 TTL=57 ID=0 DF PROTO=TCP SPT=80 DPT=51814 WINDOW=0 RES=0x00 RST URGP=0
  </code></pre>
  
  <p>I want to grep 1.1.1.1 and 80 (SRC and SPT field). 
  I do this:</p>
  
  <pre><code>grep -oP 'SRC=([^ ]+).+SPT=([0-9]+)' /var/log/iptables.log
  </code></pre>
  
  <p>But it returns:</p>
  
  <pre><code>SRC=1.1.1.1 DST=2.2.2.2 LEN=40 TOS=0x00 PREC=0x00 TTL=57 ID=0 DF PROTO=TCP SPT=80
  </code></pre>
  
  <p>How do I get $1 and $2 only ( reference to the matched value)?</p>