title: Linux use output command 1 in command 2
body: <p>I'm using <code>cat /sys/class/net/eth0/address</code> to find the mac address of my raspberry</p>
  
  <p>I need to use the output of <code>cat /sys/class/net/eth0/address</code> (the mac adress), in a new command.</p>
  
  <p>How can I do that?</p>