title: How can I *only* get the number of bytes available on a disk in bash?
body: <p><code>df</code> does a great job for an overview. But what if I want to set a variable in a shell script to the number of bytes available on a disk?</p>
  
  <p>Example:</p>
  
  <pre><code>$ df
  Filesystem            1K-blocks     Used Available Use% Mounted on
  /dev/sda             1111111111  2222222  33333333  10% /
  tmpfs                  44444444      555  66666666   1% /dev/shm
  </code></pre>
  
  <p>But I just want to return <code>33333333</code> (bytes available on <code>/</code>), not the whole <code>df</code> output.</p>