title: Grep on a single column in Linux
body: <p>I'm trying to parse <code>df -h</code> command's output. For example:</p>
  
  <pre><code>Filesystem            Size  Used Avail Use% Mounted on
  /dev/mapper/VGExaDb-LVDbSys1
                         30G   17G   12G  58% /
  /dev/sda1             496M   38M  433M   8% /boot
  /dev/mapper/VGExaDb-LVDbOra1
                         99G   18G   76G  19% /u01
  tmpfs                 252G   90M  252G   1% /dev/shm
  dbfs-dbfs_user@:/     4.0T  283G  3.7T   8% /dbfs_direct
  </code></pre>
  
  <p>I only want values under "Avail" column. But <code>awk</code> command doesn't work as i wanted, because number of words in each line is not the same. When i run <code>df -h | awk '{print $4}'</code> command, it gives the output like this:</p>
  
  <pre><code>Avail
  
  58%
  433M
  
  19%
  252G
  3.7T
  </code></pre>