Grep on a single column in Linux

Question

I'm trying to parse df -h command's output. For example:

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

I only want values under "Avail" column. But awk command doesn't work as i wanted, because number of words in each line is not the same. When i run df -h | awk '{print $4}' command, it gives the output like this:

Avail

58%
433M

19%
252G
3.7T

Answer 1

Try this:

df -Ph | awk '{ print $4 }'

Per man page:

   -P, --portability
          use the POSIX output format

This won't lead to unnecessary line breaks. h will give you in human readable format.