Printing row with highest value

Question

Given following output derived from df -P | awk '!/udev|boot|tmpfs|none/ && NR>1 {printf ("%-10s\t%-10s\t%-10s\n", $1, $2, $6)}' | grep -wv /.

/dev/sda2       576075280       /hdd
/dev/sda1       1344681704      /home
/dev/vda2       2468687261      /media/user/backup
/dev/vda1       823581356       /media/user/movie
/dev/sdb2       676075280       /media/user/db2
/dev/sdb1       1691481049      /media/user/db1

I want to select row with largest storage from each partition, the desired output would be.

/dev/sda1       1344681704      /home
/dev/vda2       2468687261      /media/pi/backup
/dev/sdb1       1691481049      /media/pi/db1

Answer 1

In Linux you can just use lsblk instead of df for finding the biggest partition of each disk:

lsblk -nPpbo KNAME,SIZE,PKNAME,MOUNTPOINT |

awk -F'="|" ?' -v OFS='\t' '
    {
        kname = $2       # device name, for ex. /dev/sda1
        size = $4        # size of the device, in Bytes
        pkname = $6      # parent device name, for ex. /dev/sda 
        mountpoint = $8  # where the device is mounted, absolute path
    }

    pkname !~ "^/" { next }
    mountpoint !~ "^/" { next }
    mountpoint == "/" { next } # not sure why you want to exclude /

    size > sizes[pkname] {
        knames[pkname] = kname
        sizes[pkname] = size
        mountpoints[pkname] = mountpoint
    }

    END {
        for (pkname in knames)
            print knames[pkname], sizes[pkname], mountpoints[pkname]
    }
'

^{remark: the size will be displayed in Bytes instead of 512 or 1024 blocks, and possibly problematic characters in the fields (mostly in the mount point) will be escaped with a two digits hexadecimal notation \xHH. IMHO both of those are good points because you'll be able to read and unescape the resulting TSV accurately with bash.}

---

Here are the relevant options taken from lsblk documentation:

-b, --bytes
       Print the SIZE column in bytes rather than in a human-readable format.
-n, --noheadings
       Do not print a header line.
-P, --pairs
       Produce output in the form of key="value" pairs.
       All potentially unsafe characters are hex-escaped (\x<code>).
-p, --paths
       Print full device paths.
-o, --output list
       Specify which output columns to print. [...]

       KNAME internal kernel device name
       MOUNTPOINT where the device is mounted
       SIZE size of the device
       PKNAME internal parent kernel device name