gistfile1.sh

df | awk 'NR==1; NR > 1 {print $0 | "sort -nr -k2 -T ."}' | awk '{ print $6 }' | head -2 | tail -1

$> df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             9.7G  3.3G  6.0G  35% /
/dev/sda2             253G  3.0G  237G   2% /local
tmpfs                 7.9G     0  7.9G   0% /dev/shm

$> df | awk 'NR==1; NR > 1 {print $0 | "sort -nr -k2 -T ."}' 
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2            264342512   3118704 247579404   2% /local
/dev/sda1             10153988   3356244   6273628  35% /
tmpfs                  8218076         0   8218076   0% /dev/shm

$> df | awk 'NR==1; NR > 1 {print $0 | "sort -nr -k2 -T ."}' | awk '{ print $6 }'
Mounted
/local
/
/dev/shm

$> df | awk 'NR==1; NR > 1 {print $0 | "sort -nr -k2 -T ."}' | awk '{ print $6 }' | head -2 | tail -1
/local