disk=sda
[root@localhost monitor]# echo $disk
sda
[root@localhost monitor]# iostat | awk 'BEGIN{disk="'"$disk"'"}{if ($1==disk) print;}'
sda 0.15 0.12 3.90 307283 9924087
[root@localhost monitor]# iostat
Linux 3.10.0-862.el7.x86_64 (localhost.localdomain) 08/12/2020 _x86_64_ (32 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 0.00 0.00 0.00 99.99
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
fd0 0.00 0.00 0.00 8 0
sdb 0.00 0.00 0.00 6639 0
sda 0.15 0.12 3.90 307283 9924087
dm-0 0.26 0.11 3.85 277153 9800480
dm-1 0.00 0.00 0.00 3260 0