Shell Script to read capacity of partition (Android)

I need a script that can read capacity of partition, for example i want to read capacity of /cache partition

Maybe you can give me if-statement to make some optional i think like this

if /cache partition at 32-63mb then paste 1.sh in /system/etc/init.d
else if /cache partition at 64-128mb then paste 2.sh in /system/etc/init.d
else paste 3.sh in /system/etc/init.d

I need a shell script for Android