Best way to extract number of partitions?

Question

Assuming that there are only primary partitions on a disk, what is the best way to find the current number of partitions?

Is there any better way than:

fdisk -l > temp
#Following returns first column of the last line of temp e.g. /dev/sda4
lastPart=$(tail -n 1 temp | awk '{print $1}')
totalPartitions=$(echo ${lastPart:8})

$totalPartitions variable sometimes returns NULL. That's why, I was wondering if there is a more reliable way to find the current number of partitions.

Answer 1

What about:

totalPartitions=$(grep -c 'sda[0-9]' /proc/partitions)

?