With or without formatting the drive? What partition map are you using as the live resizing feature only works with GPT (GUID Partition Table) which is the default if you have an Intel Mac.
It is possible to resize an HFS+ drive from the command line using
diskutil or by using Disk Utility. In Disk Utility you can resize the partition using the resize scrubber (the the diagonal lines in the bottom right corner of the partition) (Example).
If you want to do it via the command line you're looking for the command
resizeVolume as part of
diskutil. This will non-destructively resize a disk so long as you have space available. It may be necessary to defrag your disk before this is possible if your disk is relatively full.
diskutil resizeVolume disk0s2 10G JHFS+ 10G JHFS+ (Creates two partitions of 10GB apiece formatted as Journaled HFS+ systems).
You can find more by running
diskutil resizeVolume. It should go without saying that you should have a backup just in case something goes wrong.