prtpicl -v \
| egrep ':disk0.*/pci[^/]+/pci[^/]+/pci[^/]+/scsi[^/]+/disk' \
| awk '{print $2}'
Por exemplo
$ cat prtpicl.out
Some headings blah blah
:disk0 some uninteresting stuff
:disk0 /pci@0/pci@0/pci@2/scsi@0/disk@0
:disk1 /pci@0/pci@0/pci@2/scsi@0/disk@1
Last line
$ cat prtpicl.out \
> | egrep ':disk0.*/pci[^/]+/pci[^/]+/pci[^/]+/scsi[^/]+/disk' \
> | awk '{print $2}'
/pci@0/pci@0/pci@2/scsi@0/disk@0