The forward slash doesn't look like a legal character. However by mounting by label or uuid, the fstab entry will be valid even if you repartition the drive, or if the device is external and gets a different device node the next time you plug it in.
You can get the label, uuid and filesystem information using the "udevinfo" program. You don't need to run it as root.
For example, if you what the information for the device & filesystem for /dev/sda5:
udevinfo -q env -n /dev/sda5
There are other options besides (-n) such as for using the /sys/ filesystem, the that type of query doesn't use the /sys/ part of the directory name so tab completion doesn't work.