We have a process here were users must push files onto USB disks. The
user logs in remotely to a machine which may have many USB disks
attached and he/she knows the serial number of the disk to write to.

In trying to do away with some complex, hacky scripts I'm trying to
udev-ise this. Ie. when a USB disk is plugged into the machine a symlink
to it is made that is /dev/disknumber-123456 where '123456' is the
serial number of the disk.

My udev rule is:
KERNEL=="sd*", SUBSYSTEMS=="scsi", SYMLINK+="disknumber-%E{serial}"
It can create devices with symlink '/dev/disknumber-' but the
substitution of the ATRR{serial} bit seems to be impossible to get working.

The man page is usual includes no examples which might actually give me
the context I need to properly understand the 'printf-like substitution'
syntax that the developers are talking about.

Tim Edwards