Padding an escape to fixed width?

[Aaron Davies]

What's the right invocation to pad a string escape to a specific fixed
width? e.g. if i want the hostname in a 10-character field (because my
network has hostnames of variable length, but a known max of ten, and
I want the rest of my caption to line up the same no matter what host
I'm on), what sort of %= do I wrap around the %H?

-- 
Aaron Davies
address@hidden