* .global makes vdd reachable inside subckts without a port
.global vdd
Vdd vdd 0 DC 5
X1 in out amp
Vin in 0 DC 1
.subckt amp i o
  R1 i o 1k
  R2 o vdd 3k        $ vdd used here is the GLOBAL node
.ends
.tran 1u 5u
.control
  run
  print v(out)[0]    $ node balances between Vin=1 and global vdd=5
.endc
.end