OK, this is the original script:
! OPEN FILES, FILL SERIES VIA TRAJ
set k = @FF
set u = 8
open read unit @U file name @S/dyn@K.trj
incr u by 1
incr k by 1
if k le @LF goto opnlp
traj firstu 8 nunit @N
I see here a loop to merge several trajectory files. In my case I don't have several trajectory file to merge. I have only one file, popclipidsnowater.dcd.
I don't see other command besides "open read unit @U file name @S/dyn@K.trj"
What am I missing?