If, for some reason, you want to spread your PLUMED input over a number of files you can use INCLUDE as shown below:
INCLUDE FILE=filename
So, for example, a single "plumed.dat" file:
DISTANCE ATOMS=0,1 LABEL=dist RESTRAINT ARG=dist
could be split up into two files as shown below:
DISTANCE ATOMS=0,1 LABEL=dist INCLUDE FILE=toBeIncluded.dat
plus a "toBeIncluded.dat" file
RESTRAINT ARG=dist
However, when you do this it is important to recognise that INCLUDE is a real directive that is only resolved after all the Comments have been stripped and the Continuation lines have been unrolled. This means it is not possible to do things like:
# this is wrong: DISTANCE INCLUDE FILE=options.dat RESTRAINT ARG=dist