If, for some reason, you want to spread your PLUMED input over a number of files you can use INCLUDE as shown below:

Click on the labels of the actions for more information on what each action computes

INCLUDE FILEcompulsory keyword 
file to be included =filename  You cannot view the components that are calculated by each action for this input file. Sorry

So, for example, a single "plumed.dat" file:

Click on the labels of the actions for more information on what each action computes

dist: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2 The DISTANCE action with label dist calculates a single scalar value
RESTRAINT ARGthe arguments on which the bias is acting. =dist ATcompulsory keyword 
the position of the restraint =2.0 KAPPAcompulsory keyword ( default=0.0 )
specifies that the restraint is harmonic and what the values of the force constants
on each of the variables are =1.0 The RESTRAINT action with label

dist: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2 The DISTANCE action with label dist calculates a single scalar value

could be split up into two files as shown below:

Click on the labels of the actions for more information on what each action computes

dist: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2 The DISTANCE action with label dist calculates a single scalar value
INCLUDE FILEcompulsory keyword 
file to be included =toBeIncluded.inc The INCLUDE action with label

plus a "toBeIncluded.inc" file

Click on the labels of the actions for more information on what each action computes

#SETTINGS FILENAME=toBeIncluded.inc
# this is toBeIncluded.inc
RESTRAINT ARGthe arguments on which the bias is acting. =dist ATcompulsory keyword 
the position of the restraint =2.0 KAPPAcompulsory keyword ( default=0.0 )
specifies that the restraint is harmonic and what the values of the force constants
on each of the variables are =1.0  You cannot view the components that are calculated by each action for this input file. Sorry

However, when you do this it is important to recognize 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:

Click on the labels of the actions for more information on what each action computes

# this is wrong:
DISTANCE INCLUDE could not find this keyword  FILE could not find this keyword =options.dat  You cannot view the components that are calculated by each action for this input file. Sorry 
RESTRAINT ARGthe arguments on which the bias is acting. =dist ATcompulsory keyword 
the position of the restraint =2.0 KAPPAcompulsory keyword ( default=0.0 )
specifies that the restraint is harmonic and what the values of the force constants
on each of the variables are =1.0  You cannot view the components that are calculated by each action for this input file. Sorry