[R] problem with creating a netcdf file under script sh

[Tu Anh Tran]

Hi everyone, 
I try to make a netcdf file which disposes a difference between 2 variables of 2netcdf files same dimension 
When I programmed under R, everything is ok but when I put the code under EOF of a sh script, an error occurs: 
"Error, passed variable has a dim that is NOT of class dim.ncdf!". My programme is: 

x1<-open.ncdf("file1.nc") 
x2<-open.ncdf("file2.nc") 
y1<-get.var.ncdf(x1,"a") 
y2<-get.var.ncdf(x2,"a") 
y<- y1-y2 
t<-var.def.ncdf("t",units="c",dim=x1$dim,-1) 
nc<-create.ncdf("test.nc",vars=t) 
put.var.ncdf(nc,t,y) 
close.ncdf(nc) 

Thanks in advance, 
T.A