An example R script that takes in 2 command line parameters, checks whether these 2 arguments are digits and then sums them.

cmd_line_param.R

#!/bin/env Rscript

#usage
usage <- 'Usage: cmd_line_param.R <integer_1> <integer_2>';

#store command line arguments
args <- commandArgs(trailingOnly = T)

#conditional checks
if (length(args) != 2){
   print(usage);
} else {
   #Perl regular expression for integers
   if (length(grep(pattern="^-*\\d+$",x=args,perl=T,value=T)) != 2){
      print(usage);
   } else {
      sum(as.numeric(args));
   }
}