Handling Error Thrown After source(...), read.table(...), and readLines(...)

Finally, I'm getting to a point in working with R where I would like to start to add some smart and custom error handling.  

Specifically, I would like to add custom error handling to my code for source(...), read.table(...), and readLines(...)

For example, right now I have the following:

postprocesspath<-c("C:/")
postprocess_scriptname<-c("Bob.R")
fullpostpocessingpath<-paste(postprocesspath, postprocess_scriptname, sep="")
source(fullpostpocessingpath)

Error in file(file, "r", encoding = encoding) : 
  cannot open the connection
In addition: Warning message:
In file(file, "r", encoding = encoding) :
  cannot open file 'C:/Bob.R': No such file or directory


Instead of the error shown above, I would just like to simply have the last line "cannot open file 'C:/Bob.R': No such file or directory" Or, add my own statement to the above, e.g. 

##########################################################
##########################################################
[[elided Yahoo spam]]
##########################################################
##########################################################


I would like to do something similar for read.table(...) and readLines(...).


Is such a thing possible? 

Thanks again.