Read a Line from the Terminal
DESCRIPTION:
Returns a character string which is one line of input.
USAGE: 
readline()
VALUE:
character string giving the line read from the terminal. This contains all of the characters typed prior to an <enter> or <return>.
DETAILS:
This is useful in writing S-PLUS functions that interact with the user.
EXAMPLES: 
cat("Do you want to continue? ")
ans <- readline()
if(ans=="n" || ans=="no") return()


reply <- readline()
if (nchar(reply) == 0) break else reply <- as.numeric(reply)