R Programming -- 2

i need a cmd based program in R that takes user input and based on user input it goes inside the csv file read those input user value as column and then check in those column any NA, unknown values are present or not. if yes then we need to change Na, unknown to 1900-01-01 in the same file and then if there is any field having datetime, need to split into two new columns i.e. Date and time