In interactive mode, this functions asks the user to type the value of a given variable. In non-interactive mode, it searchs the value in the command line arguments and it returns an error if the value does not exist.
requireVariable(name, desc = NULL, default = NULL,
what = character(), nmax = 1, alwaysAsk = TRUE, env = .GlobalEnv)
Name of the required variable
Description to display
Default value for the variable
Type of data to read in interactive mode.
Number of values to read in interactive mode.
If the variable already exists, should the function ask a new value?
Environment where the variable should be defined
Used for side effects