Validate output filepath at the start of the process

[ecroot]

Hi, I've just started using this tool and think it's great!
When supplying a file path for the output file (I didn't want the output file to be placed in the working directory), the command runs to 100% completion (taking a few minutes) before returning a "cannot create file", "No such file or directory" error.
I am not an expert in R, but I know that it would be simple to validate the supplied file path at the start of a process in Python. If the same is true for R, I think it would vastly improve user experience to get the directory errors at the start of the process rather than waiting for it to finish.