docopt.R demo

gistfile1.txt

#!/usr/local/bin/Rscript

'usage: my_prog.R [-a -r -m <msg>]

options:
-a        Add
-r        Remote
-m <msg>  Message' -> doc

library(docopt)
opts <- docopt(doc)

system("touch alog.txt")
prev_msg <- readLines("alog.txt")

where <- if (opts[["-r"]]) "REMOTE: " else "LOCAL: "
msg <- if (!is.null(opts[["-m"]])) opts[["-m"]] else "<empty>"
final_msg <- c(prev_msg, paste0(where, msg))
if (opts[["-a"]]) cat(final_msg, file = "alog.txt", sep="\n", append = FALSE)
cat(final_msg, sep = "\n")

Example usage:

chmod +x file.R
./file.R 
./file.R -a -m 'hello'