add " " before ```

jekyll.R

#! /usr/bin/Rscript
# convert from:
#
# ```
# xxxxx....
# ```
#
# to:
#
# ```txt
# xxxxx....
# ```

argv <- commandArgs(TRUE)

src <- readLines(argv[1])

is_code_block <- FALSE

greg.result <- gregexpr(pattern="^(\\s{4})*```(?<decorator>.*)$", text=src, perl=TRUE)
match.index <- which(unlist(greg.result) == 1)
for(i in match.index) {
	if (!is_code_block) {
		if (attr(greg.result[[i]], "capture.length")[1,"decorator"] == 0) src[i] <- sub(pattern="```", replacement="```txt", x=src[i])
	}
	is_code_block <- !is_code_block
}

write(src, file=argv[1])