R/write_lines_to_file.R

In dockr: Creation of Lightweight Docker Images for Your Packages

#' Write Lines to File
#'
#' @param lines \code{character} lines that will be written to file.
#' @param filepath \code{character} filepath of file to write lines to.
#' @param prepend \code{logical} should the new lines be prepended to
#' the existing text? Defaults to FALSE, which implies that the new lines will
#' be appended.
#' @param print_file \code{logical} should the contents of the file be printed
#' after editing? Defaults to TRUE.
#'
#' @return invisible return. Lines will be written to file as side effects to
#' function call.
#'
#' @export
#' 
#' @examples
#' # create empty file.
#' fp <- file.path(tempdir(), "dummy")
#' file.create(fp)
#' 
#' # append lines to Dockerfile.
#' write_lines_to_file(c("# dummy line 1", "# dummy line 2"), 
#' filepath = fp)
#' 
#' # prepend lines to Dockerfile.
#' write_lines_to_file(c("# dummy line 3", "# dummy line 4"), 
#' filepath = fp, prepend = TRUE)
write_lines_to_file <- function(lines,
                                filepath = "",
                                prepend = FALSE,
                                print_file = TRUE) {

  # validate inputs.
  if (!is.character(lines)) {
    stop("'lines' must be a character vector.")
  }

  if (!length(lines) > 0) {
    stop("'lines' must have a positive length.")
  }

  if (prepend) {
    # read existing contents of file.
    text <- readChar(filepath, file.info(filepath)$size)
    text <- strsplit(text, "\r\n")
    text <- unlist(text)
    # write lines plus existing contents to file.
    write(unlist(c(lines, text)),
          filepath,
          append = FALSE)
  } else {
    # append new lines to file.
    write(lines,
          filepath,
          append = TRUE)
  }

  # print resulting file.
  if (print_file) {
    print_file(filepath)
  }

  # return invisibly.
  invisible(NULL)

}