code for http://stackoverflow.com/questions/14587381/how-can-i-add-an-roxygen-export-all-functions-in-a-package

add @export

for( file in list.files("./R", full.names = TRUE)) {
  doc <- scan( what=character(), sep="\n", file, blank.lines.skip = FALSE))
  returns <- which(!grepl("returnItem", doc)  & grepl("@return", doc))
  if(length(returns) > 0){
    doc[returns] <- gsub("##' @return", paste("##' @export\n##' @return"), doc[returns])
    doc <- paste(doc, collapse="\n")
    cat(doc, file = file)
    
  }
}

Slightly cleaner, keeps contents of @return:

for( file in list.files("./R", full.names = TRUE) ) {
  doc <- scan( what=character(), sep="\n", file )
  doc <- gsub("##' @return (.*)", "##' @export\n##' @return \\1", doc)
  doc <- paste(doc, collapse="\n" )
  cat( doc, file=file )
}

Although ideally, we would want to ensure we don't already have an @export statement somewhere in the block, and that's a more difficult problem...