Demonstrate reading bibtex for Rmarkdown from the web (e.g., from github)

demo.R

# This file is to demonstrate the output. 
# It is not needed.

testRmd = "https://gist.githubusercontent.com/richarddmorey/c4dd7d1fba2aa055a6f71286baedac25/raw/c256dd9f1ca0b22dfbce12443e1cb98ed5bb9d86/demo.Rmd"

tf = tempfile(fileext = ".Rmd")
tf_out = tempfile(fileext = ".html")
cat(RCurl::getURL(testRmd), file = tf)


rmarkdown::render(tf,output_file = tf_out)
browseURL(tf_out)

demo.Rmd

---
title: "Test reading bibtex from web"
output: html_document
bibliography: "`r devtools::source_gist(id = 'c4dd7d1fba2aa055a6f71286baedac25', filename = 'getbib.R'); getbib()`"
---

You'll need the devtools package installed for this to work. Alternatively, you can save the `getbib.R` file locally to prevent loading the function from the internet every time. Then just use `source()` instead of `devtools::source_gist()` (I really only used `devtools::source_gist` so that it would work for this demo).

This is a test [@Fisher:1955].

# References

getbib.R

# This function does the work of loading the bibtex file from the web 
# and potentially saving it for offline use, refreshing it when it is too 
# old
getbib <- function(file_name = "references.bib", 
                   refresh_days = 0,
                   copy_to_current = FALSE, 
                   URL = "http://drsmorey.org/bibtex/bibfile.php")
{
  if( is.null(file_name) ){
    file_name <- tempfile(fileext = ".bib")
  }else if( file.exists(file_name) ){
    file_age = difftime(Sys.time(), 
                        file.mtime( file_name ), 
                        units = "days")
    if(file_age < refresh_days) return( file_name )
  }
  
  bib_content = RCurl::getURL(URL)
  # iconv(bib_content, from = "CP1252", to = "UTF-8")
  cat(bib_content, file = file_name)
  if(copy_to_current){
    file.copy( file_name, getwd() )
  }
  return(file_name)
}