Save bash code chunks in R Markdown documents into separate script files

bash.Rmd

---
output: html_document
---

```{r setup, include=FALSE}
knit_hooks_source <- knitr::knit_hooks$get("source")
knitr::knit_hooks$set(source = function (x, options) {
  if (!is.null(options$save))
    writeLines(x, options$save)
  knit_hooks_source(x, options)
})
knitr::opts_hooks$set(engine = function(options) {
  if (options$engine == "bash") {
    options$eval <- FALSE
    options$save <- paste0(options$label, ".sh")
  }
  options
})
```

```{bash hello}
#!/bin/bash
echo "Hello World!"
```