Evaluation of the R code in the YAML header

Question

Consider the following Rmd file,

---
title: "Untitled"
author: "baptiste"
date: "`r Sys.Date()`"
output: html_document
test: "`r paste('_metadata.yaml')`"
---

```{r}
cat(rmarkdown::metadata$test)
```

The date is processed (knitted) by R before passing pandoc to convert to md and html. However, a custom field is testnot evaluated.

Who cares? Is it possible to get knitr / rmarkdown to evaluate an arbitrary field in the yaml header?

Note. The actual goal is not just print()the file name, as in this example, but to load the external yaml file containing metadata (information about the author), process it with R and display the line that will be entered in the document.

Answer 1

He evaluates the code. If you run foo.Rmd with

rmarkdown::render("foo.Rmd", clean = FALSE)

( pandoc) foo.knit.md . :

---
title: "Untitled"
author: "baptiste"
date: "2017-08-12"
output: html_document
test: "_metadata.yaml"
---


```r
cat(rmarkdown::metadata$test)
```

```
## `r paste('_metadata.yaml')`
```

, ( , metadata$test ), , , - , .

Answer 2

data test . :

---
title: "Untitled"
author: "baptiste"
date: "`r Sys.Date()`"
output: 
  html_document: 
    keep_md: yes
test: "`r paste('_metadata.yaml')`"
---

```{r}
cat(rmarkdown::metadata$date)
cat(rmarkdown::metadata$test)
```

:

, date . rmarkdown knitr. :

---
title: "Untitled"
author: "baptiste"
date: "`r Sys.Date()`"
output: 
  html_document: 
    keep_md: yes
test: "`r paste('_metadata.yaml')`"
---

```{r}
eval_meta <- function(x) eval(parse(text = gsub("`|r", "", x)))
eval_meta(rmarkdown::metadata$date)
eval_meta(rmarkdown::metadata$test)
```

, , .