How do I knit to two formats simulateously with Quarto?

Question

Is it possible to create multiple output formats from a Quarto/R Markdown document at once by specifying them in the YAML header?

My guess did not work:

---
title: Stacked Area chart with Annotations
format: 
  - html
  - gfm
---

Answer 1

Try this way (and suppose file name is format_test.qmd)

format_test.qmd

---
title: "Untitled"
format:
  html: default
  gfm: default
---

## Quarto

Quarto enables you to weave together content and executable code
into a finished document. To learn more about Quarto 
see <https://quarto.org>.

## Running Code

When you click the **Render** button a document will 
be generated that includes both content and the output 
of embedded code. You can embed code like this:

```{r}
1 + 1
```

Then from console run this following code to generate both html and github flavoured markdown (gfm) file at once.

# install.packages("quarto")

quarto::quarto_render("format_test.qmd", output_format = "all")

Or if you prefer using the terminal (or if you are a non R-useR) you can run the following command in the terminal,

quarto render format_test.qmd --to html,gfm

Be careful to specify multiple formats without putting any space in between i.e. type them as html,gfm.

And running the above command in the terminal does not require you to specify format yaml option in your document. So, for

format_test.qmd

---
title: "Untitled"
---

## Quarto

Quarto enables you to weave together content and executable code
into a finished document. To learn more about Quarto 
see <https://quarto.org>.

---

quarto render format_test.qmd --to pdf,html,gfm

---

will generate three files in HTML, pdf, and markdown format.