# knitr Reference Card

## Yihui Xie

### 2025-12-19

## 1 Syntax

format | start | end | inline | output
--- | --- | --- | --- | ---
Rnw | `<<*>>=` | `@` | `\Sexpr{x}` | TeX
Rmd | ````{r *}` | ````` | ``r x`` | Markdown
Rhtml | `<!--begin.rcode *` | `end.rcode-->` | `<!--rinline x-->` | HTML
Rrst | `.. {r *}` | `.. ..` | `:r:`x`` | reST
Rtex | `% begin.rcode *` | `% end.rcode` | `\rinline{x}` | TeX
Rasciidoc | `// begin.rcode *` | `// end.rcode` | `+r x+` | AsciiDoc
Rtextile | `### begin.rcode *` | `### end.rcode` | `@r x@` | Textile
brew |  |  | `<% x %>` | text

`*` denotes local chunk options, e.g., `<<label, eval=FALSE>>=`; `x` denotes inline R code, e.g., ``r 1+2``.

## 2 Minimal Examples

### 2.1 Sweave (*.Rnw)

    \documentclass{article}
    \begin{document}

    Below is a code chunk.

    <<foo, echo=TRUE>>=
    z = 1 + 1
    plot(cars)
    @

    The value of z is \Sexpr{z}.
    \end{document}

### 2.2 R Markdown (*.Rmd)

    ---
    title: "An R Markdown document"
    ---

    Hi _Markdown_!

    ```{r foo, echo=TRUE}
    z = 1 + 1
    plot(cars)
    ```

    The value of z is `r z`.

## 3 Chunk Options

`opts_chunk` controls global chunk options, e.g., `knitr::opts_chunk$set(tidy = FALSE)`, which can be overridden by local chunk options. See all options at https://yihui.org/knitr/options/. Some frequently used options are:

- `eval`: whether to evaluate the chunk
- `echo`: whether to echo source code
- `results`: `'markup'`, `'asis'`, `'hold'`, `'hide'`
- `tidy`: whether to reformat R code
- `cache`: whether to cache results
- `fig.width`, `fig.height`, `out.width`, `out.height`: device and output size of figures
- `include`: whether to include the chunk results in output
- `child`: path to child documents
- `engine`: language name (R, python, …)

## 4 Functions

- `knit()`: the main function in this package; knit input document and write output
- `purl()`: extract R code from an input document
- `spin()`: spin goat’s hair (an R script with roxygen comments) into wool (a literate programming document to be passed to `knit()`)
- `stitch()`: insert an R script into a template and compile the document
- `knit_hooks$set()`: set or reset chunk and output hooks

## 5 Resources

- Homepage: https://yihui.org/knitr/
- Github: https://github.com/yihui/knitr (CRAN)
- Examples: https://github.com/yihui/knitr-examples
- Stack Overflow: https://stackoverflow.com/tags/knitr/