🕵️‍♂️ RegExplain

An RStudio addin slash utility belt for regular expressions

April 3, 2018

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Regular expressions are tricky. RegExplain makes it easier to see what you’re doing.

RegExplain is an RStudio addin slash utility belt for regular expressions. Interactively build your regexp, check the output of common string matching functions, consult the interactive help pages, or use the included resources to learn regular expressions. And more.

Inspired by RegExr.com and stringr::str_view().


Installation is easy with devtools


or for hands-free installation


Try it out!

#| standalone: true
#| components: [viewer]
#| viewerHeight: 550

if (!requireNamespace("regexplain", quietly = TRUE)) {
  install.packages("regexplain", repos = c(


  ui = regexplain:::regexplain_gadget_ui(),
  server = regexplain:::regexplain_gadget_server(NULL)

The demo version of regexplain is running in your browser, thanks to shinylive for Quarto, r-wasm, and WASM binaries provided by r-universe.dev. You can also view the app in a separate window thanks to shinylive.io.

RegExplain in Action


RegExplain Selection

Regular Expressions Library

RegExplain Library

Try the Built-In Examples

RegExplain Examples

RStudio Addin

The main feature of this package is the RStudio Addin RegExplain Selection. Just select the text or object containing text (such as the variable name of a vector or a data.frame column) and run RegExplain Selection from the RStudio Addins dropdown.

regexplain in the Rstudio Addins dropdown

The addin will open an interface with 4 panes where you can

  • edit the text you’ve imported
  • build up a regex expression and interactively see it applied to your text
  • test the output of common string matching and replacement functions from base and stringr
  • and refer to a helpful cheatsheet

 The panes of regexplain

When you’re done, click on the Send Regex to Console to send your regex expression to… the console!

> pattern <- "\\b(red|orange|yellow|green|blue|purple|white|brown)(?:\\s(\\w+))?"

Notice that RegExplain handled the extra backslashes needed for storing the RegEx characters \b, \s, and \w. Inside the gadget you can use regular old regular expressions as you found them in the wild (hello, Stack Overflow!).

Help and Cheat Sheet

The Help tab is full of resources, guides, and R packages and includes an easy-to-navigate reference of commonly used regular expression syntax.

 regexplain help windows

Open RegExplain Cheatsheet from the RStudio Addins drop down to open the regex reference page in the Viewer pane without blocking your current R session.

Import Your Text

There are two ways to get your text into RegExplain. The first way was described above: select an object name or lines of text or code in the RStudio source pane and run RegExplain Selection. To import text from a file, use RegExplain File to you import the text you want to process with regular expressions.

When importing text, RegExplain automatically reduces the text to the unique entries and limits the number of lines.

 regexplain addins

Regular Expressions Library

The RegExplain gadget includes a regular expressions library in the RegEx tab. The library features common regular expressions, sourced from qdapRegex and Regex Hub, with several additional patterns.

The full library is stored as a JSON file in inst/extdata/patterns.json, feel free to contribute patterns you find useful or use regularly via pull request.

 regexplain library modal

View Static Regex Results

RegExplain provides the function view_regex() that you can use as a stringr::str_view() replacement. In addition to highlighting matched portions of the text, view_regex() colorizes groups and attempts to colorize the regex expression itself as well.

text <- c("breakfast=eggs;lunch=pizza",
          "no food here")
pattern <- "((\\w+)=)(\\w+).+(ch=s?p)"

view_regex(text, pattern)

 Example view_regex(text, pattern).

t_nested <- "anestedgroupwithingroupexample"
r_nested <- "(a(nested)(group(within(group))(example)))"
view_regex(t_nested, r_nested)

 Example of nested groups


Regular expressions are nothing if not a collection of corner cases. Trying to pass regular expressions through Shiny and HTML inputs is a bit of a labyrinth. For now, assume any issues or oddities you experience with this addin are entirely my fault and have nothing to do with the fine packages this addin is built on. If you do find an issue, please file an issue. Pull requests are welcomed!