Let's take a look at the following steps to learn how to use a regular expression in text processing:

1. To read the text from an URL, first, you need to create a connection between your R session and the web page.
2. Note that your computer must be connected to the internet to run this recipe. Once you have connected and created the connection of R session, you are ready to retrieve the HTML code form of the page. Here is the code to do the whole thing:

        sourceURL <- 
        "https://en.wikipedia.org/wiki/Programming_with_Big_Data_in_R"
        link2web <- url(sourceURL)
        htmlText <- readLines(link2web)
        close(link2web)

3. Now you have the HTML text in an object called htmlText. This object contains plain text as well as HTML tag pairs. The task is to remove all HTML tags, punctuation, and numbers using a regular expression as follows:

        # Remove html tags
        htmlText = gsub("<.*?>", "", htmlText)
        # remove puntuation
        htmlText = gsub("[[:punct:]]", " ", htmlText)
        # remove numbers  
        htmlText <- gsub('\d+', '', htmlText)