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Exercise

Matching any character

In a regular expression you can use a wildcard to match a single character, no matter what the character is. In rebus it is specified with ANY_CHAR. Try typing ANY_CHAR in the console. You should see that in the regular expression language this is specified by a dot, ..

For example, "c" %R% ANY_CHAR %R% "t" will look for patterns like "c_t" where the blank can be any character. Consider the strings: "cat", "coat", "scotland" and "tic toc". Where would the matches to "c" %R% ANY_CHAR %R% "t" be?

Test your intuition by running:

str_view(c("cat", "coat", "scotland", "tic toc"), 
  pattern = "c" %R% ANY_CHAR %R% "t")

Notice that ANY_CHAR will match a space character (c t in tic toc). It will also match numbers or punctuation symbols, but ANY_CHAR will only ever match one character, which is why we get no match in coat.

Instructions 1/4
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  • 1

    Match any character followed by a t.

    • 2

      Match a t followed by any character. Notice how the final t in cat and coat don't match, that's because there is no character after the t to match to ANY_CHAR.

    • 3

      Match any two characters. Notice the first two characters are matched. Regular expressions are lazy and will take the first match they find.

    • 4

      Match a string that is exactly three characters.