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Optional Quantifiers in Regular Expressions

In Regular expressions, optional quantifiers are denoted by a question mark ?. It indicates that a character can appear either 0 or 1 time. For example, the regular expression humou?r will match the text humour as well as the text humor.

Introduction to Regular Expressions
Lesson 1 of 1
  1. 1
    When registering an account for a new social media app or completing an order for a gift online, nearly every piece of information you enter into a web form is validated. Did you enter a properly f…
  2. 2
    The simplest text we can match with regular expressions are literals. This is where our regular expression contains the exact text that we want to match. The regex a, for example, will match …
  3. 3
    Do you love baboons and gorillas? You can find either of them with the same regular expression using alternation! Alternation, performed in regular expressions with the pipe symbol, |, allows…
  4. 4
    Spelling tests may seem like a distant memory from grade school, but we ultimately take them every day while typing. It’s easy to make mistakes on commonly misspelled words like consensus, and on t…
  5. 5
    Sometimes we don’t care exactly WHAT characters are in a text, just that there are SOME characters. Enter the wildcard .! Wildcards will match any single character (letter, number, symbol or …
  6. 6
    Character sets are great, but their true power isn’t realized without ranges. Ranges allow us to specify a range of characters in which we can make a match without having to type out each ind…
  7. 7
    While character ranges are extremely useful, they can be cumbersome to write out every single time you want to match common ranges such as those that designate alphabetical characters or digits. To…
  8. 8
    Remember when we were in love with baboons and gorillas a few exercises ago? We were able to match either baboons or gorillas using the regex baboons|gorillas, taking advantage of the | symbol. Bu…
  9. 9
    Here’s where things start to get really interesting. So far we have only matched text on a character by character basis. But instead of writing the regex \w\w\w\w\w\w\s\w\w\w\w\w\w, which would mat…
  10. 10
    You are working on a research project that summarizes the findings of primate behavioral scientists from around the world. Of particular interest to you are the scientists’ observations of humor in…
  11. 11
    In 1951, mathematician Stephen Cole Kleene developed a system to match patterns in written language with mathematical notation. This notation is now known as regular expressions! In his honor, the…
  12. 12
    When writing regular expressions, it’s useful to make the expression as specific as possible in order to ensure that we do not match unintended text. To aid in this mission of specificity, we can u…
  13. 13
    Do you feel those regular expression superpowers coursing through your body? Do you just want to scream ah+ really loud? Awesome! You are now ready to take these skills and use them out in the wild…

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