Introduction to Regular Expressions

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 us to match either the characters preceding the | OR the characters after the |. The regex baboons|gorillas will match baboons in the text I love baboons, but will also match gorillas in the text I love gorillas.

Are you thinking about how to match the whole piece of text I love baboons or I love gorillas? We will get to that later on!



The interactive applet in the browser allows you to enter a regular expression and see if it matches a string of text. If a character is matched, you’ll see it highlighted in green. If there’s a checkmark next to the string, you’ve completely matched the whole piece of text!

Enter a regular expression that matches each of the strings listed below “Match these strings” and does NOT match any of the strings listed below “Don’t match these strings.”

When you’ve entered a regular expression that matches the appropriate strings, a key will appear in the browser. Add the key to the end of the URL in the code editor and run the code to unlock the next exercise!

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