# Regular Expressions Basics

Marchete
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## Alternations `(|)`

With `[` `]`, you have the OR operator at a character level. With alternation, you have the OR operator at the pattern level:

`(pattern1|pattern2|pattern3)` will match either `pattern1` OR `pattern2` OR `pattern3`.

Those subpatterns can be as complex as needed, and there is no limit to the number of patterns that can be separated by the `|` metacharacter.

Examples:

• Example 1: `(yes|no)` Will search for exactly `yes` OR `no`.
• Example 2: `([Yy]es|[Nn]o){2,4}` Will search for `Yes` OR `yes` OR `No` OR `no` repeated between two to four times.
• Example 3: `\b([0-9]+|[a-z]+)\b` Will search for a word made entirely of digits OR a word made entirely of lowercase letters. But it won't match mixtures of letters and digits.
• Example 4: `(([Yy]es|[Nn]o){2,4}|\b([0-9]+|[a-z]+)\b)` Combination of the two previous patterns. So it matches either the same as "Example 2" OR "Example 3".
Exercise 5 - Search Image Files

Continue to the next lesson to learn about Groups and Capturing Groups.

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