What are regular expression patterns

Regular Expressions provide a group of patterns in order to match characters. Basically they are categorized into 3 types,

1. Brackets: These are used to find a range of characters. For example, below are some use cases,
2. [abc]: Used to find any of the characters between the brackets(a,b,c)
3. [0-9]: Used to find any of the digits between the brackets
4. (a|b): Used to find any of the alternatives separated with |
5. Metacharacters: These are characters with a special meaning. For example, below are some use cases,
6. \d: Used to find a digit
7. \s: Used to find a whitespace character
8. \b: Used to find a match at the beginning or ending of a word
9. Quantifiers: These are useful to define quantities. For example, below are some use cases,
10. n+: Used to find matches for any string that contains at least one n
11. n*: Used to find matches for any string that contains zero or more occurrences of n
12. n?: Used to find matches for any string that contains zero or one occurrences of n