1. is
1.1. A special sequence of characters that define a search pattern for matching, mainly, with strings
1.2. A sequence of characters that define a search pattern
2. tools
2.1. regex101.com
2.2. regexper.com
3. has
3.1. Basic Syntax Summary
3.2. Terminology
3.2.1. REGULAR EXPRESSION is the pattern itself
3.2.2. Regular Expressions may be surrounded by DELIMITERS
3.2.3. How the pattern is interpreted is influenced by MODIFIERS
3.3. types of characters
3.3.1. Meta Characters
3.3.1.1. are
3.3.1.1.1. special characters used within regular expressions
3.3.1.2. Charater Classes
3.3.1.2.1. Can list one or more characters. It says: any of these characters can be seen as a match.
3.3.1.2.2. [abcdef] [a-f] [a-f_%0-9]
3.3.1.2.3. ^ is used to invert. It says: anything not in this class
3.3.1.2.4. To match a - (dash), use it the first beginning or in the end
3.3.1.3. Wildcard
3.3.1.3.1. . (dot)
3.3.1.3.2. It looses its wildcard function when inside a class
3.3.1.4. Quantifiers
3.3.1.4.1. are
3.3.1.4.2. single character quantifiers
3.3.1.5. Alternations
3.3.1.5.1. | - pipe
3.3.1.6. Grouping
3.3.1.6.1. is
3.3.1.6.2. ( )
3.3.1.7. Anchors & Boundaries
3.3.1.7.1. Anchors are a way to assert where we expect boundaries in the string we are examining