(ab)* regular expression

What does a+B mean in regex?
The + operator is typically used to indicate union ( |, "or") in academic regular expressions, not "one or more" as it typically means in non-academic settings (such as most regex implementations). So, a+b means [ab] or a|b, thus (a+b)* means any string of length 0 or more, containing any number of a s and b s in any order.
What does a+B* mean?
In normal regular expression grammar, (a+b)* means zero or more of any sequence that start with a, then have zero or more a, then a b. This discounts things like baa (it doesn't start with a ), abba, and a (there must be one exactly b after each a group), so is not correct.
Is a b a regular expression?
If a and b are regular expression, a + b is also a regular expression with language {a,b}. If a and b are regular expression, ab (concatenation of a and b) is also regular. If a is regular expression, a* (0 or more times a) is also regular. ( a ? e ? i ? o ? u ) {a, ab, abb, abbb, abbbb,….}

Overview

This article is about Regular Expressions (Regex) and explains the different symbols used in regex such as ".", "+", "*", "[ ]" etc., how to write a regular expression for an email address or phone number and also provides examples of using these symbols in regex. geeksforgeeks.org

Regex

A regular expression is a sequence of characters that define a search pattern used in string matching. It is used in every programming language and supports tools like regex testers for debugging and optimizing patterns. geeksforgeeks.org

Basic Components

The basic components include special characters, literal characters, functions/methods, character classes, escape symbol, grouping characters, comments and more. geeksforgeeks.org

Character Classes & Ranges

Character classes match any one of a set of characters while ranges match any single character within the range from first to last. Negation matches any single character not in set_of_characters. geeksforgeeks.org

Repeaters & Wildcard

The asterisk (*), plus (+) and curly braces ({}) symbols act as repeaters while the dot (.) symbol acts as wildcard taking place of any other symbol. geeksforgeeks.org

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