Regex by 131357
Download as PPTX, PDF0 likes199 views
Regular expressions are used to generate patterns of strings. A regular expression describes patterns using operators like union, concatenation, and Kleene closure. Some examples of regular expressions include: 1) Describing Canadian postal codes as /^[A-Z][0-9][A-Z] [0-9][A-Z][0-9]$/ 2) Matching strings containing the word "main" as <letter>* main <letter>* 3) Matching strings of even length as (<letter><letter>)*
![WHAT IS REGULAR EXPRESSION?
regular expressions are used to generate patterns of strings. A
regular expression is an algebraic formula whose value is a
pattern consisting of a set of strings, called the language of the
expression.
This regular expression describes Canadian postal codes
/^[A-Z][0-9][A-Z] [0-9][A-Z][0-9]$/
Any language accepted by the Finite Automata can be
represented by Regular Expression](https://image.slidesharecdn.com/regexby131357-161006212425/85/Regex-by-131357-3-320.jpg)
Regex by 131357
- 1. REGULAR EXPRESSIONS Junaid Lodhi Roll # 131357 Air University Pakistan
- 2. WHY TO STUDY REGULAR EXPRESSION?
- 3. WHAT IS REGULAR EXPRESSION? regular expressions are used to generate patterns of strings. A regular expression is an algebraic formula whose value is a pattern consisting of a set of strings, called the language of the expression. This regular expression describes Canadian postal codes /^[A-Z][0-9][A-Z] [0-9][A-Z][0-9]$/ Any language accepted by the Finite Automata can be represented by Regular Expression
- 4. OPERATORS USED IN REGULAR EXPRESSIONS I. Union: If R1 and R2 are regular expressions, then R1 | R2 (also written as R1 U R2 or R1 + R2) is also a regular expression.L(R1|R2) = L(R1) U L(R2). II. Concatenation: If R1 and R2 are regular expressions, then R1R2 (also written as R1.R2) is also a regular expression.L(R1R2) = L(R1) concatenated with L(R2). III. Kleene closure: If R1 is a regular expression, then R1* (the Kleene closure of R1) is also a regular expression.L(R1*) = epsilon U L(R1) U L(R1R1) U L(R1R1R1) U ... NOTE: Closure has the highest precedence, followed by concatenation,
- 5. EXAMPLES OF REGULAR EXPRESSION The set of strings over {A..Z,a..z} that contain the word "main". Let <letter> = A | B | ... | Z | a | b | ... | z <letter>* main <letter>*
- 6. EXAMPLES CONTINUED Set of EVEN Length String Regular expression can be made as
- 7. EXAMPLES CONTINUED Set of ODD Length String Regular expression can be made as
- 8. EXAMPLE CONTINUED Set of Strings Divisible by 3 Regular expression can be made as
- 9. PRACTICE QUESTION Congruent to 2 mod 3 What can be the Regular Expression?