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RegEx : Expressions and Parsing Examples

RegEx is a sequence of characters for a search to match a pattern. Arose in the 1950 by Stephen Kleene, an American Mathematician. Regular expressions are composed of characters, metacharacters and quantifiers.

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RegEx : Expressions and Parsing Examples

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  1. RegEx : Expressions and Parsing Examples

  2. Overview • What is RegEx • Purpose of RegEx • How it Works • Advantages • Demonstration • Q&A 2

  3. Introduction to RegEx • RegEx is a sequence of characters for a search to match a pattern. • Arose in the 1950 by Stephen Kleene, an American Mathematician. • Regular expressions are composed of characters, metacharacters and quantifiers. 3

  4. Purpose of RegEx • To match the pieces of text within a larger document. • To capture the string. • RegEx is used in PERL, Java and other programming languages. 4

  5. How it Works • Regular Expressions: Exact Matches c k s regular expression rocks. match is okay. no match 5

  6. How it Works • Regular Expressions: Multiple Matches regular expression a p p l e Scrapplefromtheapple. match 1 match 2 6

  7. Metacharacters of RegEx • . - Matches any single character. • \d - Matches a digit character. • \s - Matches any whitespace character including space, tab, form-feed, etc. • \w - Matches any word character including underscore. • \n - Matches a newline character. • ^ - The beginning of a line • $ - The end of a line 7

  8. Metacharacters of RegEx • abc - Exactly this sequence of three letters • [abc] - Any one of the letters a, b, or c • [^abc] - Any character except one of the letters a, b, or c • [a-z] - Any one character from a through z • [a-zA-Z0-9]-Any one letter or digit. 8

  9. Quantifier Quantifier specify the number of string pattern should occur in matching string. • * - Zero or more times. • + - One or more times. • ? - Zero or one time • {m,n} - Matches for atleast m times and atmost n times. 9

  10. Advantages • The regular expression syntax is declarative: The pattern "looks like" what you want to match. • Easily compatible with different programing languages. • Easier for non-programmers than code. • Less error prone than code. • Use in Compiler Construction. 10

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