Understanding Regular Expressions in Programming Languages

1. The College of Saint Rose CIS 433 – Programming Languages David Goldschmidt, Ph.D. Regular expressions{week 06} from Concepts of Programming Languages, 9th edition by Robert W. Sebesta, Addison-Wesley, 2010, ISBN 0-13-607347-6

2. Regular expressions (i) • A regular expression is an expression ina “mini language” designed specificallyfor textual pattern matching • Support for regular expressions are availablein many languages, including Java, JavaScript,C, C++, PHP, etc.

3. Regular expressions (ii) • A pattern contains numerous character groupings and is specified as a string • Patterns to match a phone number include: • [0-9][0-9][0-9]−[0-9][0-9][0-9]−[0-9][0-9][0-9][0-9] • [0-9]{3}−[0-9]{3}−[0-9]{4} • \d\d\d−\d\d\d−\d\d\d\d • \d{3}−\d{3}−\d{4} • (\d\d\d) \d\d\d−\d\d\d\d

4. Regular expressions (iii)

5. Regular expressions (iv)

6. Regular expressions in Java (i) • The String class in Java provides a pattern matching method called matches(): • Unlike other languages, Java requires the pattern to match the entire string String s = "Pattern matching in Java!"; String p = "\\w+\\s\\w+\\s\\w{2}\\s\\w+!"; if ( s.matches( p ) ) { System.out.println( "MATCH!" ); }

7. Regular expressions in Java (ii) • Additional pattern-matching methods: • Use the replaceFirst() and replaceAll() methods to replace a pattern with a string: String s = "<title>Cool Web Site</title>"; String p = "</?\w+>"; String result = s.replaceAll( p, "" );