1. Searching using regular expressions

2. A regular expression is also a ‘special text string’ for describing a search pattern. Regular expressions define patterns of characters that are applied to a block of text for the purpose of locating that text. ‘Jack and Jill went up the hill to fetch a pale of water’ Regular expression: ‘e’ (single literal character) (The ‘regex’ once told will go onto find further occurrences of ‘e’) 1 1 2 2 5 5 3 3 4 4

3. Searching using regular expressions The special text string might take on a different form. ‘The bed had been badly put together, but I bedded down for the night all the same’ Regular expression: ‘{b (a | e) d}’ (register bad & bed) (This kind of a function could be used to search web pages and word documents for important strings) 1 1 2 2 3 3

4. Searching using regular expressions Simple searching Any single character matches itself, unless it is a metacharacter with a special meaning. Characters that normally function as metacharacters are preceded by a backslash when they need to be Interpreted literally. Example: ‘bed’ matches substring ‘bed’ in ‘bedded

5. Searching using regular expressions Dot matches almost any character The dot matches a single character without caring what that character is, unless it is the newline character. Example: Therefore,.an matches strings: -can -flan -ban -ran

6. Searching using regular expressions Predefined shorthand classes In predefined classes, the metacharacter ‘\’ functions to escape the normal meaning of the following characters (eg \d means treat ‘d’ as a metacharacter, not as a literal character. Example: The x \ d matches “x0”, “x1”, “x2”, “x3”, “x4”, “x5” (‘d’ matches a single numeric character)

7. Searching using regular expressions Predefined shorthand classes Other examples include: Example: The be \ w matches “bed”, “bee”, “beg”, “ben”, “bet” (\w matches a single alphanumeric character (a – z, A – Z, 0 - 9) and the underscore character _. The be \ W matches “be!”, “be”, “be£”, “be$”, “be%” (\W matches a single non-alphanumeric character. \W is short for [ \w]

8. Searching using regular expressions Predefined shorthand classes Other examples include: Example: /D matches a single non numeric character and is equivalent to [ \d] /s matches a single space. /S matches any single non-space character and is the equivalent of [ \s]