CGS – 4854 Summer 2012 Web Site Construction and Management Instructor: Francisco R. Ortega Chapter 5 Regular Expressions

Today’s Lecture Chapter 5 Regular Expressions Talk about tutorial 4 and homework 4 Help with homework #4

Mid-Term Mid-Term June 21 st. – Chapters 1,2,3 and 4. Possible review for mid-term – June 14 (after quiz 4) or June 19 Extra Credit for Mid-Term – Extra credit question may be Java related or Regular Expressions (if covered before the exam) You are allowed to bring one letter size paper to the exam

ASCII Table (Part 1)

Regular Expressions Match strings of text (wiki) Sequence of regular expressions is known as a pattern Regular expressions contain – Wildcards – Special characters – Escape sequences

Regular Expressions 101 Characters match themselves except: [\^$.|?*+() \ suppresses the meaning of special characters [] starts a character class. We match one from the class. - specifies a range of characters ^ negates a character class. matches any single character except line break | matches either the left, or the right (or)

Character Classes [xyz] : will match x or y or z [a-z] : will match lowercase letters [a-zA-Z] : will match all letters [a-Z] :will not match any letters (why?) [A-z] : will match all letters but additional symbols. Why? [^abc] : Any character except for a,b or c.

Predefined classes Character classMeaning.Any character except line termination \dA digit: [0-9] \DA non digit [^0-9] \sA whitespace character \SA non-whitespace character \wA word character [a-zA-Z_0-9] \WA non word character

Escape Sequence \. : would match a period [.] : would match a period \ does not lose special meaning inside square brackets [\d]

Alternation yes|no yes|no|maybe – It will match either yes,no or maybae. But only one of them.

Grouping and Capturing (pattern) – Capturing pattern. Can retrieve values from \1 thru \9 – Example Text: abyes3 [a-z] ([a-z]) (yes|no) \d – \1 is equal to b – \2 is equal to yes (?:pattern) – Only used for grouping

Ignoring case (?i)yes|no – [yY] [eE] [sS] | [Nn] [Oo]

Repetition Repetition SymbolMeaning *Matches zero or more occurrences of the preceding pattern ?Matches zero or one occurrences of the preceding pattern +Matches one or more occurrences of the preceding pattern {m,n}Range of times that the pattern can repeat. ? Same as {0,1} {m}Range of exactly how many times that will match the pattern. {m,}Range of at least times that will match the pattern. + same as {1,}

Regex in java You will need to use two backslashes – Regex: \d – Java regex: “\\d”