Perl Regular Expressions – Part 1 Justin Hummel CS 265

Basic Matching Simple Matching Matching a variable “Hello World” =~ /World/ # matches Matching a variable “Hello World” =~ /$greeting/ Matching the default variable ($_) /World/ Arbitrary delimiters “Hello World” =~ m”World”

Basic Matching Metacharacters – need to be escaped with “\” {}[]()^$.|*+?\ /$5/ # does not match “$5” /\$5/ # matches “5” Special Escape Sequences \n (new line) \t (tab) \r (carriage return) \a (bell) Anchor Metacharacters ^ (Beginning) $ (End) /^cat/ # matches “cat” and “catfish”, not “bobcat” /cat$/ # matches “cat” and “bobcat”, not “catfish”

Character Classes […] denotes a character class Will match any of the characters /[bcr]at/ # matches “bat” “cat” or “rat” “–” Character creates a range /[0-9]/ # matches 0,1,2,3,4,5,6,7,8,9 “^” Character negates the character class /[^0-9]/ # matches anything but 0,1,2,3,4,5,6,7,8,9 Special Character Classes \d (digit) \s (whitespace) \w (word character) . (anything but \n) Negated Special Character Classes Capitalized (\D,\S,\W)

Modifiers “s” – treat the entire string as a single line “.” matches “\n” “m” – treat the string as a set of multiple lines “.” does not match “\n” “^” and “$” match the start and end of the string “sm” – treat the string as a single long line, but detect multiple lines “^” and “$” match the start/end of any line in the string