1. Perl Regular Expressions – Part 1
Justin Hummel
CS 265

2. 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”

3. 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”

4. 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)

5. 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