You can also specify repetition within patterns.


/ab+c/ matches a string containing an a followed by one or more b's, followed by a c. 
/ab*c/ matches one a, zero or more b's, and one c.

1.	Repetition
2.	have Repetition match the minimum by adding a question mark suffix.
3.	use part of the current match later in that match allows you to look for various forms of repetition.
4.	use back references to match delimiters.
5.	A pattern that matches a string containing the text Perl or the text Python
6.	Use parentheses within patterns,just as you can in arithmetic expressions
7.	match one of a group of characters within apattern
8.	Match a time such as 12:34:56
9.	Match Perl, zero or more other chars, then Python
10.	Match Perl, a space, and Python
11.	Match Perl, zero or more spaces, and Python
12.	Match Perl, one or more spaces, and Python
13.	Match Perl, whitespace characters, then Python
14.	Match Ruby, a space, and either Perl or Python
15.	The match operator =~ can be used to match a string against a regular expression.
16.	The part of a string matched by a regular expression can be replaced
17.	Replace every occurrence of Perl and Python with Ruby

You can also specify repetition within patterns. : Regexps Repetition « Development « Ruby