Introduction to BDD with Cucumber | Engine Yard Blog

Introduction to BDD with Cucumber | Engine Yard Blog (via Instapaper)

As you can see from above, the basic structure of a step definition is the keyword (i.e. Given , When , or Then ) followed by a regular expression and a block of Ruby code. The regular expression is used to identify the desired step implementation. The step text in scenarios is matched against the regular expressions of appropriate (i.e. given , when , or then ) step implementations to find the one to use. When a match is found, the substrings matching any groups in the regular expression are used as arguments to the block which is then evaluated. The result of that evaluation is discarded. Note that these arguments are always strings. If you need them converted to other types, it’s up to you to do that conversion in the block. These groups and parameters have knowledge of position (i.e.. group 1 is used as the first parameter, group 2 as the second, and so on).

Full article: http://www.engineyard.com/blog/2009/cucumber-introduction/