Question

If I have a string such as string = "08/01/2012"

How can I return “2012-08-01” in Ruby in one line?

e.g. take the set of digits after the last “/”, insert them at the beginning, then replace the “/”s with “-“s

Answer 1

Since you are dealing with dates, I’d go through the Date library (you have to require 'date' for some of the features) because it’s the most flexible and stable approach:

Date.strptime(string, '%m/%d/%Y').strftime('%Y-%m-%d')
#=> "2012-08-01"

As you can see both strptime (“string parse time”) and strftime (“string format time”) take format strings that exactly describe what they are doing.

If you don’t want to go through Date, you can use gsub like this:

string.gsub(%r{(\d+)/(\d+)/(\d+)}, '\3-\1-\2')
#=> "2012-08-01"