Question

From Guardfile examples:

watch(%r{^app/(.+)\.rb})    { |m| "spec/#{m[1]}_spec.rb" }
watch(%r{^lib/(.+)\.rb})    { |m| "spec/lib/#{m[1]}_spec.rb" }

What do the values of m represent? It seems to be an array of length 2, storing the complete path and relative path…

How is m generated? Is it coming from Guard or Ruby?

Answer 1

m[1] would be the first capture group in the regex match. And from the regex, that is the name of the file ( without the extension.)

This is actually explained in the README:

guard :rspec do
  watch(%r{^lib/(.+)\.rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
end

In this example the regular expression capture group (.+) is used to transform a file change in the lib folder to its test case in the spec folder. Regular expression watch patterns are matched with Regexp#match.