rule task_pattern => source do |task|
 # action
end

rule /^(.*)-(\d+)x(\d+)\.png$/ => [ # regexp with capture groups
 proc { "#{1ドル}.svg" } # capture variable in a source proc
 # or '1円.svg' # backreference in a source string
] do |task|
 basename, width, height = 1ドル, 2ドル, 3ドル # capture variables in an action proc
 sh "convert #{basename}.svg -resize #{width}x#{height} #{basename}-#{width}x#{height}.png"
end

rule /-(?<width>\d+)x(?<height>\d+).(?<ext>png|jpg)$/ => [ # regexp with named capture groups
 proc { "#{$`}.#{$~[:ext]}" } # matchdata in a source proc
 # or '\`.\k<ext>' # named backreference in a source string
 # or '.\k<ext>' # file extension replacement (already implemented in the current master branch)
] do |task|
 sh "convert #{task.source} -resize #{$~[:width]}x#{$~[:height]} #{task.name}" # accessing named capture groups
end

rule %r{^build/(?<basename>.*?)\.html\.(?<lang>.*?)$} => [
 'doc/\k<lang>/\k<basename>.md' # named backreference in a source string
] do
 sh "pandoc -o #{task.name} #{task.source}"
end

options.match(/^CFLAGS=(.*)$/) # extract a parameter from a multiline text
rule '.o' => '.c' do |task|
 sh "gcc #{1ドル} -c -o #{task.name} #{task.source} # 1ドル will be replaced to nil
end