func extension(filename) {
filename.match(/(\.[a-z0-9]+)\z/i).to_s
}
var files = [
'http://example.com/download.tar.gz',
'CharacterModel.3DS',
'.desktop',
'document',
'document.txt_backup',
'/etc/pam.d/login',
]
files.each {|f|
printf("%-36s -> %-11s\n", f.dump, extension(f).dump)
}