gem-naming.rb

hyphens     = 0
underscores = 0
nothing     = 0
total       = 0

# gem list --remote > remote.txt
File.read("remote.txt").each do |gem_details|
  name, version = gem_details.split
  
  if name.include?("_") # also consumes ones with *both* _ and - as per github username-gem_name style gems
    underscores += 1
  elsif name.include?("-")
    hyphens += 1    
  else
    nothing += 1
  end
  
  total += 1
end

def percent(total, num)
  pc = (num.to_f / total.to_f) * 100.0
  "#{pc.ceil}%"
end

puts "out of #{total} gems, #{percent(total, hyphens)} (#{hyphens}) use hyphens, #{percent(total, underscores)} (#{underscores}) use underscores and the other #{percent(total, nothing)} (#{nothing}) are just one word"

output

At the time of writing:

out of 18068 gems, 46% (8186) use hyphens, 24% (4293) use underscores and the other 31% (5589) are just one word