output.txt

# Unique headers
GNU "Terry Pratchett", Terry Pratchett
GNU #1
GNU Aaron Swartz
GNU Aaron Swartz, Boris Floricic, Wau Holland, Stephen Hawking
GNU Arthur William Bell III, Natalie Nguyen, Terry Pratchett, Chris Long, Howard Gobioff
GNU Douglas Adams, Terry Pratchett, Lester Haines
GNU GNU: Terry Pratchett, Jon Postel, Dennis Ritchie, Evi Nemeth, Ray Tomlinson, Evelyn Berezin
GNU Jerry Jackowski, Natalie Nguyen
GNU John Dearheart
GNU John Pinner
GNU Jon Postel, Terry Pratchett, JD Falk, Itojun, Evi Nemeth, John DuBois, Aaron Swartz, Stephen Hawking
GNU Manfred Schwingenschloegl, Johnny Cash, Douglas Adams, Terry Pratchett, Stephen Hawking
GNU Maple Syrup/Erin Pinheiro, Natalie Nguyen, Quin, Ted, Cliff, Austin, Elizabeth Waite
GNU Natalie Nguyen
GNU Natalie Nguyen, Amelia Perry, Lydia Stone
GNU Natalie Nguyen, Anthony Bourdain
GNU Natalie Nguyen, Shiina Mota
GNU Natalie Nguyen, Terry Pratchett, Chloe Sagal, Aaron Swartz, George Buzinkai
GNU Nate
GNU SPC. Christopher Alexander Patterson, Terry Pratchett
GNU Sir Terry Pratchett
GNU SophiaButler 2015
GNU Steve Symonds, Terry Pratchett
GNU Terry Pratchet
GNU Terry Pratchett
GNU Terry Pratchett Iain Banks
GNU Terry Pratchett, BiL Douglas
GNU Terry Pratchett, Dennis Hawelka, Natalie Nguyen
GNU Terry Pratchett, Douglas Adams, Stephen Hawking
GNU Terry Pratchett, Gaz Hunter, Oscar William Atha-Nicholls
GNU Terry Pratchett, Jacob Goyette
GNU Terry Pratchett, John Bernard Parker
GNU Terry Pratchett, Kevin aka Nexus
GNU Terry Pratchett, Kit Hampton, Douglas Adams, Jon Postel, Dennis Ritchie, Harlan Ellison
GNU Terry Pratchett, Leonard Nimoy, Aaron Swartz, Stephen Hawking, Natalie Nguyen, Heather Heyer
GNU Terry Pratchett, Lester Haines
GNU Terry Pratchett, Nigel Paul Taylor
GNU Terry Pratchett, Noirin Trouble Pluinceid
GNU Terry Pratchett, Piotr Molski
GNU Terry Pratchett, Raymond Glanville
GNU Terry Pratchett, Robert Anton Wilson
GNU Terry Pratchett, Robin King, Matt Jewell
GNU Terry Pratchett, Robin Williams, Aaron Swartz, Douglas Adams, William Hartnell, Patrick Troughton, Jon Pertwee, Graham Chapman, Richard Wright
GNU Terry Pratchett, Stan Lee
GNU Terry Pratchett, Stan Stent, Gareth Cook, Peter Plumridge, Patrick Morrin
GNU Terry Pratchett, Stephen Hawking
GNU Terry Pratchett, Stephen Hawking, Greg Lake, David Bowie, Greg Stafford
GNU Terry Pratchett, Stephen Hawking, Prof. Dr. Georg Riccabona
GNU Terry Pratchett, Ted Cartwright
GNU Terry Pratchett, Terry Pratchett
GNU Terry Pratchett, Walter Horriar, Achim Wegner
GNU Terry Pratchett, Wlpdh Odpslq, Paulette Wright, Orxlv Elojhu
GNU Terry Pratchett, Yoeri Lauwers, Arie Jan Stapel
GNU William Glen Harold Herrington, Stefan Karl Stefansson
GNU William Hartnell, Patrick Troughton, Jon Pertwee
GNU terry pratchett
GNU ~abraxas
GNU ~abraxas, Terry Pratchett, abraxas

script.rb

require "nokogiri"
require "net/http"
require "uri"
require "shellwords"

u = URI("https://xclacksoverhead.org/listing/the-signal")

res = Net::HTTP.start(u.host, u.port, use_ssl: (u.port == 443)) do |http|
  http.request(Net::HTTP::Get.new(u))
end

doc = Nokogiri::HTML(res.body)

unique_headers = doc.css("span.signal-gnu").map { |x| x.content }.sort.uniq

puts "# Unique headers"
puts unique_headers