twit_anime_icon.rb

#!/usr/bin/env ruby

# twit_anime_icon.rb
# convert an animated gif file to an uploadable format for Twitter.

infile = ARGV[0] || ""
outfile = ARGV[1] || "output.gif"

if infile.empty?
  puts "usage: #{$0} input.gif [output.gif]"
  exit 1
elsif !File.file?(infile)
  puts "#{infile}: file not found"
  exit 1
elsif File.exist?(outfile)
  puts "#{outfile}: file exists"
  exit 1
end

size = File.size(infile)
open(infile, "rb") {|fi|
  data = fi.read(size - 1)

  if fi.read != 0x3b.chr
    puts "#{infile}: invalid input file"
    exit 1
  end

  open(outfile, "wb") {|fo|
    fo.write data
    fo.write 0x3c.chr
    fo.write 0x2c.chr
  }
  puts "success"
}