shastuff.rb

require 'digest/sha1'

if ARGV.first.nil? || ['-h', '--help', '-?'].include?(ARGV.first)
  puts "Usage: #{$0} <glob>"
  exit 1
end

files = Dir[ARGV.first].sort

files.each do |file|
  next unless File.file? file
  buf = ""
  accum = ""
  
  File.open(file, 'r:binary') do |f|
    while (buf = f.read(510))
      accum << buf
      f.seek(1024*1024*2, 1)
    end
    
    puts "#{file} #{Digest::SHA1.hexdigest(accum)}"
  end
end

Thank you judofyr. I try to keep my GitHub stuff in English, so I'll do a short translation of the comment on the bottom:

Doesn't support globs, but your shell does that anyway. Same output as shasum (included in OSX)