git-id

#!/usr/bin/env ruby

# git-id: calculates the git ID (sha-1) with the specified object type

require 'optparse'
require 'openssl'

type = 'blob' # as default

opt = OptionParser.new
opt.version = "0.1.0"
opt.banner =  "Usage: #{opt.program_name} [options] FILE [MORE_FILES...]"
opt.on('-h', '--help', 'Shows help message') do
  puts opt
  exit
end
opt.on('-v', '--version', 'Shows version') do
  puts opt.ver
  exit
end
opt.on('-t TYPE', '--type TYPE', 'object type: blob(default), tree, commit, or tag') do |t|
  if ['blob', 'tree', 'commit', 'tag'].member? t
    type = t
  else
    STDERR.puts "Invalid type: #{t} (must be one of blob, tree, commit, or tag)"
    exit
  end
end
opt.parse! ARGV

if ARGV.size == 0
  STDERR.puts "FILE is not spefified"
  puts
  puts opt
  exit
end

for file in ARGV
  if File.exist? file
    bytes = File.binread file
    digest = OpenSSL::Digest::SHA1::hexdigest "#{type} #{bytes.size}\0#{bytes}"
    puts "#{digest} [#{type}] #{file}"
  else
    STDERR.puts "Error: file does not exist: #{file}"
  end
end