00-README.md

Terminal 1:

ruby 01-build-repo.rb test.git
ruby 02b-read-refs.rb test.git

Terminal 2:

bash 02a-update-and-pack.sh test.git

Terminal 1 will say:

02b-read-refs.rb:10:in `each': Failed to open directory '/Users/spraints/github/slumlord/07363dde0a6a7ba122ba/test.git//refs/heads/': No such file or directory (Rugged::OSError)
        from 02b-read-refs.rb:10:in `each'
        from 02b-read-refs.rb:10:in `to_a'
        from 02b-read-refs.rb:10:in `block in <main>'
        from 02b-read-refs.rb:6:in `loop'
        from 02b-read-refs.rb:6:in `<main>'

01-build-repo.rb

require "rugged"

repo_path = ARGV.first or raise "Usage: ruby #{$0} TESTREPOPATH"
system "rm", "-rf", repo_path
repo = Rugged::Repository.init_at(repo_path, :bare)
blob_sha = repo.write("blah blah", :blob)
commit_shas = (1..100).map do |i|
  tree = Rugged::Tree::Builder.new(repo)
  tree << {:type => :blob, :name => "file.txt", :oid => blob_sha, :filemode => 0100644}
  sig = {:email => "me@example.com", :name => "Me", :time => Time.now}
  Rugged::Commit.create repo,
    :tree => tree.write,
    :update_ref => "refs/heads/test/#{i}",
    :message => "testing #{i}",
    :parents => [],
    :author => sig,
    :committer => sig
end
repo.close

02a-update-and-pack.sh

#!/bin/bash

set -e
set -x

export GIT_DIR=$1
test -f ${GIT_DIR}/HEAD

set +x
shas=$(git for-each-ref --format '%(objectname)' | sort -u)
echo Cycling refs/heads/master through $(echo ${shas} | wc -w) shas

heads=${GIT_DIR}/refs/heads
while true; do
  for sha in ${shas}; do
    git pack-refs --all
    test -d ${heads} && rmdir ${heads}
    git update-ref refs/heads/master ${sha}
  done
done

02b-read-refs.rb

require "rugged"

repo_path = ARGV.first or raise "Usage: ruby #$0 REPOPATH"

n = 0
loop do
  n += 1
  print "." if n % 1000 == 0
  repo = Rugged::Repository.new(repo_path)
  repo.refs("refs/heads/*").to_a
  repo.close
end

Gemfile

source "http://rubygems.org"
gem "rugged"

Gemfile.lock

GEM
  remote: http://rubygems.org/
  specs:
    rugged (0.23.2)

PLATFORMS
  ruby

DEPENDENCIES
  rugged