active_zfs_holds.rb

# Pipe `zfs history` into this script, it will output holds
# which have not yet been released.
holds = []

ARGF.each_line do |line|

  next unless line[/zfs (hold|release) (\S+) (\S+)/]
  kind = $1
  tag = $2
  snapshot = $3

  item = [tag, snapshot]

  case kind
  when "hold"
    holds << item
  when "release"
    holds.delete(item)
  end

end

puts holds.map {|x| x.join("\t") }