Rename files en masse on Amazon S3

s3-rename-mass.rb

require "aws-sdk"

s3 = Aws::S3::Client.new(region: ENV.fetch("region", "us-west-2"))

objects = []
start_after = nil

loop do
  resp = s3.list_objects_v2(
    bucket: ENV.fetch("bucket"),
    max_keys: ENV.fetch("max_keys", 1000).to_i,
    start_after: start_after,
    prefix: ENV["prefix"]
  )

  objects += resp.contents
  start_after = resp.contents.last.key
  
  break if resp.is_truncated != true
end

objects.each do |object|
  key_parts = object.key.split("/")

  if key_parts.size > 1
    s3.copy_object(
      bucket: ENV.fetch("bucket"),
      copy_source: ENV.fetch("bucket") + "/" + object.key,
      key: key_parts.join("-")
    )
  end
end