A script to delete Time Machine backups that match a regex

delete_old_tm_backups

#!/usr/bin/env ruby

# Usage:
#   sudo delete_old_tm_backups <path to backup volume> <regex>
#
# Example:
#   sudo delete_old_tm_backups /Volumes/backup ^2019

backup_volume = ARGV.shift
delete_regex = Regexp.new(ARGV.shift)

backups = `tmutil listbackups -d #{backup_volume}`
backups_to_delete = backups
  .split("\n")
  # Extract basename from paths of the following format:
  # /Volumes/.timemachine/SOME-UUID/TIMESTAMP.backup/TIMESTAMP.backup
  .map { |dir| File.basename(dir, '.backup') }
  .filter { |dir| dir =~ delete_regex }

puts "Will delete the following backups from #{backup_volume}:"
puts "\t#{backups_to_delete.join("\n\t")}"
puts
puts "Continue? [y/N]"

confirm = gets
if confirm =~ /^y/
  backups_to_delete.each do |backup|
    system("tmutil delete -d #{backup_volume} -t #{backup}")
  end
end