slack_delete.rb

require 'net/http'
require 'json'
require 'uri'

@token = ''
@username = ''

def user_id
  params = {
    token: @token
  }
  uri = URI.parse('https://slack.com/api/users.list')
  uri.query = URI.encode_www_form(params)
  response = Net::HTTP.get_response(uri)

  members = JSON.parse(response.body)['members']

  members.detect {|m| m['name'] == @username }['id']
end

def list_files
  ts_to = (Time.now - 30 * 24 * 60 * 60).to_i # 30 days ago
  params = {
    token: @token,
    ts_to: ts_to,
    count: 1000,
    user: user_id
  }
  uri = URI.parse('https://slack.com/api/files.list')
  uri.query = URI.encode_www_form(params)
  response = Net::HTTP.get_response(uri)
  JSON.parse(response.body)['files']
end

def delete_files(file_ids)
  file_ids.each do |file_id|
    params = {
      token: @token,
      file: file_id
    }
    uri = URI.parse('https://slack.com/api/files.delete')
    uri.query = URI.encode_www_form(params)
    response = Net::HTTP.get_response(uri)
    p "#{file_id}: #{JSON.parse(response.body)['ok']}"
  end
end

files = list_files
p "Deleting #{files.size} files for user #{user_id}..."
file_ids = files.map { |f| f['id'] }
delete_files(file_ids)
p 'Done!'