Fastfile example

Fastfile

fastlane_version "1.49.0"

default_platform :ios

######################
slack_webhook = 'https://...'           #See Slack Incoming Webhook
slack_default_channel = '#channel'
default_production_scheme = 'YOUR-PRODUCTION-SCHEME'
certificates_output_path = './certificates'
profiles_output_path = './profiles'
apple_team_id = 'YOUR-TEAM-ID'
workspace_path = 'WORKSPACE-PATH'
hockey_production_token = 'TOKEN'


platform :ios do
  before_all do
     ENV["SLACK_URL"] = slack_webhook
     ENV["SCAN_SLACK_CHANNEL"] = slack_default_channel
  end
  
  desc "Responsible for building and signing the app"
  desc "Accept parameters:"
  desc "- scheme : scheme name (Optional)"
  private_lane :build_app do |options|
  	
  	# Download the updated profiles and certificates
    cert(
      development: (options[:scheme] && options[:scheme] != default_production_scheme,
      output_path: certificates_output_path,
      team_id: apple_team_id
    )

    sigh(
      output_path: profiles_output_path,
      team_id: apple_team_id
    )

  	# Build using gym
    gym(
      scheme: options[:scheme] || default_production_scheme,
      workspace: workspace_path,
      export_team_id: apple_team_id
    )
  end

  desc "Creates and uploads the ipa to TestFlight"
  lane :prerelease do

    # Asks to build the scheme
    build_app(
      scheme: default_production_scheme
    )

    hockey(
      upload_dsym_only: true,
      api_token: hockey_production_token,
      notes: '',
      notify: '0',    # do not notify
      status: '1'     # do not make available for download
    )

    # Delivers the app to testflight
    testflight(
      skip_submission: true,
      distribute_external: false
    )
  end

  after_all do |lane|
    # This block is called, only if the executed lane was successful    
    slack(
      message: "Fastlane operation completed!!",
      channel: slack_default_channel
    )
  end

  error do |lane, exception|
    slack(
      message: exception.message,
      success: false,
      channel: slack_default_channel
    )
  end
end

There are some useless constants. It's just to make people understand. It could be useful to use Appfile and Deliverfile

This looks good - you might want to check out this
https://github.com/theappbusiness/MasterFastfile

Specifically supporting multiple environments
https://github.com/theappbusiness/MasterFastfile/blob/master/setup.sh