Example of adding 'Shell Script Build Phase' to Xcode project using Fastlane action and Xcodeptoj tool

insert_build_phases.rb

module Fastlane
  module Actions
    module SharedValues
      INSERT_BUILD_PHASES_CUSTOM_VALUE = :INSERT_BUILD_PHASES_CUSTOM_VALUE
    end

    class InsertBuildPhasesAction < Action
      def self.run(params)
        require 'xcodeproj'

        project_path = "MyProject.xcodeproj"
        target_name = "MyProject"
        project = Xcodeproj::Project.open(project_path)
        target = project.native_targets.select { |target| target.name == target_name }.first
        phase = create_or_update_build_phase(target, "Copy static pages")
        phase.shell_script = "rm -rf ~/Documents/www/webroot\nmkdir ~/Documents/www/webroot\ncp -a StaticPages/. ~/Documents/www/webroot"
        target.build_phases << phase
        project.save()
      end

      #####################################################
      # @!group Documentation
      #####################################################

      def self.description
        "Insert custom build phases after a new pbxproj file generated."
      end

      def self.details
        "You can use this action to do cool things..."
      end

      def self.available_options
      end

      def self.output
      end

      def self.return_value
      end

      def self.authors
        ["wowbroforce"]
      end

      def self.is_supported?(platform)
        platform == :mac
      end

      class << self
        def create_or_update_build_phase(target, phase_name, phase_class = Xcodeproj::Project::Object::PBXShellScriptBuildPhase)
          build_phases = target.build_phases.grep(phase_class)
          build_phases.find { |phase| phase.name && phase.name.end_with?(phase_name) }.tap { |p| p.name = phase_name if p } ||
            target.project.new(phase_class).tap do |phase|
              UI.message("Adding Build Phase '#{phase_name}' to project.") do
                phase.name = phase_name
                phase.show_env_vars_in_log = '0'
                # target.build_phases << phase
              end
            end
        end
      end
    end
  end
end