Mention the user responsible for a build on Circle

config.yml

commands:  
  notify-slack-deploy-complete:
    steps:
      - slack/status:
          mentions: "$(.circleci/utility/github_username_to_slack_uid $CIRCLE_USERNAME)"

github_username_to_slack_uid

#!/usr/bin/env ruby

class GithubUsernameToSlackUid
  class << self
    def call(github_handle)
      new(github_handle).call
    end
  end

  PREFIX = "GITHUB_TO_SLACK_"
  private_constant :PREFIX

  def initialize(github_handle)
    @github_handle = github_handle
  end

  def call
    print slack_id
  end

  private

  attr_reader :github_handle

  def environment_settings
    @environment_settings ||= `printenv`.split("\n")
  end

  def matching_setting
    environment_settings.
      find { |el| (/#{PREFIX}#{github_handle}/i).match(el) }
  end

  def slack_id
    matching_setting.split("=").last
  end
end

GithubUsernameToSlackUid.call(ARGV.first)

This assumes you have environment variables defined on your system of the following form.

Variable:

"#{PREFIX}#{GITHUB_USERNAME}"

Value: Slack UID

We used a context that defines a variable like that for each member of our team, and mixed it into any job that was touching Slack.

This requires Ruby available on your build container. If that is a problem, it shouldn't be hard to reimplement in the language of your choice. You really just want something that will return a Slack UID.