slack-poster - upload your files to #general channel.

slack-poster.rb

#!/usr/bin/env ruby

# See https://api.slack.com/methods/files.upload
# See https://qiita.com/ykhirao/items/3b19ee6a1458cfb4ba21
# Set your env var: SLACK_POSTER_TOKEN.
# $ grep SLACK_POSTER_TOKEN ~/.bash_profile
# export SLACK_POSTER_TOKEN=xxxx-9999999999-999999999999-ZZZZZZZZZZZZZZZZZZZZZZZZ

require 'json'
require 'slack/poster'

def main
  if ARGV.length == 0
    puts "Usage: slack-poster filename.png ... "
    puts "Post filename.png ... to your slack channel."
    abort
  end

  ARGV.each do |filename|
    json = `curl -F file=@#{filename} -F channels=#general -F token=#{ENV['SLACK_POSTER_TOKEN']} https://slack.com/api/files.upload`
    result = JSON.parse(json)
    if !result["ok"]
      abort("ERROR")
    else
      puts result["file"]["permalink"]
    end
  end
end

main

cf. https://api.slack.com/methods/files.upload
cf. https://qiita.com/ykhirao/items/3b19ee6a1458cfb4ba21