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Linux Mail Server

In this guide, I will show you how to make a Linux Mail Server in fast and easy way. This guide was taken from tiq's tech-blog for recent version, Linux distro I using is Ubuntu 20.04 LTS

Certificate

Make sure you have Certificate and Key file ready to use.

You can use existing Web Server SSL certificate, since we going to use same domain, example.com.

If you plan to use mx.example.com or mail.example.com you need create another one for these.

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2. Given the file with random chars, draw a histogram of chars count.
For example for file with content

===
123456789012345678909999991234569999
===

Output should be the following:

1 ***

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# For more elaborate use cases, see the IndirectUsesTracker instead:
# https://gist.github.com/christhekeele/fc4e058ee7d117016b9b041b83c6546a

###
# A way to know, at runtime, what modules a module has used at compile time.
# In this case, you include `UsesTracker` into a module. When that module gets
# used in some other module, it registers itself with the other module.
##
defmodule UsesTracker do
  

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# For simpler use cases, see the UsesTracker instead:
# https://gist.github.com/christhekeele/e858881d0ca2053295c6e10d8692e6ea


###
# A way to know, at runtime, what modules a module has used at compile time.
# In this case, you include `IndirectUsesTracker` into a module. When that module gets
# used in some other module, it makes that module registerable under a namespace of your choosing.
# When the registerable module is used into a third module, that third module will know at runtime which
# registerables were `use`d in it at compile time, via a function titled after the namespace.

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def get_specific_version(id, version, scope) do
  datetime = Timex.parse!(version, "%FT%T.%fZ", :strftime)
             |> Timex.shift(seconds: -1)
             |> Timex.to_datetime
  q = """
  SELECT #{version_fields()} FROM #{table()}
  WHERE id = $1::integer AND sys_period @> $2::timestamptz AND scope @> $3::ltree
  UNION ALL
  SELECT #{version_fields()} from #{history_table()}
  WHERE id = $1::integer AND sys_period @> $2::timestamptz AND scope @> $3::ltree;

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Pry Cheat Sheet

• Youtube Tutorial 2013

Command Line

• pry -r ./config/app_init_file.rb - load your app into a pry session (look at the file loaded by config.ru)
• pry -r ./config/environment.rb - load your rails into a pry session

Debugger

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Flat an array without using Array#flatten method

Ruby

ary = [[1, 2, [3], []], 4]

Recursion

ary.flat_map{|element| element.kind_of?(Array) ? element.flat_map{|i| i} : element }

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/*
Copyright (c) 2015 Paul Jolly <paul@myitcv.org.uk)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

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skip_filter *_process_action_callbacks.map(&:filter), :only => [:action_goes_here]

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GET http://localhost:3000/fb/fb_code
RESPONSE
{"redirect_url":"https://www.facebook.com/dialog/oauth?client_id=893637180663238\u0026redirect_uri=http%3A%2F%2Flocalhost%3A3000%2Ffb%2Fcallback"}

----
redirect to https://www.facebook.com/dialog/oauth?client_id=893637180663238\u0026redirect_uri=http%3A%2F%2Flocalhost%3A3000%2Ffb%2Fcallback
redirect to callback_url
GET http://localhost:3000/fb/callback?code=FB_AUTH_CODE
RESPONSE
{"access_token":"FB_ACCESS_TOKEN"}