Today I Learned

TIL, 2017-09-18

  • More refactoring lessons.
  • ls -R to see all files recursively.
  • touch on an existing file will change the access time.
  • Hard link, must be same physical drive.
  • Symbolic link: cp -s file file2, and ln -s file file2.
  • file myfile determine the kind of file.
  • tail is used to view the last 10 lines of a file.
  • head is used to view the first 10 lines of a file.
  • ps aux to list the currently running processes.
  • top -o cpu to list processes by CPU.
  • pkill to kill a process, xkill to kill any non-responsive window.
  • Postgres has a server.log which can only be deleted if Postgres is not running anymore.


  • yarn is Facebook’s answer to npm.
  • as the app template.
  • Create an .env file in the base directory.
  • yarn add react-router to add the react router.
  • This is sad, but declaring a function in JavaScript: aw = function() { 1 + 1 }.

Destroy All Software, Collapsing Services into Values and How and Why To Avoid Nil

class Subscription <, :type)
  attr_reader :allow_export
  alias_method :allow_export?, :allow_export

  def initialize(id, type)
    @id = id
    @type = type
    @allow_export = active? && type == 'business'

  def active?
  • Resolving nils–introduce a new domain concept (Null Object?)

This project is maintained by daryllxd