terminal.txt

Tutorial style walkthrough:
  https://duckduckgo.com/?q=cheetsheet+of+unix+commands

iTerm
  The terminal application that we run
  You also have one called "Terminal"

Directories (folders... but use the word "directory")
  ~                  The home directory (where your Desktop and Downloads are)
  .                  The current directory (the output of pwd)
  ..                 The parent directory (you had to go through it to get to current location)
  /                  The root directory, highest directory in your computer.
  ~/Downloads        Within the home directory, a directory named Downloads

Other notes:
  Many programs output nothing if they succeed (e.g. cp)
  Configuration for bash (e.g. shell colours) is in ~/.bash_profile (edit this with atom)

Unix program examples
  bash                     The "shell", the default program that lets us interact with the computer (when we are typing commands, we are in the shell)
  pwd                      "Print Working Directory", our current location in file system
  ls                       List files in our directory
  ls ~                     List files in other/dir
  ls -l                    List files in long-format
  l                        List files with all the custom options we set up for you
  touch notes              Makes an empty file called "notes"
  rm notes                 Remove the file called "notes"
  which ruby               Tell me where the ruby program is located
  cp .pryrc ~/.pryrc       Copy the file "./.pryrc" in the current directory to "~/.pryrc" (ie copy from current dir to home dir)
  cp .pryrc ~/.pryrc       Move the file "./.pryrc" in the current directory to "~/.pryrc"
  mv program program.rb    This move renames the file
  mkdir deleteme           Makes a directory named "deleteme"
  cd ~/deleteme            Change Directories to "deleteme" within the home directory
  echo a b c               Print the arguments (will print "a b c")
  env                      List out all your environment variables
  cat ~/.bash_profile      Prints the contents of your bash profile

Other programs
  ruby my_program.rb       Run the Ruby interpreter against the file "my_program.rb" in the current directory
  gem install pry          Install the pry gem (program and code that we can now use)
  brew install git         Use the homebrew program to install the git program
  rvm use 2.1.2            Tell rvm that I want my Ruby to be 2.1.2, it will change the environment to make this true (assuming its installed)
  git log                  Show every time I committed my code (think of this like every place the program was saved) -- this would need to be run inside of a git repository
  pry                      Launch pry, a repl that's better than irb
  atom .                   Open my current directory in the Atom text editor

Bash script (programming language you can type in the shell -- the same place you enter the programs to run)
  a=1                      Set the variable a to have the value 1 (`a = 1` would be "invoke the program a, giving it the arguments "=" and "1")
  export a=1               Set the environment variable a to have the value 1 -- Environment variables are available to programs you run
  alias l="ls -lFGgohq"    When I type "l", the shell translates that to "ls -lFGgohq", so I don't have to remember those flags
  source ~/.bash_profile   Execute the code in my home directory's bash_profile
  type gs                  Tell me what gs is (like which, but will also tell you about aliases and functions)

Playing with inputs and outputs
  Every program has one input, called the "standard input", often abbreviated as "stdin"
  By default, this is connected to your keyboard. For example:
  $ ruby -e 'puts "You said: #{gets.inspect}!"'
  This program will wait for you to enter a value on the keyboard, then print it out.
  You can override stdin with "<", to instead pull from a file.
  $ ruby -e 'puts "You said: #{gets.inspect}!"' < ~/.bash_profile

  Every program has two outputs, the "standard output" (stdout) and the "standard error" (stderr)
  By default, both of these are set to display on your screen
  You can override stdout with ">", and stderr with "2>" to instead write to a flie
  $ ruby -e '$stdout.puts("hello"); $stder.puts("world")'

  $ ruby -e '$stdout.puts("hello"); $stder.puts("world")' > f
  $ cat f

  $ ruby -e '$stdout.puts("hello"); $stder.puts("world")' 2> f
  $ cat f

  $ ruby -e '$stdout.puts("hello"); $stder.puts("world")' > f1  2> f2
  $ cat f1
  $ cat f2

  $ rm f f1 f2

  You can connect one program's output to another program's input with a "pipe"
  $ echo world
  $ echo world | ruby -e 'puts "hello, #{gets}"'