What is the shell?

1. CLI vs GUI
   • command line interface
   • graphical user interface
2. the command shell is just a program providing a REPL interface with the computer operating system
3. REPL: read-evaluate-print loop
   • similar to MATLAB console, or interactive perl/python environments
   • read the input from the command line (the stuff you typed in)
   • evaluate the input, reading files and calling other programs as necessary
   • print the output back to the screen
   • loop back to the input prompt, ready for new input
4. shells:
   • common: bash (Bourne Again SHell), zsh, dash
   • less common now: tcsh, csh, ksh
5. the prompt: customizable and often different on different systems, but usually represented as a $
6. some considerations, before we move on:
   • case-sensitive
   • avoid whitespace in file names
   • other bad characters in file/folder names: all punctuation except . - _
   • . is a dot
   • / is a forward-slash, \ is a back-slash
   • # is a pound, hash, or octothorpe
   • $ is a dollar sign
   • * is a star, or an asterisk
   • ^ is a caret
   • () are parentheses or parens
   • [] are square brackets
   • {} are braces or curly brackets
   • _ is an underscore
   • - is a hyphen, dash, or minus sign
   • ~ is a tilde
   • ` is a back tick
   • ' is a single quote
   • " is a double quote
   • sometimes I will represent generic placeholders by placing them between a less-than sign and a greater-than sign, <like so>. The angle brackets aren't needed in the actual commands.
   • be careful with pasting from Word, Pages, some email clients, and some web browsers since the straight single and double quotes can be auto-corrected to curly single and double quotes