Linux / Command line intro

• Almost everything here should work for both Linux and MacOS.
• Python, Ruby, and many other languages can run in REPL mode
  • _R_ead _E_xecute _P_rint _L_oop.
  • demonstrate Python in REPL mode (e.g., use it as a calculator)
• Terminal vs. shell
  • Terminal is the program that opens a window, runs a program, and allows text I/O.
    • e.g., Terminal.app
    • Launch XQuartz then run xterm ./hello_world
    • xterm provides a window in which to run hello_world
  • The “shell” is a specific program that runs in the terminal that allows you to tell the operating system what to do.
    • Common shells include sh, bash, csh, tcsh, zsh.
    • They are more alike than different.
    • I will use bash for this course.
• The shell is a lot like a programming language.
  • But, we’ll get to that later.
  • For now, just think of it as something you use to issue commands.
• There are two types of commands:
  • Directions to the shell specifically
    • (e.g., cd, echo, source, type)
    • run type -a cmd to check whether cmd is built-in
  • programs to execute.
  • If you type something, you either (a) run the built-in command, or run a program with that name.
  • python runs the program named python.

File system

• Groups of files are called directories
• Directories and folders are effectively the same thing.
• Files are organized in a hierarchical tree.
  • Just like folders are nested withing folders, directories are nested within directories.
• Open inClass 6. Browse file system graphically.
• In a terminal, we do this with text commands
  • ls: List the files
  • cd: _c_hange _d_irectory
  • ls -l: long: Show file properties.
  • ls -a: show all files – including hidden files.
• Hidden files begin with .
  • Create hidden file and show that it only appears when using -a
• Two special hidden files:
  • .: current directory
  • ..: parent directory
• cd .. to move up.
• pwd: print working directory
• cat: displays the contents of a file
• head: displays the first few lines
• A path is a sequence of directories that identifies a file.
• Two types
  • Absolute:
    • a “full” name
    • path shows how to get to the file from the root.
  • Relative
    • A “local” name
    • path shows how to get to the file from the current working directory.
• When you use cat or head (or many other programs) you supply a path of some kind.
  • Give examples.
  • current directory (with and without .)
  • parent directory
  • sibling directory
  • absolute path
• Which type of path you use depends on the context
  • Just as whether you use GPS coordinates, or “how to get there” directions depends on the context.
• Key idea: You can reference the desired file from anywhere
  • You only need to change directories if you want to.
• show how wildcards/globs work

Running Python as a program

• Although Jupyter notebooks are becoming increasingly popular, many python programs are intended to “stand alone” like the other programs on your computer.
• Put the desired code in a file with the .py extension.
• run python _path_to_file
• Give an example.

Misc

• If extra time,
  • show wildcards/glob
  • show mac Terminal and EOS