command_1_mac.md

Command line 1 for Mac

---

General

• References: Much of the content of these sessions is summarized at our Command line quick reference page.
• Credit: Our materials are based on the Software Carpentry Unix Shell course
• Etherpad: We’ll create an Etherpad where participants who wish to do so can take notes collaboratively. For a quick overview of Etherpad functionality see http://write.flossmanuals.net/etherpad/introduction/.
• Something to play with: Follow the instructions at http://swcarpentry.github.io/shell-novice/setup.html to copy some practice files.

Why and how do we use the shell?

• The shell is a program that runs other programs.
• We use the shell to interact with the computer on the command line (CLI ~ GUI).
• The Unix philosophy is that you can pipe (chain) together small commands, each of which does one thing well, to do something complex. You can’t do this in a GUI.
• MacOS 10.14 and earlier default: bash = ‘Bourne again shell’ (the original Bourne shell is sh, which you will still run into sometimes!)
• MacOS 10.15 and later default: zsh = 'Z shell', an "extended Bourne shell". Works almost but not entirely like bash.
• Not sure which shell you're using? Type echo $SHELL at the command prompt.
• Learn the shell on a need-to-know basis.

Launching the shell

• The Terminal.app that you will find in the Applications → Utilities folder. (Many Mac users prefer the free third-party https://www.iterm2.com/, but in this class we will use Terminal.)
• IF YOU ARE USING ZSH: Run the command echo setopt interactivecomments >> $HOME/.zprofile now. You'll thank me later.

Looking around

Change to your home directory, look at it with pwd.

• cd ~
• cd ..
• cd -
• cd; cd Desktop
• cd data-shell/data/s... (tab completion)
• cd /Users/djb/Desktop/data-shell/data (absolute path)

Change to Desktop/data-shell

• ls -F
• ls -j (unsuppored)
• man ls
• ls data

Dragging a file from your filesystem Finder/Explorer window to the terminal

ls switches

• ls -a: include hidden files (filenames starting with .)
• ls -l: show enhanced file information, including date and time stamps, owner and group, permissions
• ls -t: list in timestamp order
• ls -G: colored output
• ls -lh: human readable file size
• ls -F: decorate filenames according to filetype
• ls -d: don’t recurse into directories
• ls -1: single-column
• ls -d */: list only directories

History and completion

• Command and filename completion with the Tab key
• Command history with the arrow keys

Summary

• The file system is responsible for managing information on the disk.
• Information is stored in files, which are stored in directories (folders).
• Directories can also store other directories, which forms a directory tree.
• cd path changes the current working directory.
• ls path prints a listing of a specific file or directory; ls on its own lists the current working directory.
• pwd prints the user’s current working directory.
• whoami shows the user’s current identity.
• / on its own is the root directory of the whole file system.
• A relative path specifies a location starting from the current location.
• An absolute path specifies a location from the root of the file system.
• Directory names in a path are separated with ‘/’ on Unix (including Mac OS)
• .. means ‘the parent directory = the directory above the current one’
• . on its own means ‘the current directory’. Why would we need this?
• Most filenames have conventional extensions: .txt, .xml, etc.
• Most commands take options (flags) which begin with a -.