01 introduction_notes

1 Introduction to the Shell

Setup

• Download shell-lesson-data.zip and move the file to your Desktop.
• Unzip/extract the file. Let your instructor know if you need help with this step. You should end up with a new folder called shell-lesson-data on your Desktop.

Question:

• What is a command shell and why would I use one?

Objectives:

• Explain how the shell relates to the keyboard, the screen, the operating

system, and users’ programs.

• Explain when and why command-line interfaces should be used instead of

graphical interfaces.

Rule #1: Don’t panic!

Imagine the following task:

• copy line 1521 from all files in 200 directories into a new file
• estimate how much time this would take you with a GUI word processor
• We will see that the shell accomplishes this task in seconds

The shell is good at

• repetitive tasks
• do stuff on a remote computer (e.g. compute cluster)
• combine tools into pipelines
• automate tasks
• keep work reproducible
• Reduces risk for repetitive strain injury

The shell is not good at

• doing stuff that needs visual interaction
• visualization (although there are ways…)
• start from scratch (you gotta know the basics)

Getting started

• open your shell
• Windows: Start->git bash
• Mac: Terminal
• Linux: |CTRL-ALT-T| or |ALT-F2| “gnome-terminal”

The prompt

• “>” or “$” or combinations of these plus hostname, username, current directory, …
• do not type the prompt when entering commands

Our first shell command: ls

enter

$ ls |Enter|

• what happens?

enter

$ ks |Enter|

• what happens?

Take home

• A shell is a program whose primary purpose is to read commands and run other programs.
• This lesson uses Bash, the default shell in many implementations of Unix.
• Programs can be run in Bash by entering commands at the command-line prompt.
• The shell’s main advantages are its high action-to-keystroke ratio, its support for automating repetitive tasks, and its capacity to access networked machines.
• A significant challenge when using the shell can be knowing what commands need to be run and how to run them.