RaspberryPi shell programming - getting to know Busybox and its Shell

Duration: 3 Days

Course Background

The goals of this course are to get build on your basic Linux skills and to introduce you to the world of Shell programming ( or shell scripting as it is often referred to). The course will make use of not only Linux running on the Raspberry Pi, but, also regular Linux running either standalone or on VMWare or VirtualBoxrunning on a Window platform. As well as covering the simpler (Ash - A Shell) that is part of Busybox we will also cover the basics of Bash shell programming (Bash being the most common shell found on larger Linux installations). Here, again, we are conforming to our policy of getting more people confident in using Linux. We feel that this is especially important for those in the teaching profession as Linux is, sadly, very under-represented in most schools. There will also be time on the course to ask questions that might have arisen from materials presented in the introductory course.

Linux in particular, and Unix in general has very much of a "Lego" philosophy behind it. The idea is to provide a lot of well designed small tools and components that do one particular job and do it well, and then to provide a mechanism for combining these components to achieve more complex goals. It is the purpose of the shell programming language to provide the means for combining these components together. Think of a shell program as a kind of glue language. When developing shell scripts use will be made of various Linux command line tools and utilities (and there will be a chance to refresh your understanding of these commands and utilities).

Each attendee will be given a RaspberryPi to take with them after the course, and, much more importantly the knowledge and confidence to apply their new found shell programming skills not only to Linux running on a PC or a RasbperryPi, but to other Linux devices also.

Course Benefits

Probably the next daunting task after installing Linux, finding your way around it, and getting to know how to use some of the command and utilities is to learn how to read and write shell scripts.

You'll learn how to write shell scripts to create and process batches of files. You'll also learn something of rapid prototyping - because this is an area that shell programming is good for. You'll gain insights into the Unix philosophy of automating work wherever possible e.g. automating uploading of content to a web server, automating the configuration and installation of applications.

You will also be introduced to the philosophy of mini-langages as exemplified e.g. by sed and awk. Amongst other skills you will learn some quite powerful and useful sed and awk one liners. We will also tell you about Cygwin, which will enable to apply some of your knowledge of Linux command line tools and utilities and shell programming to the Windows environment.

Course Prerequisites and Target Audience

Attendees should have a basic understanding of Linux, e.g. as might be acquired by attending the Introduction to the RaspberryPi course. You are expected to have a basic knowledge of how to use Linux, both from the desktop and from the command line. You are not expected to be programmers, though a little prior exposure to e.g. Javascript or VBA would not go amiss. As always, a positive attitude to open source software would be most helpful, as would an enthusiasm for exploring and playing around with new technologies.

Course Outline

Introduction

Overview of command line tools and utilities
Introduction to Cygwin - bringing Linux tools and utilities to Microsoft Windows
Accessing and using manual pages

Basic utilities

Simple filters: cat, wc, head, tail, tr, uniq...
Sorting and searching tools: find, sort, grep, wildcards
System reporting tools: ls, du, df, ps, netstat, uname, date ...
Stream editing with sed
Building solutions by combining tools

Searching and matching text with regular expressions

Regular Expression syntax
Examples using grep
Other contexts for using regular expressions
Substitutions using tagged regular expressions in sed and vi

Creating Shell Scripts

Passing arguments to a script
Built-in variables and environment variables
I/O with echo and read
Redirecting input and output
Arithmetic and string operations

Flow control in the shell

Conditional execution with if ... else
Testing exit status of a command
Testing file properties
Looping with for, while and until
Multiway branching using case
Busybox Ash and Bash compared

Advanced shell features

Defining functions and aliases
Command substitution
Structuring data with arrays
Command sequencing and grouping

Using sed to process documents

How a stream editor works
sed as an example mini-language
Using sed scripts to modify documents - word substitution, rearrangment of text
Using sed to modify tags in HTML documents or XML documents

Using awk to process structured input

How awk processes lines and fields
Patterns and actions
Variables, operators and functions
Formatted output
Looping and branching in awk

Putting it all together