Shell Scripting (4 day)

Course Overview

Regular users of UNIX know that using advanced commands, shell features and shell scripts, improves efficiency and productivity as well as enhancing their use of Unix. Most users discover these capabilities in an ad-hoc and inefficient way, learning by trial and error and without understanding the concepts behind the features they use. This course focuses on the capabilities of the UNIX shell and the utilities commonly used in the development of shell scripts, interpreted programs.

The course is run using the Korn shell, a superset of the original UNIX Bourne shell, which is rapidly becoming the shell of choice for most users. Korn-only features are highlighted at each stage, making this course suitable for users of either shell. Having said that, those that use BASH (typically on Linux) should consider attending the (QALXBASH) Mastering BASH scripting course instead.

The course concentrates on the common approach to the variants of UNIX while looking at some specific areas of various systems and shells, and is particularly suitable for companies which take a multi-vendor open systems view, and is applicable to all flavours of Unix including Linux, HP-UX, UnixWare, Solaris, AIX, etc. The platform used for practical exercises is Linux.

All lectures have an accompanying practical session relating not only to the newly-covered material, but building on material and solutions from earlier sessions allowing realistic examples to be considered. The practical sessions account for approximately half of the course time. Hard copy and on-line solutions to all exercises are provided. Practical exercise component includes an optional project, which implements a solution for automated data backup over a network. Full solution to this project is also provided.

Course Outline

Introduction

• What is a shell?: Types of shell

Review

• Redirection and pipes
• Wildcards
• Creating shell scripts
• The .profile file
• Grouping commands and background execution

Overview

• Tilde expansion
• The whence command
• Quoting
• Using aliases
• The ENV file
• Here documents
• Job control

Variables

• Setting and getting variables
• Using ${} and $()
• Exported, read only and predefined variables
• Length of variables

Parameters

• Positional parameters
• Counting parameters
• Using shift
• Parameters and set

Making Decisions

• Exit status
• If-then
• If-then-else
• If-then-elif-then-else
• Tests
• The case statement
• Logical tests
• More pattern matching

Loops

• The while and until loops
• The for loop
• Break and continue
• The select command
• I/O redirection and loops
• The getopts command

Arithmetic in the Shell

• Declaring integer variables
• Operators
• The let keyword
• Making arithmetic tests
• Using other bases

Functions

• Writing functions
• Return values from functions
• Autoload
• Local versus global variables
• Listing and removing functions

Debugging in the Shell

• Setting the xtrace option
• The trace prompt
• Tracing functions
• Traps

Handling Arrays

• Accessing elements
• Setting elements
• Counting the elements in an array

Professional Scripts

• Organising project files
• Enhancing script behaviour with getopts

More Complicated I/O

• Putting files onto file descriptors
• Read and print revisited
• Co-processes

Introduction to sed and awk

• Simple instructions
• Script files
• Regular expressions
• Addressing in sed
• Grouping commands in sed
• The main awk loop
• Referencing fields
• Predefined awk values
• Variables, operators