Shell Scripting

Table of Contents

1. Tour de Shell Scripting

Introduction to the Course structure

Adage 1.0:

What you will need

What is Shell Scripting

Introduction to info, man and the whatis database

info pages

Man Pages

The whatis Database

Revising some Basic Commands

The who command

The w Command

The "date" command

The 'echo' command

File Commands

System Commands

stdin, stdout, stderr

stdin

stdout

Using stdin and stdout simultaneously

Appending to a file

stderr

stdout, stderr and using the ampersand (&)

Exercises:

Unamed Pipes

2. The Shell

Introduction

What is the login shell?

Exercises

The job of the shell

Command Interpreter

Allows for variables to be set

I/O redirection

Pipelines

Customising your environment

Conclusion:

3. Regular Expressions

Introduction

What are regular expressions?

The fullstop

Let's explore "sed" syntax

Square brackets ( [ ] ), the caret ( ^ ) and the dollar ( $ )

Using sed and pipes

The splat (asterisk) ( * )

The plus operator ( + )

Returning from detour to our discussion on curly braces …

RE's are greedy for matching patterns

Placeholders and word boundaries

Word boundaries ( < and > ) - a formal explanation

The tr command

The cut command

First Example in stages:

Second Example in stages:

Third example in stages

Exercises:

The paste command

The uniq command

The Sort command

The grep command

grep, egrep and fgrep

Exercises:

Challenge sequence:

4. Practically Shell Scripting

Section Techniques to use when writing, saving and executing Shell Scripts

Detour: File Extension labels

Comments in scripts

Variables

Shebang or hashpling #!

Exit

Null and unset variables

Variable Expansion

Environmental vs shell variables

Arithmetic in the shell

Examples

Exercises:

5. Using Quotation marks in the Shell

Introduction

Single Quotes or "ticks"

Exercises:

Double Quotes

Exercises

Backticks

Exercises:

Shell Arithmetic's with expr and back quotes

Another tip when using quotation marks

6. So, you want an Argument?

Introduction

Positional Parameters 0 and 1 through 9

Exercises:

Challenge sequence:

Other arguments used with positional parameters

$# How many positional arguments have we got ?

$* - display all positional parameters

Using the "shift" command - for more than 9 positional parameters

Exit status of the previous command

7. Where to From Here?

Making Decisions

Testing for a true or false condition

Different types of tests

Logical Operators

Exercises:

Conditions in the shell

Using the "if" statement

The "if" "then" "else" statement

The "elif" statement

The "case" statement

Exercises

Challenge sequence:

Debugging your scripts

The NULL command

The || and && commands

Exercises:

8. Loops

Introduction

The "for" loop

while and until loops

getopts Using arguments and parameters

Exercises:

9. User input to a script

Introduction

The read command

Presenting the output

The echo command

The printf command

10. Additional Information

The shell environmental variables pertaining to scripting

The Source command

Exercises:

the exec command

Other methods of executing a script or a series of commands

11. Positional parameters & variables re-visited

Introduction

PARAM:-value

PARAM:=value

${param:+value}

?${variable%pattern}

MAGIC%%r*a

variable#pattern

variable:OFFSET:LENGTH

#variable

Re-assigning parameters with set

Explaining the default field separator field - IFS

Setting variables as "readonly"

Exercises:

Challenge sequences:

12. Bits and pieces - tying up the loose ends

The eval command

Running commands in the background using &

Traps and signals

Signals

Traps

Exercises:

File descriptors re-visited

Exercises

Here documents

Exercises

Functions

Exercises:

Challenge sequence

A. Writing html pages

B. An introduction to dialog

C. A Comparisson of bash, tsch and ksh

Index