Open main menu

CDOT Wiki β

Tutorial10: Shell Scripting - Part 1

Revision as of 08:42, 9 July 2020 by Msaul (talk | contribs) (Creating & Executing Shell Scripts)

INTRODUCTION TO SHELL SCRIPTING


Main Objectives of this Practice Tutorial

  • Understand the process for planning prior to writing a shell script.
  • Understand the purpose of a she-bang line contained at the top of a shell script.
  • Setting permissions for a shell script and properly execute a shell script.
  • Understand and use environment and user-defined variables within a shell script.
  • Understand the purpose of control flow statements used with shell scripts.
  • Use the test command to test various conditions.
  • Use the if logic statement and the for loop statement within shell scripts.

Tutorial Reference Material

Course Notes
Linux Command/Shortcut Reference
YouTube Videos
Course Notes:


Shell Scripting
  • Purpose
  • Planning a Shell Script
  • Executing a Shell Script

Variables

  • Environment
  • User Defined
Control Flow Statements
  • Purpose
  • test command
  • if statement
  • for loop
Brauer Instructional Videos:

KEY CONCEPTS

A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter.
The various dialects of shell scripts are considered to be scripting languages.

Reference: https://en.wikipedia.org/wiki/Shell_script

Creating & Executing Shell Scripts

 
An IPSO Diagram (INPUT, PROCESSING, STORAGE, OUTPUT) can be used to map-out and then list the sequence of steps to assist when coding your shell script.

It is recommended to plan out on a piece of paper the purpose of the shell script.
You can do this by creating a simple IPSO diagram (stands for INPUT, PROCESSING, STORAGE, OUTPUT).

First, list the INPUTS into the script (eg. prompting user for data, reading data from file, etc), then listing the expected OUTPUTS from the script. You can then list the steps to process the INPUT to provide the OUTPUT (including file storage).

Once you have planned your shell script by listing the sequence of steps in your script, you need to create a file that will contain your Linux commands. NOTE: Avoid using filenames of already existing Linux Commands to avoid confusion. Using shell script filenames that include the file extension of the shell that the script will run within is recommended.

Using a Shebang Line

 
The shebang line must appear on the first line and at the beginning of the shell script.
If you are learning Bash scripting by reading other people’s code you might have noticed
that the first line in the scripts starts with the #! characters and the path to the Bash interpreter.


This sequence of characters (#!) is called shebang and is used to tell the operating system
which interpreter to use to parse the rest of the file. Reference: https://linuxize.com/post/bash-shebang/

The shebang line must appear on the first line and at the beginning of the shell script, otherwise, it will be treated as a regular comment and ignored.

Setting Permissions & Running a Shell Script

x

Using Variables in Shell Scripts

x


Using Control Flow Statements in Shell Scripts

x

INVESTIGATION 1: CREATING A SHELL SCRIPT


In this section, you will learn how to ...



Perform the Following Steps:

  1. x

In the next investigation, you will ...

INVESTIGATION 2: USING VARIABLES IN SHELL SCRIPTS

In this section, you will learn how to ...


Perform the Following Steps:

  1. x

In the next investigation, you will ...

INVESTIGATION 3: USING CONTROL FLOW STATEMENTS IN SHELL SCRIPTS

In this section, you will learn how to ...


Perform the Following Steps:

  1. x

LINUX PRACTICE QUESTIONS

The purpose of this section is to obtain extra practice to help with quizzes, your midterm, and your final exam.

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week10_practice.docx

Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).


Review Questions:

  1. x
  2. x
  3. x
  4. x
  5. x
  6. x
  7. x
  8. x