Introduction To Shell Scripting

A shell is an interpreter in UNIX like Operating system. It takes commands typed by the user and calls the operating system to run those commands. In simple terms a shell acts as form of wrapper around the OS.

An Operating is made of many components, but its two prime components are –

Kernel

Shell

A Kernel is at the nucleus of a computer. It makes the communication between the hardware and…

Mgr1: Yes.

Eng1: Cool. I'll come find you.

Mgr1: Overdue parking fines?

Eng1: No. Unreturned library books.

Unix .ksh Script

Korn Shell (.ksh) is a Unix scripting programing language that can be used to automate a variety of tasks

Starting Out

The first line of any Korn Shell Script should be:

#!/bin/ksh

A comment can be made by using "#":

# This is a comment

It is considered to be best practice to leave comments in your script. Your comments should denote what particular functions or sections of your script are doing. In general, it is good to standardize the header of your script with

Script Name

Script Author(s)

Date of Creation

Purpose/Description of Script

*I personally like to write out any variables that I will be defining, or any variables that may be passed through the invokation of the script

######################## # # Script Name: Example Unix Korn Shell Script # Script Author: Daniel Robles # Date of Creation: 2013-07-09 # Description: This script illustrates basic Korn Schell Scripting # Variables: TBD # ########################

Time for some code! In this piece of code we will be sending an email to a user entered email address

#### #Tell the user what you would like them to do echo "Enter an Email Address: " #### #Tell the system to expect input from the user and assign the input to EMAIL_ADDRESS (referenced later by $EMAIL_ADDRESS) read EMAIL_ADDRESS #### #Create a variable called DATE (referenced later by $DATE) and assign it the value of of today DATE=$(date) #### #Create a variable called MESSAGE (referenced later by $MESSAGE) and assign it the string below with the referenced variables MESSAGE="Hello $email_address, The date is: $thedate" #### #Save the message in a file called MESSAGE.txt echo $MESSAGE > MESSAGE.txt #### #Invoke the Unix command "mail" to send an email # -s indicates a subject line will follow # the next parameter is the email address entered by the user # the next parameter tells the mail command to send the contents of MESSAGE.txt as the body of the email mail -s "Automated Email" $EMAIL_ADDRESS < MESSAGE.txt

What sort of tasks can be performed using a script like this?

Setup a cron job to run the script during specific time periods

Create notifications for completed jobs or system information

Automate repeated SQL jobs

Automate system chores

Automate file transfers