Difference between revisions of "BASH/C3/Basics-of-functions/English"

• Importance of Functions
• To declare a function
• To call a function
• Work flow of a function
• with the help of an example

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System requirements

Till now we were using GNU BASH version 4.1.10

From now onwards, we will use GNU BASH version 4.2

Please note, GNU Bash version 4 or above is recommended for practice.

Functions

• A function is a collection of commands or an algorithm.
• It is intended to do a specific task.
• It is used to break up a complex program into separate tasks.
• This improves overall script readability and ease of use.

Function declaration Syntax 1:

function function_name { Commands }

function space function_name

within curly brackets,

the commands to be executed

Function declaration Syntax 2:

function_name() { Commands }

function_name open and close round brackets

within curly barckets,

the commands to be executed

Function call

Function_name

Function can be called anywhere within the program.

Type the function name at the location where you want to call it.

The syntax is the function name itself.

function machine

#Function declaration

Here, function name is machine.

# Beginning of Function definition

echo -e "\nMachine information:" ; uname -a

echo -e "\nUsers logged on:" ; w -h

echo -e "\nMachine status :" ; uptime

echo -e "\nMemory status :" ; free

echo -e "\nFilesystem status :"; df -h

# End of Function definition

}

I have displayed various machine details like-

uname -a gives machine information.

w -h gives users logged onto system.

uptime gives the time since machine was on.

free gives memory status.

df -h gives filesystem status.

echo “Beginning of main program”

Here we display the message

“Beginning of main program”

“End of main program”

Workflow

1. When the bash interpreter visits the function definition, it simply scans the function.
2. The function is called only when its name appears within the script.
3. When the interpreter reads the function name, it executes the function definition.

Workflow

The interperter treats function name as a command.

Please remember that we have to define the function before calling it.

To make this code file executable, type:

chmod space plus x space function.sh

Press Enter.

Press Enter.

[Output]

Please Note: The output will vary from system to system.

This brings us to the end of this tutorial.

Come back to our slides.

Summary

In this tutorial we learnt,

• Importance of functions
• Function declaration
• Function call
• Work flow of function
• with an example

Assignment

Write a program with two functions

1. The first function should display the diskspace usage in human readable form(Hint: df -h)
2. The second function should display the filesystem usage in human readable form(Hint: du -h)

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About the Spoken Tutorial Project

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Acknowledgement

It is supported by the National Mission on Education through ICT, MHRD, Government of India

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro

This is Ashwini Patil from IIT Bombay.

Signing off

Thank you for joining.