BASH/C3/Basics-of-functions/English-timed
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Revision as of 00:13, 6 July 2015 by Sandhya.np14 (Talk | contribs)
Time | Narration |
00.01 | Dear friends, welcome to the spoken tutorial on Basics of functions in Bash. |
00.08 | In this tutorial, we will learn: |
00.11 | * Importance of Functions |
00.13 | * To declare a function |
00.15 | * To call a function |
00.17 | * Work flow of a function |
00.19 | with the help of an example. |
00.22 | To follow this tutorial, you should have knowledge of Shell Scripting in BASH. |
00.28 | If not, for relevant tutorials, please visit our website which is as shown. http://www.spoken-tutorial.org |
00.34 | For this tutorial, I am using Ubuntu Linux 12.04 Operating System. |
00.40 | Till now we were using GNU BASH version 4.1.10 |
00.46 | From now onwards, we will use GNU BASH version 4.2 |
00.52 | Please note, GNU Bash version 4 or above is recommended for practice. |
00.58 | Let us see what is a function and its usage. |
01.03 | A function is a collection of commands or an algorithm. |
01.08 | It is intended to do a specific task. |
01.12 | It is used to break up a complex program into separate tasks. |
01.18 | This improves overall script readability and ease of use. |
01.24 | There are two syntaxes for function declaration. |
01.28 | First syntax is- |
01.29 | function space function underscore name |
01.32 | within curly brackets, |
01.34 | the commands to be executed. |
01.37 | The second syntax is- |
01.39 | function underscore name open and close round brackets |
01.42 | within curly barckets, |
01.44 | the commands to be executed. |
01.47 | Function call- |
01.48 | Function can be called anywhere within the program. |
01.53 | Type the function name at the location where you want to call it. |
01.58 | The syntax is the function name itself. |
02.02 | Let us understand this with the help of a simple example. |
02.07 | I have already typed the code in a file function.sh. |
02.12 | This is the shebang line. |
02.14 | Function is declared by the keyword function followed by function name. |
02.21 | Here, function name is machine. |
02.26 | The content within curly brackets is called function definition. |
02.32 | I have displayed various machine details like- |
02.36 | uname hyphen a gives machine information. |
02.41 | w hyphen h gives users logged onto system. |
02.46 | uptime gives the time since machine was on. |
02.51 | free gives memory status. |
02.54 | df hyphen h gives filesystem status. |
02.57 | The main program starts here. |
03.01 | We display the message “Beginning of main program” . |
03.06 | Here, machine is a function call. |
03.09 | Then we display the message “End of main program”. |
03.13 | Let us understand the workflow. |
03.16 | # When the bash interpreter visits the function definition, it simply scans the function. |
03.23 | # The function is called only when its name appears within the script. |
03.28 | # When the interpreter reads the function name, it executes the function definition. |
03.36 | The interpreter treats function name as a command. |
03.41 | Please remember that we have to define the function before calling it. |
03.47 | Now go to the terminal. To make this code file executable, |
03.52 | type: chmod space plus x space function dot sh |
03.59 | Press Enter. |
04.01 | Type: dot slash function dot sh |
04.05 | Press Enter. |
04.07 | The output that is the machine details of my system are seen on the terminal. |
04.14 | Please Note: The output will vary from system to system. |
04.19 | This brings us to the end of this tutorial. |
04.22 | Come back to our slides. |
04.24 | Let us summarize. |
04.25 | In this tutorial, we learned: |
04.28 | * Importance of functions |
04.30 | * Function declaration |
04.32 | * Function call |
04.33 | * Work flow of function |
04.35 | with an example. |
04.37 | As an assignment- |
04.38 | write a program with two functions. |
04.42 | # The first function should display the disks-pace usage in human readable form (Hint: df hyphen h). |
04.51 | # The second function should display filesystem usage in human readable form (Hint: du hyphen h). |
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05.47 | The script has been contributed by FOSSEE and spoken-tutorial team. |
05.52 | This is Ashwini Patil from IIT Bombay, signing off. |
05.56 | Thank you for joining. |