Difference between revisions of "BASH/C3/More-on-functions/English-timed"
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| − | | In a similar manner, I will '''call''' the same '''function''' with a different set of '''arguments'''. So, I have'''say_welcome''' space within double quotes '''functions in''' space within double quotes '''Bash'''. | + | | In a similar manner, I will '''call''' the same '''function''' with a different set of '''arguments'''. So, I have''' say_welcome''' space within double quotes '''functions in''' space within double quotes '''Bash'''. |
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Revision as of 11:00, 14 July 2015
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on More on functions. |
| 00:06 | In this tutorial, we will learn: |
| 00:09 | * To pass an argument to a function; |
| 00:11 | * To define local variable within a function and |
| 00:16 | * To define global variable in a function |
| 00:19 | with the help of some examples. |
| 00:23 | 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) |
| 00:35 | For this tutorial, I am using: |
| 00:37 | * Ubuntu Linux 12.04 Operating System |
| 00:42 | * GNU BASH version 4.2. |
| 00:45 | Please note, GNU Bash version 4 or above is recommended to practice this tutorial. |
| 00:52 | Let us first learn how to pass an argument to a function and its usage. |
| 00:59 | Let me open a file 'function_(underscore) parameters.sh' . |
| 01:05 | This is the shebang line. |
| 01:08 | Our function name is say_(underscore)welcome. |
| 01:13 | Open curly bracket opens the function definition. |
| 01:18 | '$1' (Dollar one) is the first positional parameter. |
| 01:22 | '$2' (Dollar two) is the second positional parameter. |
| 01:26 | Close curly bracket closes the function definition. |
| 01:30 | Here, the function 'say_welcome' is called with arguments. |
| 01:35 | The syntax is- function name i.e. "say_welcome" followed by the arguments within double quotes, i.e. "Bash" and "learning". |
| 01:49 | In a similar manner, I will call the same function with a different set of arguments. So, I have say_welcome space within double quotes functions in space within double quotes Bash. |
| 02:05 | Save the file and go to the terminal. |
| 02:08 | Type: chmod space plus x space function underscore parameters dot sh. |
| 02:17 | Press Enter. |
| 02:19 | Type: dot slash function underscore parameters dot sh. |
| 02:26 | Press Enter. |
| 02:28 | We see that the positional parameters were substituted by the arguments passed to a function. |
| 02:36 | Dollar 1 ($1) was substituted by the string "Bash" and Dollar 2 ($2) with "learning". |
| 02:45 | Then again, Dollar 1 ($1) was substituted by "functions in" and Dollar 2 ($2) with "Bash". |
| 02:55 | In Bash, variables can be declared as local variables and global variables. |
| 03:01 | Local variable: |
| 03:03 | * Its value will be valid within the function in which it is defined. |
| 03:10 | * Local variables are declared using keyword local. |
| 03:15 | Global variable: |
| 03:17 | The value of a global variable can be accessed throughout a Bash script. |
| 03:24 | Let us learn these 2 ways to declare a variable within a function. |
| 03:29 | Let me open a file named 'function_(underscore)local.sh'. |
| 03:35 | This is the shebang line. |
| 03:39 | Function name is say_(underscore) hello. |
| 03:43 | Here, variable first_name is declared with keyword local |
| 03:49 | which means its value will be valid within the function say_hello only. |
| 03:55 | A variable declared without any keyword is treated as a global variable. |
| 04:01 | So, the variable last_name can be accessed throughout the script. |
| 04:08 | In this echo line, we will display the value of variables |
| 04:12 | first_name, |
| 04:14 | middle_name |
| 04:15 | and last_name. |
| 04:17 | After this, we close the function. |
| 04:21 | Now, here, the variable middle_name is declared without keyword. So, its value will be global throughout the script. |
| 04:30 | Once again, we call the function here. |
| 04:34 | We pass two arguments to this function call namely- “Pratik” and “Patil”. |
| 04:41 | These echo statements will display the value of variables- |
| 04:45 | $first_name, |
| 04:46 | $middle_name and $last_name. |
| 04:51 | Please keep in mind that variable first_name is a local variable. |
| 04:57 | Save the file and go to the terminal. |
| 05:00 | Type: chmod space plus x space function underscore local dot sh. |
| 05:09 | Press Enter. |
| 05:11 | Type: dot slash function underscore local dot sh |
| 05:16 | Press Enter. |
| 05:18 | The first line of output displays the message "Hello Pratik K Patil". |
| 05:25 | Here, the variable first_name that contains value "Pratik" is local |
| 05:31 | which means the value is limited to the function. |
| 05:35 | Now, let us see how the local variable behaves outside the function. |
| 05:41 | Here, nothing is displayed in first_name. |
| 05:44 | This is because the value of first_name is local to the function. And it is not available outside the function. |
| 05:53 | middle_name and last_name are printed as they are global variables. |
| 05:59 | Hope the difference is clear to you. |
| 06:02 | Let us now summarize. |
| 06:04 | In this tutorial, we learned: |
| 06:07 | * To pass arguments to a function;
|
| 06:14 | * To declare global variable in a function with the help of a few examples. |
| 06:20 | As an assignment- |
| 06:22 | write a program |
| 06:23 | where the function accepts two arguments. The function should multiply the two arguments. |
| 06:31 | Make 3 function calls with arguments (1, 2), (2, 3) and (3, 4). |
| 06:39 | Watch the video available at the link shown below. |
| 06:43 | It summarizes the Spoken-Tutorial project. If you do not have good bandwidth, you can download and watch it. |
| 06:51 | The Spoken Tutorial Project team:
|
| 07:00 | For more details, please write to contact@spoken-tutorial.org |
| 07:07 | Spoken Tutorial project is a part of the Talk to a Teacher project. |
| 07:11 | 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 |
| 07:26 | The script has been contributed by FOSSEE and Spoken-Tutorial teams. |
| 07:31 | This is Ashwini Patil from IIT Bombay, signing off. Thank you for joining. |
