Difference between revisions of "BASH/C2/Basics-of-Shell-Scripting/English-timed"
From Script | Spoken-Tutorial
Sandhya.np14 (Talk | contribs) |
Sandhya.np14 (Talk | contribs) |
||
| Line 604: | Line 604: | ||
|- | |- | ||
| 10:51 | | 10:51 | ||
| − | | | + | | {Hint: '''read -(Hyphen)t 10 -(Hyphen)p'''} |
|- | |- | ||
Revision as of 08:29, 2 July 2015
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on Basics of Shell Scripting. |
| 00:05 | In this tutorial, we will learn about: |
| 00:09 | * System variables |
| 00:11 | * User defined variables and |
| 00:13 | * Accepting user input via keyboard. |
| 00:16 | To follow this tutorial, you should be familiar with Linux Operating System. |
| 00:23 | If not, for relevant tutorials please visit our website which is as shown. |
| 00:29 | For this tutorial, I am using: |
| 00:32 | * Ubuntu Linux 12.04 Operating System and |
| 00:35 | * GNU Bash version 4.1.10 |
| 00:40 | Please NoteGNU Bash version 4 or above is recommended for practice. |
| 00:46 | Let us start with an introduction to variables. |
| 00:49 | * Bash variables provide temporary storage for information. |
| 00:55 | * These variables can be used within the lifespan of the program. |
| 01:01 | * There are two types of variables:
|
| 01:07 | System variables: These are created and maintained by Linux Bash Shell itself. |
| 01:14 | They are defined by capital letters. |
| 01:17 | Commonly used system variables are- |
| 01:20 | * BASH_VERSION |
| 01:21 | * HOSTNAME |
| 01:23 | * HOME etc. |
| 01:25 | Let us open the terminal by pressing Ctrl Alt and T keys simultaneously on your keyboard. |
| 01:33 | Now, type: set and press Enter. |
| 01:38 | This will display all the system variables. |
| 01:42 | Alternately, you can type env or printenv to view all the system variables. |
| 01:53 | Let me clear the prompt. |
| 01:55 | Now, type: echo space within double quotes dollar sign HOSTNAME. |
| 02:01 | and now press Enter. |
| 02:04 | The hostname of the system will be displayed. |
| 02:07 | Now let's find out the full path of homedirectory. |
| 02:11 | Type: echo space within double quotes dollar sign HOME(in capital). |
| 02:18 | Press Enter. |
| 02:21 | The full path of user's home directory will be displayed. |
| 02:26 | Now, type: |
| 02:27 | echo space within double quotes HOME (in capital). |
| 02:32 | Press Enter. |
| 02:34 | This will display only the HOME not the value of HOME variable. |
| 02:39 | So, it is necessary to use dollar sign( '$') at the beginning of every variable to display its value. |
| 02:48 | Let us switch back to our slides. |
| 02:51 | User Defined Variables: |
| 02:53 | * These variables are created and maintained by users. |
| 02:57 | * It is always a good idea to avoid uppercase for the names of user defined variables. |
| 03:05 | * This makes it easy to differentiate between user defined and system variables. |
| 03:12 | Switch back to our terminal. |
| 03:14 | Type: username equal to sign sunita. |
| 03:20 | Please note that there should not be any blank space between username, equal to sign and sunita. |
| 03:29 | Now, press Enter. |
| 03:30 | To display the value of variable username, |
| 03:33 | Type: echo space within double quotes dollar sign username. |
| 03:40 | press Enter. |
| 03:42 | This will display sunita on your terminal. |
| 03:46 | The value of a variable can be unset. |
| 03:50 | Let us switch back to our slide. |
| 03:52 | unset- the value of variable can be unset by using the unset command. |
| 03:59 | The syntax for this is- unset variablename |
| 04:03 | Let's use the previous example where username is our variable. |
| 04:08 | Switch to the Terminal. Now type: unset space username, press Enter. |
| 04:18 | Let us check. Type: echo space within double quotes dollar sign username , press Enter. |
| 04:28 | Nothing will be displayed on the terminal. |
| 04:30 | This means that the value of variable username has been removed. |
| 04:36 | Now switch back to our slide. |
| 04:39 | Global and local variables: |
| 04:42 | * In Shell script, user defined variables can be declared globally or locally. |
| 04:49 | * By default, all variables are global. |
| 04:52 | * This means, their values remain the same inside and outside the function. |
| 04:59 | Let us learn how to declare variables globally and locally. |
| 05:04 | Switch to the terminal and type: |
| 05:07 | gedit space g_(underscore)variable.sh space & (ampersand sign). |
| 05:16 | gedit is the text editor g_(underscore) variable.sh is our file name |
| 05:23 | and & (ampersand) is used to free up the prompt. |
| 05:28 | Press Enter. |
| 05:30 | Type the code as shown here, in your g_(underscore)variable.sh file. |
| 05:35 | Let me explain the code now. |
| 05:38 | The first line with the hash and exclamation symbol, is a shebang or a bang line. |
| 05:44 | username=sunita is the userdefined variable and it is declared globally. |
| 05:51 | echo will display the string outside function: and |
| 05:55 | dollar username will print the value of the variable username. |
| 06:00 | This is how we defined a function in BASH script. |
| 06:04 | We will discuss about functions in detail, in later tutorials. |
| 06:09 | This is the body of the function. |
| 06:12 | Here another message inside function will be displayed, along with the value of username. |
| 06:19 | Here, we call the function. |
| 06:21 | This is our code. Now let's execute it. |
| 06:23 | Come back to our Terminal. |
| 06:26 | Let me clear the prompt. |
| 06:28 | First we need to make our file executable. |
| 06:31 | Type: chmod space plus x space g_(underscore)variable.sh, press Enter. |
| 06:39 | Now type: dot slash g_(Underscore)variable.sh |
| 06:45 | Press Enter. |
| 06:47 | Observe the output. |
| 06:48 | Outside the function, username takes the value sunita. |
| 06:53 | Inside the function also, username takes the same value sunita. |
| 06:59 | This is because username was declared globally outside the function. |
| 07:04 | Next, let us learn how to declare a variable locally. |
| 07:09 | Type: gedit space l_(Underscore)variable.sh space & (ampersand sign). |
| 07:18 | Press Enter. |
| 07:20 | Type the code as shown here, in your l_(underscore)variable.sh file. |
| 07:25 | Let me explain the code. |
| 07:28 | The code is the same as before, except for an extra line of code inside the function. |
| 07:36 | Inside the function block, we have a line-local space username equals to jack |
| 07:41 | This assigns a new value for the variable username locally. |
| 07:48 | Now switch to the Terminal. |
| 07:50 | Let's make file executable. |
| 07:52 | By typing chmod space plus x space l_variable.sh |
| 08:00 | Press Enter. |
| 08:02 | Type: dot slash l_variable.sh |
| 08:07 | Press Enter. |
| 08:08 | The output is displayed. |
| 08:10 | Outside the function, username takes the value sunita |
| 08:15 | whereas inside the function, username takes the value jack. |
| 08:20 | This is because username is assigned this value locally, within the function. |
| 08:26 | Now let us quickly see how to get user input via keyboard. |
| 08:31 | The read command is used to accept input from the keyboard. |
| 08:36 | It can also be used to assign an input value to a user defined variable. |
| 08:41 | The syntax of read command is- |
| 08:44 | read space hyphen p space within double quotes PROMPT |
| 08:50 | Please note that PROMPT is just a string that waits for user input. |
| 08:55 | You may replace it with your own string. |
| 08:58 | Now, switch to the terminal . |
| 09:00 | Type: gedit space read.sh space & (ampersand sign) |
| 09:08 | Press Enter. |
| 09:09 | Type the code as shown in your read.sh file. |
| 09:14 | Let me explain the code. |
| 09:16 | In this example, input is given from the keyboard by the user. |
| 09:21 | This is the bang line. |
| 09:23 | Here -p displays the prompt without a newline and takes input from the keyboard. |
| 09:31 | The user input will be stored in the variable username. |
| 09:36 | echo command displays the message |
| 09:38 | Hello and the name entered by the user via the keyboard. |
| 09:43 | So, let us execute the program. |
| 09:45 | Come back to our terminal. |
| 09:49 | Type: chmod space plus x space read.sh |
| 09:55 | press Enter. |
| 09:56 | Type: dot slash read.sh press Enter. |
| 10:01 | Here it is displayed Enter username: |
| 10:04 | I will type ashwini, press Enter. |
| 10:08 | The message Hello ashwini is displayed. |
| 10:13 | ashwini was assigned as an input value to the user defined variable username. |
| 10:20 | Let us go back to our slide and summarize. |
| 10:23 | In this tutorial, we learnt: |
| 10:26 | * System variables |
| 10:27 | * User defined variables |
| 10:29 | * Accepting user input via keyboard. |
| 10:33 | As an assignment- |
| 10:34 | Write a simple Bash program to get the following system variables. |
| 10:38 | * pwd and * logname. |
| 10:41 | * Write a simple Bash program |
| 10:43 | to ask username from user |
| 10:46 | to exit the program, if user does not enter anything within 10 seconds. |
| 10:51 | {Hint: read -(Hyphen)t 10 -(Hyphen)p} |
| 10:56 | Watch the video available at the link shown below. |
| 10:59 | It summarizes the Spoken-Tutorial project. |
| 11:02 | If you do not have good bandwidth, you can download and watch it. |
| 11:07 | The Spoken Tutorial Project team: Conducts workshops using spoken tutorials.
Gives certificates to those who pass an online test. |
| 11:16 | For more details, please write to contact@spoken-tutorial.org |
| 11:23 | Spoken Tutorial Project is a part of the "Talk to a Teacher" project. |
| 11:27 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 11:34 | More information on this mission is available at the link shown below: http://spoken-tutorial.org\NMEICT-Intro |
| 11:40 | The script has been contributed by FOSSEE and Spoken Tutorial teams. |
| 11:44 | This is Ashwini Patil from IIT Bombay, signing off. Thank you for joining. |
