Difference between revisions of "BASH/C2/Logical-Operators/English-timed"
From Script | Spoken-Tutorial
Sandhya.np14 (Talk | contribs) |
Sandhya.np14 (Talk | contribs) |
||
| Line 8: | Line 8: | ||
|- | |- | ||
| 00:01 | | 00:01 | ||
| − | | Dear friends, | + | | Dear friends, welcome to the Spoken tutorial on '''Logical Operators''' in '''Bash'''. |
|- | |- | ||
| 00:07 | | 00:07 | ||
| − | | In this tutorial, we will learn | + | | In this tutorial, we will learn use of: |
|- | |- | ||
| 00:10 | | 00:10 | ||
| − | | * | + | |* '''Logical AND''' |
* '''Logical OR''' | * '''Logical OR''' | ||
* '''Logical NOT''' | * '''Logical NOT''' | ||
| − | + | using a few examples. | |
|- | |- | ||
| 00:19 | | 00:19 | ||
| − | | To follow this tutorial you should have knowledge of | + | | To follow this tutorial, you should have knowledge of: |
|- | |- | ||
| 00:22 | | 00:22 | ||
| − | | * '''if-else statement | + | |* '''if-else statement''' |
* '''command line arguments '''and | * '''command line arguments '''and | ||
* '''quoting '''in''' BASH.''' | * '''quoting '''in''' BASH.''' | ||
| Line 33: | Line 33: | ||
|- | |- | ||
| 00:30 | | 00:30 | ||
| − | | If not, for relevant tutorials, please visit our website | + | | If not, for relevant tutorials, please visit our website which is as shown. |
|- | |- | ||
| 00:36 | | 00:36 | ||
| − | | For this tutorial I am using | + | | For this tutorial, I am using: |
|- | |- | ||
| Line 49: | Line 49: | ||
|- | |- | ||
| 00:47 | | 00:47 | ||
| − | | '''GNU Bash''' version | + | | '''GNU Bash''' version 4 or above is recommended for practice. |
|- | |- | ||
| 00:53 | | 00:53 | ||
| − | | Let us understand the use of ''' Logical operators.''' | + | | Let us understand the use of ''' Logical-operators.''' |
|- | |- | ||
| 00:57 | | 00:57 | ||
| − | | | + | | '''Logical operators''' are mainly used to control program flow. |
|- | |- | ||
| 01:02 | | 01:02 | ||
| − | | | + | | '''Logical operators''' help to link two '''expressions''' or '''conditions'''. |
|- | |- | ||
| 01:09 | | 01:09 | ||
| − | | | + | | They can be a part of '''if, while''' or some other '''control statements'''. |
|- | |- | ||
| 01:15 | | 01:15 | ||
| − | | Let's see the syntax of '''logical AND''' | + | | Let's see the syntax of '''logical AND'''. |
|- | |- | ||
| 01:19 | | 01:19 | ||
| − | | | + | | '''Opening square bracket space dollar symbol '''condition1''' space closing square bracket space ampersand ampersand space opening square bracket space dollar symbol '''condition2''' space closing square bracket. |
|- | |- | ||
| 01:38 | | 01:38 | ||
| − | | | + | | Or we can use this syntax- |
|- | |- | ||
| 01:41 | | 01:41 | ||
| − | | | + | | Opening square bracket space dollar symbol '''condition1''' space hyphen '''a''' space dollar symbol '''condition2''' space closing square bracket. |
|- | |- | ||
| 01:53 | | 01:53 | ||
| − | | | + | | '''Logical AND''' returns '''True''' when both '''condition1''' and '''condition2''' are '''True'''. |
|- | |- | ||
| 02:00 | | 02:00 | ||
| − | | Let us see the syntax of '''Logical OR''' | + | | Let us see the syntax of '''Logical OR'''. |
|- | |- | ||
| 02:04 | | 02:04 | ||
| − | | | + | | Opening square bracket space dollar symbol '''condition1''' space closing square bracket space vertical bar again vertical bar space opening square bracket space dollar symbol '''condition2''' space closing square bracket. |
|- | |- | ||
| 02:22 | | 02:22 | ||
| − | | | + | | Or we can use this syntax- |
|- | |- | ||
| 02:24 | | 02:24 | ||
| − | | | + | | Opening square bracket space dollar symbol '''condition1''' space hyphen '''o''' space dollar symbol '''condition2''' space closing square bracket. |
|- | |- | ||
| 02:36 | | 02:36 | ||
| − | | | + | | '''Logical OR''' returns ''' True''' when either '''condition1''' or '''condition2''' is '''True'''. |
|- | |- | ||
| 02:43 | | 02:43 | ||
| − | | | + | | Let us learn the usage of ''' Logical OR''' and '''Logical AND''' using an example. |
|- | |- | ||
| 02:50 | | 02:50 | ||
| − | | I have already typed the code in a file named '''logical.sh'''. | + | | I have already typed the '''code''' in a file named '''logical.sh'''. |
|- | |- | ||
| 02:55 | | 02:55 | ||
| − | | Open the '''terminal''' by pressing '''ctrl+alt''' | + | | Open the '''terminal''' by pressing '''ctrl+alt''' and '''t''' keys simultaneously on your keyboard. |
|- | |- | ||
| 03:04 | | 03:04 | ||
| − | | Type: '''gedit space logical.sh space | + | | Type: '''gedit space logical.sh space ampersand''' sign press '''Enter.''' |
|- | |- | ||
| 03:12 | | 03:12 | ||
| − | | Now type the code as shown here in your ''' logical.sh''' file. | + | | Now type the code as shown here, in your ''' logical.sh''' file. |
|- | |- | ||
| 03:18 | | 03:18 | ||
| − | | Let me explain the code now. | + | | Let me explain the '''code''' now. |
|- | |- | ||
| Line 139: | Line 139: | ||
|- | |- | ||
| 03:29 | | 03:29 | ||
| − | | '''- (hyphen) p''' | + | | '''- (hyphen) p''' displays the '''prompt.''' |
|- | |- | ||
| Line 150: | Line 150: | ||
|- | |- | ||
| 03:45 | | 03:45 | ||
| − | | '''- (hyphen) z '''checks whether length of '''string''' is '''zero''' | + | | '''- (hyphen) z '''checks whether length of '''string''' is '''zero'''. |
|- | |- | ||
| 03:50 | | 03:50 | ||
| − | | Type '''man space test on ''' terminal''' to explore various other '''string | + | | Type: '''man space test''' on ''' terminal''' to explore various other '''string''' comparisons. |
|- | |- | ||
| Line 166: | Line 166: | ||
|- | |- | ||
| 04:08 | | 04:08 | ||
| − | | Here it checks whether the entered '''string''' contains both the words | + | | Here, it checks whether the entered '''string''' contains both the words ''' 'raj' '''and ''' 'jit' '''. |
|- | |- | ||
| Line 186: | Line 186: | ||
|- | |- | ||
| 04:37 | | 04:37 | ||
| − | | Here it checks whether the entered string contains either '''raj''' or '''jit.''' | + | | Here, it checks whether the entered '''string''' contains either '''raj''' or '''jit.''' |
|- | |- | ||
| Line 206: | Line 206: | ||
|- | |- | ||
| 05:02 | | 05:02 | ||
| − | | When all the above statements are | + | | When all the above statements are '''False''' then this statement will be executed. |
|- | |- | ||
| 05:08 | | 05:08 | ||
| − | | '''fi''' is the end of '''multilevel if-else''' loop. | + | | '''fi''' is the end of '''multilevel if-else''' '''loop'''. |
|- | |- | ||
| 05:12 | | 05:12 | ||
| − | | Let us execute the program | + | | Let us '''execute''' the program. |
|- | |- | ||
| Line 222: | Line 222: | ||
|- | |- | ||
| 05:17 | | 05:17 | ||
| − | | First make the file executable by typing- '''chmod space plus x space logical dot sh''' press Enter. | + | | First make the file executable by typing- '''chmod space plus x space logical dot sh''' press '''Enter'''. |
|- | |- | ||
| 05:30 | | 05:30 | ||
| − | | Now type '''dot slash logical.sh''' press '''Enter.''' | + | | Now type: '''dot slash logical.sh''' press '''Enter.''' |
|- | |- | ||
| Line 233: | Line 233: | ||
|- | |- | ||
| 05:38 | | 05:38 | ||
| − | | I will enter '''jitinraj''' | + | | I will enter '''jitinraj'''. |
|- | |- | ||
| 05:42 | | 05:42 | ||
| − | | The output is: '''jitinraj contains both the words raj and jit''' | + | | The '''output''' is: '''jitinraj contains both the words 'raj' and 'jit'. ''' |
|- | |- | ||
| 05:48 | | 05:48 | ||
| − | | This means that the control was passed to the second statement. | + | | This means that the control was passed to the second '''statement'''. |
|- | |- | ||
| Line 249: | Line 249: | ||
|- | |- | ||
| 05:57 | | 05:57 | ||
| − | | Now let us execute the script again. | + | | Now, let us '''execute''' the '''script''' again. |
|- | |- | ||
| 06:00 | | 06:00 | ||
| − | | Press the | + | | Press the '''up-arrow''' key. |
|- | |- | ||
| 06:02 | | 06:02 | ||
| − | | Go to | + | | Go to '''./logical.sh ''' press '''Enter'''. |
|- | |- | ||
| Line 273: | Line 273: | ||
|- | |- | ||
| 06:19 | | 06:19 | ||
| − | | Please try executing the program with different | + | | Please try executing the program with different '''input'''s and observe the '''output'''. |
|- | |- | ||
| Line 285: | Line 285: | ||
|- | |- | ||
| 06:31 | | 06:31 | ||
| − | | It inverts the ''' | + | | It inverts the '''Boolean''' value of an expression |
|- | |- | ||
| Line 305: | Line 305: | ||
|- | |- | ||
| 06:52 | | 06:52 | ||
| − | | | + | | or '''opening square bracket space exclamation mark space expression space closing square bracket'''. |
|- | |- | ||
| Line 433: | Line 433: | ||
|- | |- | ||
| 09:47 | | 09:47 | ||
| − | | | + | | check whether the file exists |
|- | |- | ||
Revision as of 15:48, 3 July 2015
Title of script: Logical Operators in Bash Author: Lavitha pereira Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT
| Time | Narration |
|---|---|
| 00:01 | Dear friends, welcome to the Spoken tutorial on Logical Operators in Bash. |
| 00:07 | In this tutorial, we will learn use of: |
| 00:10 | * Logical AND
using a few examples. |
| 00:19 | To follow this tutorial, you should have knowledge of: |
| 00:22 | * if-else statement
|
| 00:30 | If not, for relevant tutorials, please visit our website which is as shown. |
| 00:36 | For this tutorial, I am using: |
| 00:38 | * Ubuntu Linux 12.04 OS |
| 00:43 | * GNU Bash version 4.1.10 |
| 00:47 | GNU Bash version 4 or above is recommended for practice. |
| 00:53 | Let us understand the use of Logical-operators. |
| 00:57 | Logical operators are mainly used to control program flow. |
| 01:02 | Logical operators help to link two expressions or conditions. |
| 01:09 | They can be a part of if, while or some other control statements. |
| 01:15 | Let's see the syntax of logical AND. |
| 01:19 | Opening square bracket space dollar symbol condition1 space closing square bracket space ampersand ampersand space opening square bracket space dollar symbol condition2 space closing square bracket. |
| 01:38 | Or we can use this syntax- |
| 01:41 | Opening square bracket space dollar symbol condition1 space hyphen a space dollar symbol condition2 space closing square bracket. |
| 01:53 | Logical AND returns True when both condition1 and condition2 are True. |
| 02:00 | Let us see the syntax of Logical OR. |
| 02:04 | Opening square bracket space dollar symbol condition1 space closing square bracket space vertical bar again vertical bar space opening square bracket space dollar symbol condition2 space closing square bracket. |
| 02:22 | Or we can use this syntax- |
| 02:24 | Opening square bracket space dollar symbol condition1 space hyphen o space dollar symbol condition2 space closing square bracket. |
| 02:36 | Logical OR returns True when either condition1 or condition2 is True. |
| 02:43 | Let us learn the usage of Logical OR and Logical AND using an example. |
| 02:50 | I have already typed the code in a file named logical.sh. |
| 02:55 | Open the terminal by pressing ctrl+alt and t keys simultaneously on your keyboard. |
| 03:04 | Type: gedit space logical.sh space ampersand sign press Enter. |
| 03:12 | Now type the code as shown here, in your logical.sh file. |
| 03:18 | Let me explain the code now. |
| 03:21 | This is the shebang line. |
| 03:25 | The read command reads one line of data from standard input. |
| 03:29 | - (hyphen) p displays the prompt. |
| 03:33 | string is a variable which stores the text entered by the user, during execution. |
| 03:39 | The if statement checks whether the entered string is empty. |
| 03:45 | - (hyphen) z checks whether length of string is zero. |
| 03:50 | Type: man space test on terminal to explore various other string comparisons. |
| 03:57 | The echo statement will print a message if nothing was entered. |
| 04:02 | If the string is not empty, the program will move to the first elif statement. |
| 04:08 | Here, it checks whether the entered string contains both the words 'raj' and 'jit' . |
| 04:16 | If yes, then it echoes out a message. |
| 04:20 | Please note that logical AND is used here. |
| 04:24 | Hence, the message will be displayed only when both the conditions are satisfied. |
| 04:31 | If that is not so, then the program will move onto the second elif statement. |
| 04:37 | Here, it checks whether the entered string contains either raj or jit. |
| 04:43 | If yes, then it displays the message. |
| 04:47 | Please note that logical OR is used here. |
| 04:52 | The message will be displayed only when any one of the conditions are satisfied. |
| 04:59 | Lastly, we have the default else statement. |
| 05:02 | When all the above statements are False then this statement will be executed. |
| 05:08 | fi is the end of multilevel if-else loop. |
| 05:12 | Let us execute the program. |
| 05:15 | Switch back to the terminal. |
| 05:17 | First make the file executable by typing- chmod space plus x space logical dot sh press Enter. |
| 05:30 | Now type: dot slash logical.sh press Enter. |
| 05:36 | The prompt displays Enter a word: |
| 05:38 | I will enter jitinraj. |
| 05:42 | The output is: jitinraj contains both the words 'raj' and 'jit'. |
| 05:48 | This means that the control was passed to the second statement. |
| 05:52 | And as both the conditions are satisfied, it displays the message. |
| 05:57 | Now, let us execute the script again. |
| 06:00 | Press the up-arrow key. |
| 06:02 | Go to ./logical.sh press Enter. |
| 06:07 | The prompt displays Enter a word: |
| 06:09 | This time I will enter abhijit. |
| 06:13 | The output is displayed as: abhijit contains word 'raj' or 'jit'. |
| 06:19 | Please try executing the program with different inputs and observe the output. |
| 06:25 | Let's switch back to our slides. |
| 06:27 | Let's have a look at logical NOT operator. |
| 06:31 | It inverts the Boolean value of an expression |
| 06:35 | which means, it returns True if the expression is False |
| 06:40 | and returns False if the expression is True. |
| 06:44 | The syntax of logical NOT operator is- |
| 06:48 | Exclamation mark space expression |
| 06:52 | or opening square bracket space exclamation mark space expression space closing square bracket. |
| 07:00 | Let us see an example. |
| 07:03 | I have already typed the code in a file. |
| 07:05 | So, I will go to the terminal and type: gedit space logicalNOT dot sh space ampersand sign press Enter. |
| 07:18 | Now, type the code as shown here in your logicalNOT dot sh file. |
| 07:24 | This is the shebang line as we already know. |
| 07:28 | $1 is the first command line argument passed to the script. |
| 07:33 | - (hyphen) f checks if the file exists with the same name that was passed as an argument. |
| 07:41 | So, it will return True if the file exists and False if it does not exist. |
| 07:48 | This NOT operator here, inverses the returned value. |
| 07:52 | Which means, if a file of that name exists, the condition will be True. |
| 07:58 | But the NOT operator will inverse its value to False. |
| 08:02 | And it will display the message FILE does not exist. |
| 08:07 | Here in the else statement, it displays the message FILE exists. |
| 08:13 | fi marks the end of if loop. |
| 08:16 | Now , switch to the terminal. |
| 08:18 | Let me clear the prompt. |
| 08:20 | Let's create an empty file with the name test.txt. |
| 08:25 | Type : touch space test dot txt press Enter. |
| 08:32 | Next, make the script executable by typing:
chmod space plus x space logicalNOT dot sh press Enter. |
| 08:45 | Now, type: dot slash logicalNOT dot sh space test dot txt press Enter. |
| 08:55 | Our shell script will check whether the file exists. |
| 09:00 | Our file test dot txt exists, hence the value will be true. |
| 09:07 | Then the logical NOT will inverse that value and return False. |
| 09:12 | Because the evaluation is False, the else statement is evaluated. |
| 09:18 | And the message displayed is -File 'test.txt' exists. |
| 09:23 | Try executing the program again with argument test1.txt. |
| 09:29 | And observe the control flow as explained before. |
| 09:33 | Come back to our slides. Let us summarize. |
| 09:37 | In this tutorial, we learnt the usage of:
|
| 09:45 | As an assignment, |
| 09:47 | check whether the file exists |
| 09:49 | and is executable |
| 09:51 | using logical operators explained in this tutorial. |
| 09:56 | (Hint: man space test)
|
| 09:59 | Watch the video available at the link shown below. |
| 10:02 | It summarizes the Spoken-Tutorial project. |
| 10:05 | If you do not have good bandwidth, you can download and watch it. |
| 10:09 | The Spoken Tutorial Project team: |
| 10:12 | Conducts workshops using spoken tutorials. |
| 10:15 | Gives certificates to those who pass an online test. |
| 10:19 | For more details, please write to contact@spoken-tutorial.org |
| 10:26 | Spoken Tutorial Project is a part of the Talk to a Teacher project. |
| 10:30 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 10:37 | More information on this mission is available at the link shown below. |
| 10:42 | The script has been contributed by FOSSEE and spoken-tutorial team. |
| 10:47 | This is Ashwini Patil from IIT Bombay, signing off. |
| 10:51 | Thank you for joining. |
Contributors and Content Editors
PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14, Yogananda.india
