Difference between revisions of "BASH/C2/Logical-Operators/English-timed"
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| 06:25 | | 06:25 | ||
| − | | Let's switch back to our slides. | + | | Let's switch back to our '''slides'''. |
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| 06:31 | | 06:31 | ||
| − | | | + | | It inverts the '''boolean''' value of an expression |
|- | |- | ||
| 06:35 | | 06:35 | ||
| − | | | + | | which means, it returns '''True''' if the expression is '''False''' |
|- | |- | ||
| 06:40 | | 06:40 | ||
| − | | | + | | and returns '''False''' if the expression is '''True'''. |
|- | |- | ||
| 06:44 | | 06:44 | ||
| − | | The syntax of '''logical NOT''' operator is | + | | The syntax of '''logical NOT''' operator is- |
|- | |- | ||
| 06:48 | | 06:48 | ||
| − | | | + | | '''Exclamation mark''' space '''expression''' |
|- | |- | ||
| 06:52 | | 06:52 | ||
| − | | Or ''' | + | | Or '''opening square bracket space exclamation mark space expression space closing square bracket'''. |
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| 07:03 | | 07:03 | ||
| − | | I have already typed the code in a file. | + | | I have already typed the '''code''' in a file. |
|- | |- | ||
| 07:05 | | 07:05 | ||
| − | | So, I will go to the '''terminal ''' and type '''gedit space logicalNOT dot sh space ampersand | + | | So, I will go to the '''terminal ''' and type: '''gedit space logicalNOT dot sh space ampersand''' sign press ''' Enter.''' |
|- | |- | ||
| 07:18 | | 07:18 | ||
| − | | Now type the code as shown here in your '''logicalNOT dot sh''' file. | + | | Now, type the code as shown here in your '''logicalNOT dot sh''' file. |
|- | |- | ||
| 07:24 | | 07:24 | ||
| − | | This is the ''' shebang line | + | | This is the ''' shebang line '''as we already know. |
|- | |- | ||
| 07:28 | | 07:28 | ||
| − | | '''$1''' is the first '''command line argument''' passed to the script. | + | | '''$1''' is the first '''command line argument''' passed to the '''script'''. |
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| 07:41 | | 07:41 | ||
| − | | So, it will return ''' | + | | So, it will return '''True''' if the file exists and '''False''' if it does not exist. |
|- | |- | ||
| 07:48 | | 07:48 | ||
| − | | This '''NOT operator''' here inverses the returned value. | + | | This '''NOT operator''' here, inverses the returned value. |
|- | |- | ||
| 07:52 | | 07:52 | ||
| − | | Which means, if a file of that name exists, the | + | | Which means, if a file of that name exists, the condition will be '''True.''' |
|- | |- | ||
| 07:58 | | 07:58 | ||
| − | | But the '''NOT operator''' will inverse its value to ''' | + | | But the '''NOT operator''' will inverse its value to '''False'''. |
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| 08:18 | | 08:18 | ||
| − | | Let me clear the prompt. | + | | Let me clear the '''prompt'''. |
|- | |- | ||
| 08:20 | | 08:20 | ||
| − | | Let's create an empty file with the name '''test.txt''' | + | | Let's create an empty file with the name '''test.txt'''. |
|- | |- | ||
| 08:25 | | 08:25 | ||
| − | | Type : '''touch space test dot txt''' | + | | Type : '''touch space test dot txt''' press '''Enter.''' |
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| 08:45 | | 08:45 | ||
| − | | Now type '''dot slash logicalNOT dot sh space test dot txt''' press ''' Enter.''' | + | | Now, type: '''dot slash logicalNOT dot sh space test dot txt''' press ''' Enter.''' |
|- | |- | ||
| 08:55 | | 08:55 | ||
| − | | Our shell script will check whether the file exists. | + | | Our '''shell script''' will check whether the file exists. |
|- | |- | ||
| 09:00 | | 09:00 | ||
| − | | Our file '''test dot txt ''' exists hence the value will be ''' true.''' | + | | Our file '''test dot txt ''' exists, hence the value will be ''' true.''' |
|- | |- | ||
| 09:07 | | 09:07 | ||
| − | | Then the '''logical NOT''' will inverse that value and return ''' | + | | Then the '''logical NOT''' will inverse that value and return '''False.''' |
|- | |- | ||
| 09:12 | | 09:12 | ||
| − | | Because the evaluation is ''' | + | | Because the evaluation is '''False''', the '''else statement''' is evaluated. |
|- | |- | ||
| 09:18 | | 09:18 | ||
| − | | And the message displayed is -'''File 'test.txt' exists''' | + | | And the message displayed is -'''File 'test.txt' exists'''. |
|- | |- | ||
| 09:23 | | 09:23 | ||
| − | | Try executing the program again with argument '''test1.txt''' | + | | Try executing the program again with '''argument''' '''test1.txt'''. |
|- | |- | ||
| 09:29 | | 09:29 | ||
| − | | And observe the control flow | + | | And observe the control flow as explained before. |
|- | |- | ||
| 09:33 | | 09:33 | ||
| − | | Come back to our slides. Let us summarize. | + | | Come back to our '''slides'''. Let us summarize. |
|- | |- | ||
| 09:37 | | 09:37 | ||
| − | | In this tutorial we learnt the usage of | + | | In this tutorial, we learnt the usage of: |
* '''logical AND''' | * '''logical AND''' | ||
* '''logical OR '''and | * '''logical OR '''and | ||
| − | * '''logical NOT''' | + | * '''logical NOT'''. |
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| 09:51 | | 09:51 | ||
| − | | | + | | using '''logical operators ''' explained in this tutorial. |
|- | |- | ||
| 09:56 | | 09:56 | ||
| − | | | + | | (Hint: '''man space test''') |
|- | |- | ||
| 09:59 | | 09:59 | ||
| − | | Watch the video available at the link shown below | + | | Watch the video available at the link shown below. |
|- | |- | ||
| 10:02 | | 10:02 | ||
| − | | It summarizes the Spoken Tutorial project | + | | It summarizes the Spoken-Tutorial project. |
|- | |- | ||
| 10:05 | | 10:05 | ||
| − | | If you do not have good bandwidth, you can download and watch it | + | | If you do not have good bandwidth, you can download and watch it. |
|- | |- | ||
| 10:09 | | 10:09 | ||
| − | | The Spoken Tutorial Project | + | | The Spoken Tutorial Project team: |
|- | |- | ||
| 10:12 | | 10:12 | ||
| − | | Conducts workshops using spoken tutorials | + | | Conducts workshops using spoken tutorials. |
|- | |- | ||
| 10:15 | | 10:15 | ||
| − | | Gives certificates to those who pass an online test | + | | Gives certificates to those who pass an online test. |
|- | |- | ||
| Line 478: | Line 478: | ||
|- | |- | ||
| 10:26 | | 10:26 | ||
| − | | Spoken Tutorial Project is a part of the Talk to a Teacher project | + | | '''Spoken Tutorial''' Project is a part of the '''Talk to a Teacher''' project. |
|- | |- | ||
| 10:30 | | 10:30 | ||
| − | | It is supported by the National Mission on Education through ICT, MHRD, Government of India | + | | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
|- | |- | ||
| 10:37 | | 10:37 | ||
| − | | More information on this | + | | More information on this mission is available at the link shown below. |
|- | |- | ||
| Line 494: | Line 494: | ||
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| 10:47 | | 10:47 | ||
| − | | This is Ashwini Patil from IIT Bombay | + | | This is Ashwini Patil from IIT Bombay, signing off. |
|- | |- | ||
Revision as of 14:54, 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 |
| 00:10 | * Use of Logical AND
|
| 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 helps 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 an t keys simultaneousely on your keyboard. |
| 03:04 | Type: gedit space logical.sh space & 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 display 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
