Difference between revisions of "BASH/C2/Conditional-execution/English-timed"
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(Created page with "'''Title of script: Conditional Execution in BASH''' '''Author:''' Lavitha Pereira '''Keywords: video tutorial, Bash shell, Simple if, else-if.''' {| border=1 !Time !Narr...") |
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| − | | 02: 28 | + | | 02:28 |
| Let's take another expression; type: | | Let's take another expression; type: | ||
'''test space 4 space hyphen eq space 5 semicolon space echo space dollar sign question mark .''' | '''test space 4 space hyphen eq space 5 semicolon space echo space dollar sign question mark .''' | ||
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| − | | 02: 48 | + | | 02:48 |
| It returns '''one''' which means '''false''' . | | It returns '''one''' which means '''false''' . | ||
|- | |- | ||
| − | | 02: 52 | + | | 02:52 |
| i.e.'''4''' is not equal to '''5.''' | | i.e.'''4''' is not equal to '''5.''' | ||
|- | |- | ||
| − | | 02: 56 | + | | 02:56 |
| Now let's write the same expression within square brackets, type: | | Now let's write the same expression within square brackets, type: | ||
|- | |- | ||
| − | | 03: 01 | + | | 03:01 |
| '''opening square bracket''' space '''4''' space '''hyphen '''eq''' space '''5''' space '''closing square bracket semicolon''' space '''echo''' space '''dollar sign question mark''' Press '''Enter'''. | | '''opening square bracket''' space '''4''' space '''hyphen '''eq''' space '''5''' space '''closing square bracket semicolon''' space '''echo''' space '''dollar sign question mark''' Press '''Enter'''. | ||
|- | |- | ||
| − | | 03: 21 | + | | 03:21 |
| It also returns '''one''' which means '''false''' | | It also returns '''one''' which means '''false''' | ||
|- | |- | ||
| − | | 03: 25 | + | | 03:25 |
| i.e.''' 4''' is not equal to '''5''' | | i.e.''' 4''' is not equal to '''5''' | ||
|- | |- | ||
| − | | 03: 29 | + | | 03:29 |
| This can be extended for other kind of testing. | | This can be extended for other kind of testing. | ||
|- | |- | ||
| − | | 03: 33 | + | | 03:33 |
| Please type '''man space test''' and explore its usage. | | Please type '''man space test''' and explore its usage. | ||
|- | |- | ||
| − | | 03: 40 | + | | 03:40 |
| Now let us go back to our slides. | | Now let us go back to our slides. | ||
|- | |- | ||
| − | | 03: 43 | + | | 03:43 |
| Now we will see the syntax for '''if''' statement- | | Now we will see the syntax for '''if''' statement- | ||
|- | |- | ||
| − | | 03: 48 | + | | 03:48 |
| '''if space opening square bracket space expression space closing square bracket semicolon space then''' | | '''if space opening square bracket space expression space closing square bracket semicolon space then''' | ||
|- | |- | ||
| − | | 03: 59 | + | | 03:59 |
| On the next line,type '''commands''' or '''statements''' that you want to execute. | | On the next line,type '''commands''' or '''statements''' that you want to execute. | ||
|- | |- | ||
| − | | 04: 05 | + | | 04:05 |
| Lastly, end the '''if loop''' with '''fi.''' | | Lastly, end the '''if loop''' with '''fi.''' | ||
|- | |- | ||
| − | | 04: 11 | + | | 04:11 |
| The Basic rules of condition are: | | The Basic rules of condition are: | ||
|- | |- | ||
| − | | 04: 14 | + | | 04:14 |
| Always keep spaces between the brackets and the expression. | | Always keep spaces between the brackets and the expression. | ||
|- | |- | ||
| − | | 04: 19 | + | | 04:19 |
| Always terminate the line using '''semicolon''' before keyword “'''then”'''. | | Always terminate the line using '''semicolon''' before keyword “'''then”'''. | ||
|- | |- | ||
| − | | 04: 25 | + | | 04:25 |
| '''Semicolon''' is used to terminate the statement or an expression. | | '''Semicolon''' is used to terminate the statement or an expression. | ||
|- | |- | ||
| − | | 04: 31 | + | | 04:31 |
| It is recommended'' ''to quote string variables, if you use them in conditions. | | It is recommended'' ''to quote string variables, if you use them in conditions. | ||
|- | |- | ||
| − | | 04: 38 | + | | 04:38 |
| Don't forget to close the conditional block with “'''fi”.''' | | Don't forget to close the conditional block with “'''fi”.''' | ||
|- | |- | ||
| − | | 04: 43 | + | | 04:43 |
| Let us see an example on '''if statement.''' | | Let us see an example on '''if statement.''' | ||
|- | |- | ||
| − | | 04: 46 | + | | 04:46 |
| Come back to the '''terminal'''. | | Come back to the '''terminal'''. | ||
|- | |- | ||
| − | | 04: 49 | + | | 04:49 |
| I will open an already existing script file named '''simpleif.sh''' | | I will open an already existing script file named '''simpleif.sh''' | ||
|- | |- | ||
| − | | 04: 58 | + | | 04:58 |
| This Bash script displays the message “count is 100” when the '''count''' equals to 100 | | This Bash script displays the message “count is 100” when the '''count''' equals to 100 | ||
|- | |- | ||
| − | | 05: 06 | + | | 05:06 |
| This is first line of '''Bash shell''' script known as '''shebang line.''' | | This is first line of '''Bash shell''' script known as '''shebang line.''' | ||
|- | |- | ||
| − | | 05: 12 | + | | 05:12 |
| '''An integer 100''' is assigned to a '''variable count.''' | | '''An integer 100''' is assigned to a '''variable count.''' | ||
|- | |- | ||
| − | | 05: 17 | + | | 05:17 |
| Note that, there should not be any space between''' count, <nowiki>=</nowiki>''' and '''100.''' | | Note that, there should not be any space between''' count, <nowiki>=</nowiki>''' and '''100.''' | ||
|- | |- | ||
| − | | 05: 24 | + | | 05:24 |
| This expression checks whethe '''count''' is '''equal to hundred.''' | | This expression checks whethe '''count''' is '''equal to hundred.''' | ||
|- | |- | ||
| − | | 05: 30 | + | | 05:30 |
| Here ''' -eq ''' is '''comparison operator''' . | | Here ''' -eq ''' is '''comparison operator''' . | ||
|- | |- | ||
| − | | 05: 35 | + | | 05:35 |
| If the condition is true, it will display the message '''count is 100''' | | If the condition is true, it will display the message '''count is 100''' | ||
|- | |- | ||
| − | | 05: 41 | + | | 05:41 |
| '''fi''' is to end '''if''' block. | | '''fi''' is to end '''if''' block. | ||
|- | |- | ||
| − | | 05: 45 | + | | 05:45 |
| Save the file by pressing''' “Ctrl + s”''' | | Save the file by pressing''' “Ctrl + s”''' | ||
|- | |- | ||
| − | | 05: 49 | + | | 05:49 |
| Go back to the '''Terminal.''' | | Go back to the '''Terminal.''' | ||
|- | |- | ||
| − | | 05: 51 | + | | 05:51 |
| To make the file executable, type: '''chmod space plus x space simpleif.sh''' and Press '''Enter'''. | | To make the file executable, type: '''chmod space plus x space simpleif.sh''' and Press '''Enter'''. | ||
|- | |- | ||
| − | | 06: 04 | + | | 06:04 |
| Let me clear the prompt. | | Let me clear the prompt. | ||
|- | |- | ||
| − | | 06: 06 | + | | 06:06 |
| Now type dot slash '''simpleif.sh''' Press '''Enter'''. | | Now type dot slash '''simpleif.sh''' Press '''Enter'''. | ||
|- | |- | ||
| − | | 06: 14 | + | | 06:14 |
| Here it is displayed: | | Here it is displayed: | ||
|- | |- | ||
| − | | 06: 16 | + | | 06:16 |
| '''Count is 100.''' | | '''Count is 100.''' | ||
|- | |- | ||
| − | | 06: 18 | + | | 06:18 |
| Try changing the value of '''variable '''count ''' and execute the script. | | Try changing the value of '''variable '''count ''' and execute the script. | ||
|- | |- | ||
| − | | 06: 24 | + | | 06:24 |
| Switch back to slides. | | Switch back to slides. | ||
|- | |- | ||
| − | | 06: 26 | + | | 06:26 |
| We will see ''' if-else''' condition. | | We will see ''' if-else''' condition. | ||
|- | |- | ||
| − | | 06: 30 | + | | 06:30 |
| The general syntax is: '''if space opening square bracket space condition space closing square bracket space semicolon space then''' | | The general syntax is: '''if space opening square bracket space condition space closing square bracket space semicolon space then''' | ||
|- | |- | ||
| − | | 06: 44 | + | | 06:44 |
| On the next line, type '''commands''' | | On the next line, type '''commands''' | ||
|- | |- | ||
| − | | 06: 47 | + | | 06:47 |
| On the next line, there is '''else''' statement | | On the next line, there is '''else''' statement | ||
|- | |- | ||
| − | | 06: 51 | + | | 06:51 |
| And again type '''some other commands'''. | | And again type '''some other commands'''. | ||
|- | |- | ||
| − | | 06: 55 | + | | 06:55 |
| on the next line, type '''fi''' to end '''i ''' block. | | on the next line, type '''fi''' to end '''i ''' block. | ||
|- | |- | ||
| − | | 07: 00 | + | | 07:00 |
| Let us study the usage of '''if-else''' with an interesting password program. | | Let us study the usage of '''if-else''' with an interesting password program. | ||
|- | |- | ||
| − | | 07: 06 | + | | 07:06 |
| Come back to the terminal. | | Come back to the terminal. | ||
|- | |- | ||
| − | | 07: 09 | + | | 07:09 |
| I will open the file '''ifelse.sh''' | | I will open the file '''ifelse.sh''' | ||
|- | |- | ||
| − | | 07: 14 | + | | 07:14 |
| This is the '''shebang line''' | | This is the '''shebang line''' | ||
|- | |- | ||
| − | | 07: 17 | + | | 07:17 |
| Here,'''abc123''' is stored in the variable '''PASS''' | | Here,'''abc123''' is stored in the variable '''PASS''' | ||
|- | |- | ||
| − | | 07: 23 | + | | 07:23 |
| As '''abc123''' is a string, it should be written within '''double-quotes.''' | | As '''abc123''' is a string, it should be written within '''double-quotes.''' | ||
|- | |- | ||
| − | | 07: 29 | + | | 07:29 |
| The '''read command''' reads '''one line''' of data from the '''standard input.''' | | The '''read command''' reads '''one line''' of data from the '''standard input.''' | ||
|- | |- | ||
| − | | 07: 35 | + | | 07:35 |
| In this case, standard input is our keyboard'''.''' | | In this case, standard input is our keyboard'''.''' | ||
|- | |- | ||
| − | | 07: 39 | + | | 07:39 |
| Hyphen '''s''' is for silent mode. | | Hyphen '''s''' is for silent mode. | ||
|- | |- | ||
| − | | 07: 43 | + | | 07:43 |
| Which means the entered password will not be displayed as we type. | | Which means the entered password will not be displayed as we type. | ||
|- | |- | ||
| − | | 07: 48 | + | | 07:48 |
| We don't want others to see our password. | | We don't want others to see our password. | ||
|- | |- | ||
| − | | 07: 52 | + | | 07:52 |
| Hyphen '''p''' is for prompt. | | Hyphen '''p''' is for prompt. | ||
|- | |- | ||
| − | | 07: 55 | + | | 07:55 |
| It will display a string “'Enter password: ” before it takes input from user. | | It will display a string “'Enter password: ” before it takes input from user. | ||
|- | |- | ||
| − | | 08: 01 | + | | 08:01 |
| '''mypassword''' is a ''' variable.''' | | '''mypassword''' is a ''' variable.''' | ||
|- | |- | ||
| − | | 08: 04 | + | | 08:04 |
| It stores the '''string,''' in this case the '''password''' entered by the user. | | It stores the '''string,''' in this case the '''password''' entered by the user. | ||
|- | |- | ||
| − | | 08: 10 | + | | 08:10 |
| This checks that the entered password matches the value of the variable '''PASS.''' | | This checks that the entered password matches the value of the variable '''PASS.''' | ||
|- | |- | ||
| − | | 08: 17 | + | | 08:17 |
| It is stored in a variable''' mypassword''' | | It is stored in a variable''' mypassword''' | ||
|- | |- | ||
| − | | 08: 21 | + | | 08:21 |
| If the password matches, it will display the'' ''message | | If the password matches, it will display the'' ''message | ||
|- | |- | ||
| − | | 08: 25 | + | | 08:25 |
| '''“Password accepted”''' | | '''“Password accepted”''' | ||
|- | |- | ||
| − | | 08: 27 | + | | 08:27 |
| else it will display | | else it will display | ||
| Line 392: | Line 392: | ||
|- | |- | ||
| − | | 08: 31 | + | | 08:31 |
| '''fi '''is the end of '''if-else loop''' | | '''fi '''is the end of '''if-else loop''' | ||
|- | |- | ||
| − | | 08: 34 | + | | 08:34 |
| Now save the file by pressing “'''Ctrl s”''' . | | Now save the file by pressing “'''Ctrl s”''' . | ||
|- | |- | ||
| − | | 08: 38 | + | | 08:38 |
| Come back to our '''terminal''', make the file executable type: | | Come back to our '''terminal''', make the file executable type: | ||
| Line 406: | Line 406: | ||
|- | |- | ||
| − | | 08: 52 | + | | 08:52 |
| Type '''dot slash ifelse.sh .''' Press ''' Enter.''' | | Type '''dot slash ifelse.sh .''' Press ''' Enter.''' | ||
|- | |- | ||
| − | | 08: 57 | + | | 08:57 |
| Here it is displayed : | | Here it is displayed : | ||
|- | |- | ||
| − | | 08: 59 | + | | 08:59 |
| Enter''' password''': | | Enter''' password''': | ||
Revision as of 11:13, 9 December 2014
Title of script: Conditional Execution in BASH
Author: Lavitha Pereira
Keywords: video tutorial, Bash shell, Simple if, else-if.
| Time | Narration |
|---|---|
| 00:01 | Dear friends, Welcome to the spoken tutorial on Conditional execution in Bash. |
| 00:08 | In this tutorial, we will learn |
| 00:10 | * Use of test command |
| 00:13 | and Conditional Statements |
| 00:15 | We will do this using a few examples. |
| 00:19 | To follow this tutorial, |
| 00:21 | You should be familiar with GNU/Linux Operating System. |
| 00:26 | If not, for relevant tutorials please visit our website which is are shown. |
| 00:32 | For this tutorial I am using |
| 00:35 | * Ubuntu Linux 12.04 OS |
| 00:39 | and * GNU Bash version 4.1.10 |
| 00:43 | GNU Bash version 4 or above is recommended for practice . |
| 00:49 | Let us start with an introduction to test. |
| 00:52 | * test is a built-in command, which returns the exit status. |
| 00:57 | * It returns 0 Zero for True and 1 One for False. |
| 01:02 | * Return value depends on the evaluation of the expression. |
| 01:07 | * One can get the return status by typing Dollar and question mark sign ($?) |
| 01:14 | * An expression can be evaluated in two ways- |
| 01:18 | # One by using the keyword test |
| 01:21 | And Other by using the expression enclosed within square brackets. |
| 01:27 | Now open the terminal by pressing Ctrl+Alt and T keys simultaneously. |
| 01:35 | Type: test space 4 space hyphen eq space 4 semicolon space echo space dollar sign and a question mark. Press Enter |
| 01:53 | It returns zero which means true
|
| 01:57 | 4 is equals to 4 |
| 02:00 | Next type: |
| 02:02 | opening square bracket space 4 space hyphen eq space 4 space closing square bracket semicolon space echo space dollar sign and a question mark. Press Enter. |
| 02:22 | It returns zero which means true |
| 02:25 | i.e.4 is equal to 4. |
| 02:28 | Let's take another expression; type:
test space 4 space hyphen eq space 5 semicolon space echo space dollar sign question mark . Press Enter |
| 02:48 | It returns one which means false . |
| 02:52 | i.e.4 is not equal to 5. |
| 02:56 | Now let's write the same expression within square brackets, type: |
| 03:01 | opening square bracket space 4 space hyphen eq space 5 space closing square bracket semicolon space echo space dollar sign question mark Press Enter. |
| 03:21 | It also returns one which means false |
| 03:25 | i.e. 4 is not equal to 5 |
| 03:29 | This can be extended for other kind of testing. |
| 03:33 | Please type man space test and explore its usage. |
| 03:40 | Now let us go back to our slides. |
| 03:43 | Now we will see the syntax for if statement- |
| 03:48 | if space opening square bracket space expression space closing square bracket semicolon space then |
| 03:59 | On the next line,type commands or statements that you want to execute. |
| 04:05 | Lastly, end the if loop with fi. |
| 04:11 | The Basic rules of condition are: |
| 04:14 | Always keep spaces between the brackets and the expression. |
| 04:19 | Always terminate the line using semicolon before keyword “then”. |
| 04:25 | Semicolon is used to terminate the statement or an expression. |
| 04:31 | It is recommended to quote string variables, if you use them in conditions. |
| 04:38 | Don't forget to close the conditional block with “fi”. |
| 04:43 | Let us see an example on if statement. |
| 04:46 | Come back to the terminal. |
| 04:49 | I will open an already existing script file named simpleif.sh |
| 04:58 | This Bash script displays the message “count is 100” when the count equals to 100 |
| 05:06 | This is first line of Bash shell script known as shebang line. |
| 05:12 | An integer 100 is assigned to a variable count. |
| 05:17 | Note that, there should not be any space between count, = and 100. |
| 05:24 | This expression checks whethe count is equal to hundred. |
| 05:30 | Here -eq is comparison operator . |
| 05:35 | If the condition is true, it will display the message count is 100 |
| 05:41 | fi is to end if block. |
| 05:45 | Save the file by pressing “Ctrl + s”
|
| 05:49 | Go back to the Terminal. |
| 05:51 | To make the file executable, type: chmod space plus x space simpleif.sh and Press Enter. |
| 06:04 | Let me clear the prompt. |
| 06:06 | Now type dot slash simpleif.sh Press Enter. |
| 06:14 | Here it is displayed: |
| 06:16 | Count is 100. |
| 06:18 | Try changing the value of variable count and execute the script. |
| 06:24 | Switch back to slides. |
| 06:26 | We will see if-else condition. |
| 06:30 | The general syntax is: if space opening square bracket space condition space closing square bracket space semicolon space then |
| 06:44 | On the next line, type commands |
| 06:47 | On the next line, there is else statement |
| 06:51 | And again type some other commands. |
| 06:55 | on the next line, type fi to end i block. |
| 07:00 | Let us study the usage of if-else with an interesting password program. |
| 07:06 | Come back to the terminal. |
| 07:09 | I will open the file ifelse.sh |
| 07:14 | This is the shebang line |
| 07:17 | Here,abc123 is stored in the variable PASS |
| 07:23 | As abc123 is a string, it should be written within double-quotes. |
| 07:29 | The read command reads one line of data from the standard input. |
| 07:35 | In this case, standard input is our keyboard. |
| 07:39 | Hyphen s is for silent mode. |
| 07:43 | Which means the entered password will not be displayed as we type. |
| 07:48 | We don't want others to see our password. |
| 07:52 | Hyphen p is for prompt. |
| 07:55 | It will display a string “'Enter password: ” before it takes input from user. |
| 08:01 | mypassword is a variable. |
| 08:04 | It stores the string, in this case the password entered by the user. |
| 08:10 | This checks that the entered password matches the value of the variable PASS. |
| 08:17 | It is stored in a variable mypassword |
| 08:21 | If the password matches, it will display the message |
| 08:25 | “Password accepted” |
| 08:27 | else it will display
“Access denied” |
| 08:31 | fi is the end of if-else loop |
| 08:34 | Now save the file by pressing “Ctrl s” . |
| 08:38 | Come back to our terminal, make the file executable type:
chmod space plus x space ifelse.sh .Press Enter. |
| 08:52 | Type dot slash ifelse.sh . Press Enter.
|
| 08:57 | Here it is displayed : |
| 08:59 | Enter password: |
| 09:00 | I will type abc press Enter |
| 09:05 | As the password entered is wrong, it displays the message as “Access denied” |
| 09:11 | Let's execute again, but this time we will enter password as abc123 |
| 09:21 | It is displayed as:
Password accepted |
| 09:25 | This bring us to the end of this tutorial. |
| 09:28 | Come back to our slides and summarize. |
| 09:31 | In this tutorial we have covered Usage of test command , Simple if statement & if else statement . |
| 09:41 | As an assignment
|
| 09:43 | # Write a script , take your name as an input. |
| 09:46 | # It should check this name with your system's username. |
| 09:51 | If the username matches, it should greet you by displaying “Hello” |
| 09:56 | # Else, it should display “Try again” |
| 10:00 | HINT: Your system's username is stored in a variable $USER |
| 10:06 | Watch the video available at the link shown below |
| 10:09 | It summarizes the Spoken Tutorial project |
| 10:11 | If you do not have good bandwidth, you can download and watch it |
| 10:16 | The Spoken Tutorial Project Team |
| 10:18 | Conducts workshops using spoken tutorials |
| 10:22 | Gives certificates to those who pass an online test |
| 10:26 | For more details, please write to contact@spoken-tutorial.org |
| 10:33 | Spoken Tutorial Project is a part of the Talk to a Teacher project |
| 10:37 | It is supported by the National Mission on Education through ICT, MHRD, Government of India |
| 10:45 | More information on this Mission is available at the link shown below. |
| 10:51 | The script has been contributed by FOSSEE and spoken-tutorial team. |
| 10:56 | This is Ashwini from IIT Bombay signning off. |
| 11:01 | Thank you for joining. |
