BASH/C2/Conditional-execution/English-timed - Revision history

Pratik kamble at 10:23, 23 March 2017

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Pratik kamble at 11:08, 20 February 2017

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Pratik kamble at 11:05, 20 February 2017

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Sandhya.np14 at 09:44, 10 July 2015

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Sandhya.np14 at 09:06, 10 July 2015

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Sandhya.np14 at 05:42, 3 July 2015

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PoojaMoolya at 11:48, 6 April 2015

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PoojaMoolya at 11:44, 17 December 2014

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Ranjana at 05:43, 9 December 2014

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Ranjana: 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..."

2014-11-24T10:15:49Z

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..."

New page

'''Title of script: Conditional Execution in BASH'''

'''Author:''' Lavitha Pereira

'''Keywords: video tutorial, Bash shell, Simple if, else-if.'''

{| border=1
!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, <nowiki>=</nowiki>''' 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.

|}

@@ Line 403: / Line 403: @@
 |-
 | 08:59
-| '''Enter password''':
+| '''Enter password''': I will type '''abc'''. Press '''Enter'''.
-−
-|-
-| 09:00
-| I will type '''abc'''. Press '''Enter'''.
 |-

@@ Line 391: / Line 391: @@
 |-
 |  08:38
-| Come back to our '''terminal''', make the file executable. Type:
+| Come back to our '''terminal''', make the file executable. Type:'''chmod''' space '''plus x''' space '''ifelse.sh'''. Press '''Enter.'''
 '''chmod''' space '''plus x''' space '''ifelse.sh'''. Press '''Enter.'''
 |-

@@ Line 1: / Line 1: @@
 {| border=1
-!Time
+|'''Time'''
-!Narration
+|'''Narration'''
 |-
@@ Line 19: / Line 13: @@
 |-
 |  00:10
-|* Use of '''test''' command and
+| Use of '''test''' command and
 |-
 |  00:13
-|* '''Conditional''' statements.
+| '''Conditional''' statements.
 |-
@@ Line 47: / Line 41: @@
 |-
 |  00:35
-|* '''Ubuntu Linux 12.04 ''' OS and
+| '''Ubuntu Linux 12.04 ''' OS and
 |-
 |  00:39
-|* '''GNU Bash''' version '''4.1.10'''
+| '''GNU Bash''' version '''4.1.10'''
 |-
@@ Line 185: / Line 179: @@
 |-
 | 04:14
-|* Always keep spaces between the brackets and the expression.
+| Always keep spaces between the brackets and the expression.
 |-
 | 04:19
-|* Always terminate the line using semicolon before keyword “'''then”'''.
+| Always terminate the line using semicolon before keyword “'''then”'''.
 |-
 | 04:25
-|* Semicolon is used to terminate the statement or an expression.
+| Semicolon is used to terminate the statement or an expression.
 |-
@@ Line 482: / Line 476: @@
 |-
 | 10:18
-|* Conducts workshops using spoken tutorials.
+| Conducts workshops using spoken tutorials.
 |-
 | 10:22
-|* Gives certificates to those who pass an online test.
+| Gives certificates to those who pass an online test.
 |-

@@ Line 39: / Line 39: @@
 |-
 |  00:26
-| If not, for relevant tutorials please visit our website which is as shown.
+| If not, for relevant tutorials, please visit our website which is as shown.
 |-
@@ Line 67: / Line 67: @@
 |-
 |  00:57
-| It returns '''0''' (zero) for '''True''' and '''1''' (one) for '''False'''.
+| It returns 0 (zero) for '''True''' and '''1''' (one) for '''False'''.
 |-
 |   01:02
-| '''Return '''value''' depends on the evaluation of the expression.
+| '''Return''' value depends on the evaluation of the expression.
 |-
 | 01:07
-| One can get the '''return''' status by typing '''Dollar and question mark sign ($?)'''.
+| One can get the '''return''' status by typing Dollar and question mark sign ($?).
 |-
@@ Line 83: / Line 83: @@
 |-
 | 01:18
-| One, by using the keyword ''' test'''.
+| One- by using the keyword ''' test'''.
 |-
 | 01:21
-| And other, by using the expression enclosed within square brackets.
+| And other by using the expression enclosed within square brackets.
 |-
@@ Line 99: / Line 99: @@
 |-
 |  01:53
-| It returns  zero  which means ''' true'''.
+| It returns  zero  which means ''' True'''.
 |-
@@ Line 111: / Line 111: @@
 |-
 | 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'''.
+| '''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'''.
+|  It returns zero which means ''' True'''.
 |-
@@ Line 123: / Line 123: @@
 |-
 | 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.
 Press''' Enter'''.
 |-
 | 02:48
-| It returns one which means '''false'''.
+| It returns one which means '''False'''.
 |-
@@ Line 141: / Line 141: @@
 |-
 | 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 and a question mark. Press '''Enter'''.
 |-
 | 03:21
-| It also returns one which means '''false'''.
+| It also returns one which means '''False'''.
 |-
@@ Line 161: / Line 161: @@
 |-
 | 03:40
-| Now let us go back to our '''slides'''.
+| Now, let us go back to our '''slides'''.
 |-
@@ Line 173: / Line 173: @@
 |-
 | 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
-| Lastly, end the '''if loop''' with '''fi.'''
+| Lastly, end the '''if''' loop with '''fi.'''
 |-
@@ Line 402: / Line 402: @@
 |-
 | 08:52
-| Type '''dot slash ifelse.sh .''' Press ''' Enter.'''
+| Type: '''dot slash ifelse.sh .''' Press ''' Enter.'''
-−
 |-

@@ Line 305: / Line 305: @@
 |-
 | 06:55
-| on the next line, type '''fi''' to end '''i ''' block.
+| on the next line, type '''fi''' to end '''if''' block.
 |-

@@ Line 59: / Line 59: @@
 |-
 |   00:49
-|   Let us start with an introduction to '''test.'''
+|Let us start with an introduction to '''test.'''
 |-
@@ Line 100: / Line 100: @@
 |  01:53
 | It returns ''' zero ''' which means ''' true'''
 |-
@@ Line 251: / Line 250: @@
 | 05:45
 | Save the file by pressing''' “Ctrl + s”'''
 |-
@@ Line 387: / Line 385: @@
 |-
 | 08:27
-| else it will display
+| else it will display '''“Access denied”'''
-−
 '''“Access denied”'''
 |-
@@ Line 432: / Line 428: @@
 |-
 | 09:21
-| It is displayed as:
+| It is displayed as: '''Password accepted'''
 '''Password accepted'''
 |-
@@ Line 450: / Line 445: @@
 |  09:41
 |  As an assignment
 |-