Difference between revisions of "BASH/C2/Conditional-execution/English-timed"

From Script | Spoken-Tutorial
Jump to: navigation, search
(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...")
 
 
(8 intermediate revisions by 4 users not shown)
Line 1: Line 1:
'''Title of script: Conditional Execution in BASH'''
 
 
'''Author:''' Lavitha Pereira
 
 
'''Keywords: video tutorial, Bash shell, Simple if, else-if.'''
 
 
 
{| border=1  
 
{| border=1  
!Time  
+
|'''Time'''
!Narration  
+
|'''Narration'''
  
 
|-
 
|-
 
|  00:01
 
|  00:01
| Dear friends, Welcome to the spoken tutorial on '''Conditional execution in Bash.'''
+
| Dear friends, welcome to the '''spoken tutorial''' on '''Conditional execution''' in '''Bash.'''
  
 
|-
 
|-
 
|  00:08
 
|  00:08
|  In this tutorial, we will learn
+
|  In this tutorial, we will learn:
  
 
|-
 
|-
 
|  00:10
 
|  00:10
| * Use of '''test''' command
+
| Use of '''test''' command and
  
 
|-
 
|-
 
|  00:13
 
|  00:13
| and '''Conditional''' Statements
+
| '''Conditional''' statements.
  
 
|-
 
|-
Line 39: Line 33:
 
|-
 
|-
 
|  00:26
 
|  00:26
| If not, for relevant tutorials please visit our website which is are shown.
+
| If not, for relevant tutorials, please visit our website which is as shown.
  
 
|-
 
|-
 
|  00:32
 
|  00:32
|  For this tutorial I am using  
+
|  For this tutorial, I am using:
  
 
|-
 
|-
 
|  00:35
 
|  00:35
| * '''Ubuntu Linux 12.04 ''' OS  
+
| '''Ubuntu Linux 12.04 ''' OS and
  
 
|-
 
|-
 
|  00:39
 
|  00:39
| and * '''GNU Bash''' version '''4.1.10'''
+
| '''GNU Bash''' version '''4.1.10'''
  
 
|-
 
|-
 
|  00:43
 
|  00:43
| '''GNU Bash '''version '''4''' or above is recommended for practice .
+
| '''GNU Bash '''version 4 or above is recommended for practice.
  
 
|-
 
|-
 
|  00:49
 
|  00:49
|   Let us start with an introduction to '''test.'''
+
|Let us start with an introduction to '''test.'''
  
 
|-
 
|-
 
|  00:52
 
|  00:52
| * '''test''' is a '''built-in''' command, which returns the '''exit status.'''
+
| '''test''' is a '''built-in''' command which returns the '''exit status.'''
  
 
|-
 
|-
 
|  00:57
 
|  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
 
|  01:02
| '''Return '''value''' depends on the evaluation of the expression.
+
| '''Return''' value depends on the evaluation of the expression.
  
 
|-
 
|-
 
| 01:07
 
| 01:07
| * One can get the '''return''' status by typing '''Dollar and question mark sign ($?)'''
+
| One can get the '''return''' status by typing Dollar and question mark sign ($?).
  
 
|-
 
|-
 
| 01:14
 
| 01:14
| * An expression can be evaluated in two ways-
+
| An expression can be evaluated in two ways-
  
 
|-
 
|-
 
| 01:18
 
| 01:18
| # One by using the keyword ''' test'''
+
| One- by using the keyword ''' test'''.
  
 
|-
 
|-
 
| 01:21
 
| 01:21
| And Other by using the expression enclosed within square brackets.
+
| And other by using the expression enclosed within square brackets.
  
 
|-
 
|-
 
|  01:27
 
|  01:27
|  Now open the '''terminal''' by pressing '''Ctrl+Alt and '''T''' keys simultaneously.
+
|  Now, open the '''terminal''' by pressing '''Ctrl+Alt''' and '''T''' keys simultaneously.
  
 
|-
 
|-
 
|  01:35
 
|  01:35
| Type: '''test space 4 space hyphen eq space 4 semicolon space echo space dollar sign and a question mark. Press ''' Enter'''
+
| Type: '''test space 4 space hyphen eq space 4 semicolon space echo space dollar sign''' and a question mark. Press ''' Enter'''.
  
 
|-
 
|-
 
|  01:53
 
|  01:53
| It returns ''' zero ''' which means ''' true'''  
+
| It returns zero which means ''' True'''.
 
+
  
 
|-
 
|-
 
|  01:57
 
|  01:57
| '''4''' is equals to '''4'''
+
| '''4''' is equal to '''4'''.
  
 
|-
 
|-
 
|  02:00
 
|  02:00
| Next type:
+
| Next, type:
  
 
|-
 
|-
 
| 02:02
 
| 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
 
| 02:22
|  It returns '''zero''' which means ''' true'''  
+
|  It returns zero which means ''' True'''.
  
 
|-
 
|-
Line 123: Line 116:
  
 
|-
 
|-
| 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.
Press''' Enter'''
+
Press''' Enter'''.
  
 
|-
 
|-
| 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 and a 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 '''condition'''.
  
 
|-
 
|-
|  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 our '''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 the 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 whether '''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”'''
+
| Now '''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.  
+
Now switch back to our '''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 '''if''' 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 displays the message:
  
 
|-
 
|-
| 08: 25
+
| 08:25
 
| '''“Password accepted”'''
 
| '''“Password accepted”'''
  
 
|-
 
|-
| 08: 27
+
| 08:27
| else it will display
+
| else it will display '''“Access denied”'''.
 
+
'''“Access denied”'''
+
  
 
|-
 
|-
| 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:'''chmod''' space '''plus x''' space '''ifelse.sh'''. Press '''Enter.'''
 
+
'''chmod''' space '''plus x''' space '''ifelse.sh''' .Press '''Enter.'''
+
  
 
|-
 
|-
| 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''': I will type '''abc'''. Press '''Enter'''.
 
+
|-
+
| 09:00
+
| I will type '''abc''' press '''Enter'''
+
  
 
|-
 
|-
 
| 09:05
 
| 09:05
| As the password entered is wrong, it displays the message as ''' “Access denied”'''
+
| As the password entered is wrong, it displays the message as ''' “Access denied”'''.
  
 
|-
 
|-
 
| 09:11
 
| 09:11
| Let's execute again, but this time we will enter password as '''abc123'''
+
| Let's execute again but this time we will enter password as '''abc123'''.
  
 
|-
 
|-
 
| 09:21
 
| 09:21
| It is displayed as:
+
| It is displayed as: '''Password accepted'''.
'''Password accepted'''
+
  
 
|-
 
|-
 
|  09:25   
 
|  09:25   
| This bring us to the end of this tutorial.
+
| This brings us to the end of this tutorial.
  
 
|-
 
|-
 
|  09:28   
 
|  09:28   
| Come back to our slides and summarize.
+
| Come back to our '''slides''' and summarize.
  
 
|-
 
|-
 
|  09:31  
 
|  09:31  
| In this tutorial we have covered Usage of test command , Simple ''' if''' statement & '''if else '''statement .
+
| In this tutorial, we have covered usage of '''test''' command, simple '''if''' statement and '''if-else '''statement.
  
 
|-
 
|-
 
|  09:41  
 
|  09:41  
|  As an assignment
+
|  As an assignment-
 
+
  
 
|-
 
|-
 
|  09:43
 
|  09:43
| # Write a script , take your name as an input.
+
| Write a script, take your name as an input.
  
 
|-
 
|-
 
|  09:46
 
|  09:46
| # It should check this name with your system's username.
+
| It should check this name with your system's username.
  
 
|-
 
|-
 
| 09:51
 
| 09:51
| If the username matches, it should greet you by displaying “'''Hello'''”
+
| If the username matches, it should greet you by displaying “'''Hello'''”.
  
 
|-
 
|-
 
|  09:56
 
|  09:56
| # Else, it should display “'''Try again'''”
+
| Else, it should display “'''Try again'''”.
  
 
|-
 
|-
 
|  10:00
 
|  10:00
| HINT: Your system's username is stored in a variable '''$USER'''
+
| HINT: Your system's username is stored in a variable '''$USER'''.
  
 
|-
 
|-
 
| 10:06
 
| 10:06
| Watch the video available at the link shown below
+
| Watch the video available at the link shown below.
  
 
|-
 
|-
 
| 10:09
 
| 10:09
| It summarizes the Spoken Tutorial project  
+
| It summarizes the Spoken Tutorial project.
  
 
|-
 
|-
 
| 10:11
 
| 10:11
| 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.
  
 
|-
 
|-
 
| 10:16
 
| 10:16
|  The Spoken Tutorial Project Team
+
|  The Spoken Tutorial Project team:
  
 
|-
 
|-
 
| 10:18
 
| 10:18
| Conducts workshops using spoken tutorials  
+
| Conducts workshops using spoken tutorials.
  
 
|-
 
|-
 
| 10:22
 
| 10:22
| Gives certificates to those who pass an online test  
+
| Gives certificates to those who pass an online test.
  
 
|-
 
|-
Line 502: Line 483:
 
|-
 
|-
 
| 10:33
 
| 10:33
| 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.
  
 
|-
 
|-
 
| 10:37
 
| 10:37
| 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.
  
 
|-
 
|-
 
| 10:45
 
| 10:45
| More information on this Mission is available at the link shown below.
+
| More information on this mission is available at the link shown below.
  
 
|-
 
|-
Line 518: Line 499:
 
|-
 
|-
 
| 10:56
 
| 10:56
| This is Ashwini from IIT Bombay signning off.
+
| This is Ashwini from IIT Bombay, signing off.
  
 
|-
 
|-

Latest revision as of 15:53, 23 March 2017

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 and
00:13 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 as shown.
00:32 For this tutorial, I am using:
00:35 Ubuntu Linux 12.04 OS and
00:39 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 equal 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 and a 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 condition.
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 our 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 the 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 whether 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 Now 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 Now switch back to our 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 if 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 displays 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: 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 brings 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 and 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, signing off.
11:01 Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14