Difference between revisions of "BASH/C2/Case-statement/English-timed"

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| To follow this tutorial, you should have knowledge on basics of '''Shell Scripting'''.
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| To follow this tutorial, you should have knowledge on basics of '''Shell''' scripting.
  
 
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|  The '''Bash''' '''shell''' has two forms of '''conditional statements'''. '''if statement''' and '''case statement.'''
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|  The '''Bash''' '''shell''' has two forms of '''conditional statements'''-''' 'if' statement''' and''' 'case' statement.'''
  
 
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|'''Case statement '''can be alternately used in place of '''if-else statement'''.
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|'''Case''' statement can be alternately used in place of '''if-else''' statement.
  
 
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|The '''case statement''' is preferred when there are many items to select from.
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|The '''case''' statement is preferred when there are many items to select from.
  
 
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|It is usually used to implement '''menus''' in a script.
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|It is usually used to implement '''menu'''s in a script.
  
 
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|'''case''' space '''$(dollar) VARIABLE''' space '''in''' '''match_1''' close round brackets space '''commands''' and semicolon twice
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|'''case space $(dollar) VARIABLE space in match_1 close round-bracket space commands''' and semicolon twice
  
 
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|'''match_n''' close round bracket space '''commands''' and semicolon twice '''asterisk''' close round bracket space '''command_to_execute_by_default''' and semicolon twice '''esac'''.
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|'''match_n close round-bracket space commands''' and semicolon twice asterisk close round=bracket space '''command_to_execute_by_default''' and semicolon twice '''esac'''.
  
 
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|It will check if any one of these '''strings''' matches '''VARIABLE. '''
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|It will check if any one of these '''strings''' matches '''VARIABLE.'''
  
 
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|If yes, then all the '''commands''' until the double''' semicolon (;;) '''are executed.
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|If 'yes' then all the '''commands''' until the double semicolon (;;) are executed.
  
 
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|The location of '''bash '''is different in other '''Linux''' flavors like '''CentOS, RedHat etc.'''
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|The location of '''bash '''is different in other '''Linux''' flavors like '''CentOS, RedHat''' etc.
  
 
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|This '''shebang '''line improves the portability of the script on any '''GNU/Linux''' system.
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|This '''shebang line''' improves the portability of the script on any '''GNU/Linux''' system.
  
 
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| '''df -(hyphen)h displays disk space''' usage in human readable form.
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| '''df -(hyphen)h''' displays '''disk space''' usage in human readable form.
  
 
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|The output is then passed to '''awk 'FNR == 2 {print $5}''''  
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|The output is then passed to '''awk 'FNR == 2 {print $5}' '''  
  
 
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|which extracts the fifth field of the second line.
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|which extracts the fifth '''field''' of the second line.
  
 
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|Eventually, the output is passed to '''cut -(hyphen)d “% -(hyphen)f1” '''to strip out '''% sign.'''
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|Eventually, the output is passed to '''cut -(hyphen)d “% -(hyphen)f1” '''to strip out '''%''' sign.
  
 
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| Next, it compares the '''space''' between 70 and 89 or from 91 to 98;
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| Next, it compares the '''space''' between 70 and 89 or from 91 to 98.
  
 
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| This is the default case condition because the '''asterisk '''will match all strings.
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| This is the default '''case''' condition because the asterisk will match all '''strings'''.
  
 
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| Now go to the''' terminal''' to make the file executable.
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| Now, go to the''' terminal''' to make the file executable.
  
 
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| '''Everything is OK.''' Note that the output will vary depending on your system disk space.
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| ''' "Everything is OK".''' Note that the output will vary depending on your system disk space.
  
 
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| In my machine, as match is found between 0 and 69, it prints '''Everything is OK.'''
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| In my machine, as match is found between 0 and 69, it prints '''"Everything is OK".'''
  
 
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|You will be able to understand which '''case statement''' was executed.
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|You will be able to understand which '''case''' statement was executed.
  
 
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|This brings us to the end of this tutorial. Let us summarize.
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|This brings us to the end of this tutorial. Let us summarize.
  
 
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|05:31
 
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|In this tutorial, we learnt:
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|In this tutorial, we learned:
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* Importance of''' case statement'''  
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* Importance of''' case''' statement
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* Syntax of '''case statement''' with the disc-space example.
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* Syntax of '''case''' statement with the '''disc-space''' example.
  
 
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|Write a menu driven program for mathematical calculation;
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|Write a menu driven program for mathematical calculation-
  
 
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|05:47
 
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| It should take user inputs '''a '''and '''b''';
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|* It should take user inputs 'a' and 'b';
  
 
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| It should ask for mathematical operator (plus +, minus -, division / and multiplication *). Do the calculation,  print the output.
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|* It should ask for mathematical operator (plus +, minus -, division / and multiplication *). * Do the calculation * print the output.
  
 
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|It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this mission is available at: http://spoken-tutorial.org\NMEICT-Intro
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|It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this mission is available at: http://spoken-tutorial.org/NMEICT-Intro
  
 
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Revision as of 18:20, 13 July 2015

Time Narration
00:01 Dear friends, welcome to the spoken tutorial on Case statement in Bash.
00:07 In this tutorial, we will learn:
  • Importance of case statement
  • Syntax of case statement with an example.
00:17 To follow this tutorial, you should have knowledge on basics of Shell scripting.
00:23 If not, for relevant tutorials, please visit our website which is as shown.
00:29 For this tutorial, I am using:
  • Ubuntu Linux 12.04 Operating System and
  • GNU BASH version 4.1.10
00:39 Please note, GNU Bash version 4 or above is recommended to practice this tutorial.
00:47 The Bash shell has two forms of conditional statements- 'if' statement and 'case' statement.
00:56 Case statement can be alternately used in place of if-else statement.
01:03 The case statement is preferred when there are many items to select from.
01:09 It is usually used to implement menus in a script.
01:14 Let us see the syntax.
01:15 case space $(dollar) VARIABLE space in match_1 close round-bracket space commands and semicolon twice
01:27 match_n close round-bracket space commands and semicolon twice asterisk close round=bracket space command_to_execute_by_default and semicolon twice esac.
01:45 The VARIABLE is compared to match_1.
01:48 If it does not match, it moves on to the next case which is match_n.
01:54 It will check if any one of these strings matches VARIABLE.
02:01 If 'yes' then all the commands until the double semicolon (;;) are executed.
02:07 If neither match VARIABLE, the commands associated with the asterisk are executed.
02:14 It is the default case condition because the asterisk will match all strings.
02:21 esac marks the end of case block.
02:26 Let us understand case statement with an example.
02:32 I have already typed the program. So, I will open the file case.sh.
02:38 The program prints a warning message when the disk space reaches a certain limit.
02:45 This is the shebang line.
02:47 The location of bash is different in other Linux flavors like CentOS, RedHat etc.
02:55 Previously used /bin/bash points directly to the binary file.
03:01 env used here, abstracts the true location where bash is located.
03:07 This shebang line improves the portability of the script on any GNU/Linux system.
03:16 df -(hyphen)h displays disk space usage in human readable form.
03:22 The output is piped to sort -rk5 which sorts the fifth column in reverse order.
03:31 The output is then passed to awk 'FNR == 2 {print $5}'
03:38 which extracts the fifth field of the second line.
03:43 Eventually, the output is passed to cut -(hyphen)d “% -(hyphen)f1” to strip out % sign.
03:55 This is the first line of case statement.
03:59 Here, we compare the space between 0 and 69.
04:04 If match is found, it prints "Everything is OK”
04:08 Next, it compares the space between 70 and 89 or from 91 to 98.
04:17 If match is found, it prints “Clean out. There's a partition that is $(dollar)space % full.”
04:27 Here, it compares the space with 99.
04:30 If match is found, it prints “Hurry. There's a partition at $(Dollar) space %!”
04:39 This is the default case condition because the asterisk will match all strings.
04:45 And this is the end of case statement.
04:48 Now, go to the terminal to make the file executable.
04:52 Type: chmod plus x case dot sh
04:57 Type: dot slash case dot sh
05:02 "Everything is OK". Note that the output will vary depending on your system disk space.
05:10 In my machine, as match is found between 0 and 69, it prints "Everything is OK".
05:18 Check the message printed on your machine.
05:20 You will be able to understand which case statement was executed.
05:27 This brings us to the end of this tutorial. Let us summarize.
05:31 In this tutorial, we learned:
  • Importance of case statement
  • Syntax of case statement with the disc-space example.
05:41 As an assignment:
05:42 Write a menu driven program for mathematical calculation-
05:47 * It should take user inputs 'a' and 'b';
05:51 * It should ask for mathematical operator (plus +, minus -, division / and multiplication *). * Do the calculation * print the output.
06:02 Watch the video available at the link shown below.
06:06 It summarizes the Spoken-Tutorial project.
06:08 If you do not have good bandwidth, you can download and watch it.
06:14 The Spoken Tutorial Project team:
06:16 Conducts workshops using spoken tutorials ;

Gives certificates to those who pass an online test.

06:23 For more details, please write to contact@spoken-tutorial.org
06:31 Spoken Tutorial project is a part of the Talk to a Teacher project.
06:35 It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this mission is available at: http://spoken-tutorial.org/NMEICT-Intro
06:48 The script has been contributed by FOSSEE and spoken-tutorial team.
06:53 This is Ashwini from IIT Bombay. Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14

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