BASH/C2/Case-statement/English-timed
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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 brackets 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 flavours 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 space plus x space 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 diskspace. |
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 learnt, 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 opertator (plus +, minus -, division / and multiplication *). Do the calculation, Print the output |
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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. |