BASH/C2/Case-statement/English-timed
From Script | Spoken-Tutorial
| 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. 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: 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. |
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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. |
