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

Welcome to the spoken tutorial on Case statement in Bash.

• Importance of case statement
• Syntax of case statement
• with an Example

Basics of Shell Scripting.

If not, for relevant tutorials please visit our website which is as shown.

System requirements

• Ubuntu Linux 12.04 Operating System and
• GNU BASH version 4.1.10

Please note, GNU Bash version 4 or above is recommended to practice this tutorial.

Case Statement

• These are the if statement and the case statement.
• Case statement can be alternately used in place of if-else statement

Case statement

• The case statement is preferred when there are many items to select from.

• It is usually used to implement menus in a script.

Case Statement

Syntax:

case $VARIABLE inmatch_1) commands

;;match_n) commands

;;*) command_to_execute_by_default

;;esac

Let us see the syntax.

case space dollar VARIABLE space in

match_1 close round brackets space commands

and semicolon twice

match_n close round bracket space commands

and semicolon twice

asterisk close round bracket space command_to_execute_by_default

and semicolon twice

esac

Working Of Case Statement

If it does not match, it moves on to the next case which is match_n.

It will check if any one of these strings matches VARIABLE.

If yes, then all the commands until the double semicolon (;;) are executed.

Working Of Case Statement

It is the default case condition because the asterisk will match all strings.

esac marks the end of case block.

The program prints a warning message when the disk space reaches a certain limit.

#!/usr/bin/env bash

The location of bash is different in other Linux flavours like CentOS, RedHat etc.

Previously used /bin/bash points directly to the binary file.

env used here, abstracts the true location where bash is located.

This shebang line improves the portability of the script on any GNU/Linux system.

The output is piped to sort -rk5, which sorts the fifth column in reverse order.

The output is then passed to awk 'FNR == 2 {print $5}' which extracts the fifth field of the second line.

Eventually, the output is passed to cut -d “% -f1” to strip out % sign.

echo "Everything is OK"

;;

If match is found, it prints

“Everything is OK”

echo "Clean out. There's a partition that is $space % full."

;;

If match is found, it prints

“Clean out. There's a partition that is $space % full.”

echo " Hurry. There's a partition at $space %!"

;;

If match is found, it prints

“Hurry. There's a partition at $space %!”

echo "This is nonexistent amount of disk space..."

;;

Type: chmod space plus x space case dot sh

Now type dot slash case dot sh

Everything is OK.

Note that the output will vary depending on your system diskspace.

Everything is OK

“Everything is OK”.

Check the message printed on your machine.

You will be able to understand which case statement was executed.

Summary

This brings us to the end of this tutorial. Let us summarize.

In this tutorial we learnt,

• Importance of case statement
• Syntax of case statement
• With the disc space example

Assignment

Write a menu driven program for mathematical calculation

• It should take user inputs a and b
• It should ask for mathematical opertator(plus +, minus -, division / and multiplication *)
• Do the calculation
• Print the output

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This is Ashwini from IIT Bombay.

Thank you for joining.