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

| In this tutorial, we will learn:  

* Importance of '''case statement'''

* Syntax of '''case statement''' with an example.  

| To follow this tutorial, you should have knowledge on basics of '''Shell Scripting'''.

| For this tutorial, I am using:

* ''' Ubuntu Linux''' 12.04''' Operating System''' and  

* '''GNU BASH''' version 4.1.10

|  The '''Bash''' '''shell''' has two forms of '''conditional statements'''. '''if statement''' and '''case statement.'''

|'''Case statement '''can be alternately used in place of '''if-else statement'''.

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

|It is usually used to implement '''menus''' in a script.

|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'''.

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

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

|The location of '''bash '''is different in other '''Linux''' flavors like '''CentOS, RedHat etc.'''

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

| '''df -(hyphen)h displays disk space''' usage in human readable form.

|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 -(hyphen)d “% -(hyphen)f1” '''to strip out '''% sign.'''

| Next, it compares the '''space''' between 70 and 89 or from 91 to 98;

| This is the default case condition because the '''asterisk '''will match all strings.

| Now go to the''' terminal''' to make the file executable.

| '''Everything is OK.''' Note that the output will vary depending on your system disk space.

| In my machine, as match is found between 0 and 69, it prints '''Everything is OK.'''

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

|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.

| As an assignment:

 

|Write a menu driven program for mathematical calculation;

| It should take user inputs '''a '''and '''b''';

| It should ask for mathematical operator (plus +, minus -, division / and multiplication *). Do the calculation,  print the output.

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