Difference between revisions of "BASH/C2/Command-Line-arguments-and-Quoting/English-timed"

| Welcome to the spoken tutorial on''' Command line arguments and Quoting in BASH'''

| In this tutorial, we will learn about

|* '''Command line Arguments '''and

|* '''Quoting'''

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

| For this tutorial I am using  

|* '''Ubuntu Linux 12.04''' OS  

|* '''GNU Bash''' version '''4.1.10'''

|'''GNU Bash '''version '''4''' or above is recommended for practice.

|* '''Shell script''' can accept '''arguments''' from the '''command line'''.

|* An '''argument''' is passed to a '''program''' being called.

|* Any number of '''arguments''' can be passed to a '''program'''.

| Let us open the '''terminal''' by pressing '''Ctrl Alt andT''' keys simultaneously on your keyboard.

| I have already written the code in the file named '''arg.sh'''

|On the '''terminal,''' let me open this file by typing,

|'''gedit''' '''space arg.sh space ampersand sign'''

|We use the '''ampersand to''' free up the '''prompt'''.

|Now, Press''' Enter.'''

| The text editor is opened.

|Let me explain the code now.

| This is the '''shenbang '''line.

| This line will print the '''Zeroth''' '''argument'''.

|Here, '''$0 (Dollar zero) '''will print the name of the shell script.

|This in turn means that, the '''zeroth  argument''' is the name of the '''program''' itself.

| Let us execute the program and see.

|Switch to the terminal.

| First make the file executable by typing,

|Press '''Enter'''

| Now type '''dot slash arg.sh'''

|Press Enter

 

| The output is displayed as: '''Zeroth argument is arg.sh'''

| Now come back to our editor and type the three lines as shown here.

| '''$1 (Dollar one) '''represents the first '''argument''' passed to the '''program''' from the''' command line'''.

|'''$2''' '''(Dollar two) '''represents the second '''argument''' passed to the '''program'''.

|  And '''$3 (Dollar three) '''represents the '''third argument'''

| Now click on '''Save'''

 

| Let us execute the program and see.

|Press the uparrow key  press '''Enter'''

| We see that the zeroeth '''argument''' is printed.

|But the first, second and third '''arguments''' are blank.

| Hence press the uparrow key and type: '''sunday monday and tuesday.'''

|Press '''Enter'''

| You can see that the first second and third '''arguments''' are '''Sunday Monday and Tuesday'''

| Now switch back to our editor. Press '''Enter'''

|Now type the line as shown here.

| '''$12 (Dollar twelve) '''represents the''' twelveth '''argument.

| To write an '''argument''' greater than 9, we need to use '''curly brackets'''.

|Else '''bash''' will only take the '''argument''' of the integer in the '''ten's place'''.

|And you will not get expected output.

|Let us execute the program.

| Hence Type '''dot slash arg.sh space 1 to 13''' Now press enter

| Come back to our editor.

|And type the line as shown here.

| '''$# (Dollar hash)''' gives the total number of '''arguments''' that have been passed to a program.

|Let us execute.

 

| Switch to the terminal.

| Let us execute. Press the uparrow key and press '''Enter.'''

|Now switch to the editor.

|Press '''Enter''' and '''type''' the lines as shown here.

| '''$* (Dollar asterix)''' will print all the '''arguments''' on a '''''single line'''. ''

| We will test this with the help of a simple''' for '''loop.

| We will analyse this '''for '''loop at the time of execution.

| Now click on '''Save.'''Switch to the terminal.

| Let me clear the prompt.

| Now let us type, '''dot slash arg.sh space sunday monday and tuesday'''

| Press''' Enter'''

|As already said '''$*''' will print all the '''arguments''' on a single line.

| We see that''' '''all the '''arguments''' are printed on the '''''single line'''.''

| Now move back to our program and '''type''' the lines as shown here.

| '''$@ (Dollar at)''' will also print all the '''arguments'''.  

| However, this time each '''argument''' will be printed on '''separate line'''.

| This is another '''for''' loop, which will print each '''argument''' in a separate line.

| Let us see how. Click on '''Save'''

| Switch to the terminal.

|Press the''' uparrow key.'''

| Press''' Enter''' You can see the difference now.

|This is the output for the 2nd '''for loop.'''

| Now lets move on to '''quoting''' in '''BASH'''

|Switch to the slides.

| There are three types of quotes  

|'''Double quote'''

 

| '''Single quote'''

| '''Backslash'''

 

|* '''Double quote '''substitutes the value of '''variables''' and '''commands'''

|* Example '''echo “Username is $USER”'''

|* It displays your '''username ''' of the system.

| Let me clear the prompt.

|Now type  '''echo''' space within double quotes '''Username''' space ''' is dollar USER ''' in capitals.

| Press '''Enter'''

 

| The '''username '''of the system is printed.

| The output will vary according to your system.

| Now move back to slides.

| * '''Single quotes''' preserves the literal meaning of each character of the given string.

| * It is used to turn off special meaning of all characters.

| Type '''echo''' space within single quote '''Username  is dollar USER''' in capital

| Press '''Enter'''

| The output is '''Username is $USER'''

| It does not substitute the value of''' variable $USER'''

| Switch back to our slides.

| * '''Backslash''' removes the special meaning from a single character

|* It is used as an escape character in '''BASH'''

|Now Type '''echo''' space within double quote '''Username is backslash dollar USER ''' (in capital)

|Let's try this command so press '''Enter.'''

| The output is '''Username is $USER'''

|In this example the''' backslash '''removes the special meaning of ('''Dollar''') '''$ '''symbol.  

|'''$USER '''is just treated as a string without any special functionality.

|Switch back to our slides.

|Let us summarize.

 

| In this tutorial we learnt,

|* '''Command line arguments'''

|* Functionality of  Double quote, Single quote and Backslash

| Watch the video available at the link shown below

|It summarises the Spoken Tutorial project  

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| The script has been contributed by FOSSEE and spoken-tutorial Team.

|And this is Ashwini Patil from IIT Bombay signing off. Thank you for joining.