Difference between revisions of "BASH/C2/Command-Line-arguments-and-Quoting/English-timed"
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| − | | Now let's move on to '''quoting''' in '''BASH''' | + | | Now let's move on to '''quoting''' in '''BASH'''. |
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| − | | The output is '''Username is $USER''' | + | | The output is '''Username is $USER'''. |
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Revision as of 10:09, 2 July 2015
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on Command line arguments and Quoting in BASH. |
| 00:08 | In this tutorial, we will learn about: |
| 00:11 | * Command line Arguments and |
| 00:13 | * Quoting. |
| 00:15 | To follow this tutorial, you should be familiar with the Linux Operating System. |
| 00:20 | If not, for relevant tutorials please visit our website which is as shown. |
| 00:26 | For this tutorial, I am using: |
| 00:29 | * Ubuntu Linux 12.04 OS |
| 00:33 | * GNU Bash version 4.1.10 |
| 00:37 | GNU Bash version 4 or above is recommended for practice. |
| 00:43 | Shell script can accept arguments from the command line. |
| 00:46 | An argument is passed to a program being called. |
| 00:52 | Any number of arguments can be passed to a program. |
| 00:57 | Let us open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard. |
| 01:06 | I have already written the code in the file named arg.sh. |
| 01:12 | On the terminal, let me open this file by typing: |
| 01:16 | gedit space arg.sh space ampersand sign(&). |
| 01:23 | We use the ampersand to free up the prompt. |
| 01:27 | Now, press Enter. |
| 01:30 | The text-editor is opened. |
| 01:33 | Let me explain the code now. |
| 01:36 | This is the shebang line. |
| 01:39 | This line will print the zeroth argument. |
| 01:43 | Here, $0 (Dollar zero) will print the name of the shell script. |
| 01:48 | This, in turn, means that the zeroth argument is the name of the program itself. |
| 01:55 | Let us execute the program and see. |
| 01:59 | Switch to the terminal. |
| 02:01 | First, make the file executable by typing: |
| 02:05 | chmod space plus x space arg.sh |
| 02:12 | Press Enter. |
| 02:14 | Now, type: dot slash arg.sh |
| 02:18 | Press Enter. |
| 02:19 | The output is displayed as: Zeroth argument is arg.sh. |
| 02:26 | Now, come back to our editor and type the three lines as shown here. |
| 02:33 | $1 (Dollar one) represents the first argument passed to the program from the command line. |
| 02:40 | $2 (Dollar two) represents the second argument passed to the program. |
| 02:44 | And $3 (Dollar three) represents the third argument. |
| 02:48 | Now, click on Save. |
| 02:49 | Let us execute the program and see. |
| 02:52 | Press the up-arrow key, press Enter. |
| 02:57 | We see that the zeroth argument is printed. |
| 03:00 | But the first, second and third arguments are blank. |
| 03:05 | This is because the command line arguments are given during execution. |
| 03:11 | Hence, press the up-arrow key and type: sunday monday and tuesday |
| 03:18 | Press Enter. |
| 03:21 | You can see that the first, second and third arguments are sunday monday and tuesday. |
| 03:28 | Now switch back to our editor. Press Enter. |
| 03:33 | Now type the line as shown here. |
| 03:37 | $12 (Dollar twelve) represents the twelveth argument. |
| 03:41 | To write an argument greater than 9, we need to use curly brackets |
| 03:46 | else bash will only take the argument of the integer in the ten's place |
| 03:53 | and you will not get expected output. |
| 03:57 | Now click on Save. |
| 03:59 | Let us execute the program. |
| 04:01 | Switch to the terminal. |
| 04:04 | Let me clear the prompt. |
| 04:07 | Now we need to give 12 or 13 arguments to the program. |
| 04:12 | Hence, type: dot slash arg.sh space 1 to 13. Now press Enter. |
| 04:23 | You can see that the 12th argument is 12. |
| 04:27 | Come back to our editor |
| 04:30 | and type the line as shown here. |
| 04:34 | $# (Dollar hash) gives the total number of arguments that have been passed to a program. |
| 04:40 | Now click on Save. |
| 04:43 | Let us execute. |
| 04:44 | Switch to the terminal. |
| 04:46 | Let us execute. Press the up-arrow key and press Enter. |
| 04:52 | We can see that the total arguments are 13. |
| 04:57 | Now switch to the editor. |
| 05:00 | Press Enter and type the lines as shown here. |
| 05:04 | $* (Dollar asterisk) will print all the arguments on a single line. |
| 05:10 | We will test this with the help of a simple for loop. |
| 05:14 | We will analyze this for loop at the time of execution. |
| 05:18 | Now click on Save. Switch to the terminal. |
| 05:22 | Let me clear the prompt. |
| 05:26 | Now, let us type: dot slash arg.sh space sunday monday and tuesday |
| 05:35 | Press Enter. |
| 05:38 | You can see that the total number of arguments are 3 as we have passed 3 arguments to our program. |
| 05:46 | As already said, $* will print all the arguments on a single line. |
| 05:54 | And this is the output for the for loop. |
| 05:57 | We see that all the arguments are printed on the single line. |
| 06:02 | Now, move back to our program and type the lines as shown here. |
| 06:09 | $@ (Dollar at) will also print all the arguments. |
| 06:13 | However, this time each argument will be printed on separate line. |
| 06:20 | This is another for loop which will print each argument in a separate line. |
| 06:26 | Let us see how. Click on Save. |
| 06:29 | Switch to the terminal. |
| 06:32 | Press the up-arrow key. |
| 06:34 | Press Enter. You can see the difference now. |
| 06:39 | These are the arguments printed by $@. |
| 06:43 | $@ prints each argument on separate line. |
| 06:47 | This is the output for the 2nd for loop. |
| 06:52 | Now let's move on to quoting in BASH. |
| 06:55 | Switch to the slides. |
| 06:57 | There are three types of quotes: |
| 06:59 | * Double quote |
| 07:00 | * Single quote |
| 07:02 | * Backslash. |
| 07:03 | Double quote substitutes the value of variables and commands. |
| 07:09 | Example echo “Username is $USER”. |
| 07:13 | It displays your username of the system. |
| 07:17 | Switch to the Terminal. |
| 07:20 | Let me clear the prompt. |
| 07:23 | Now, type: echo space within double quotes Username space is dollar USER in capitals. |
| 07:34 | Press Enter. |
| 07:35 | The username of the system is printed. |
| 07:39 | The output will vary according to your system. |
| 07:42 | Now move back to slides. |
| 07:46 | Single quotes preserves the literal meaning of each character of the given string. |
| 07:53 | It is used to turn off special meaning of all characters. |
| 07:58 | Switch to the Terminal. |
| 08:01 | Type: echo space within single quote Username is dollar USER in capital. |
| 08:10 | Press Enter. |
| 08:12 | The output is Username is $USER. |
| 08:16 | In this example, it prints all the characters which appear within the single quotes. |
| 08:23 | It does not substitute the value of variable $USER. |
| 08:28 | Switch back to our slides. |
| 08:31 | Backslash removes the special meaning from a single character. |
| 08:37 | It is used as an escape character in BASH. |
| 08:42 | Switch to the Terminal. |
| 08:44 | Now, type: echo space within double quote Username is backslash dollar USER (in capital). |
| 08:55 | Since we have given double quotes, we expect the echo command to display the username. |
| 09:02 | Let's try this command, so press Enter. |
| 09:06 | The output is Username is $USER. |
| 09:10 | In this example the backslash removes the special meaning of (Dollar) $ symbol. |
| 09:16 | $USER is just treated as a string without any special functionality. |
| 09:22 | This brings us to the end of this tutorial. |
| 09:25 | Switch back to our slides. |
| 09:27 | Let us summarize. |
| 09:28 | In this tutorial, we learnt: |
| 09:31 | * Command line arguments |
| 09:33 | * Functionality of Double quote, Single quote and Backslash. |
| 09:39 | Watch the video available at the link shown below. |
| 09:42 | It summarizes the Spoken Tutorial project. |
| 09:45 | If you do not have good bandwidth, you can download and watch it. |
| 09:51 | The Spoken Tutorial Project team: Conducts workshops using spoken tutorials. |
| 09:56 | Gives certificates to those who pass an online test. |
| 10:00 | For more details, please write to contact@spoken-tutorial.org |
| 10:07 | Spoken Tutorial Project is a part of the "Talk to a Teacher" project. |
| 10:10 | It is supported by the National Mission on Education through ICT, MHRD, Government of India.
More information on this mission is available at: http://spoken-tutorial.org\NMEICT-Intro |
| 10:24 | The script has been contributed by FOSSEE and spoken-tutorial team. |
| 10:30 | And this is Ashwini Patil from IIT Bombay, signing off. Thank you for joining. |
