Difference between revisions of "BASH/C3/Basics-of-Redirection-(error-handling)/English-timed"
From Script | Spoken-Tutorial
Sandhya.np14 (Talk | contribs) |
Sandhya.np14 (Talk | contribs) |
||
Line 20: | Line 20: | ||
|- | |- | ||
| 00:10 | | 00:10 | ||
− | |* | + | |* '''input''' and '''output''' in '''Bash''' |
|- | |- | ||
| 00:12 | | 00:12 | ||
− | |* Redirection and file descriptors | + | |* '''Redirection''' and '''file descriptors''' |
|- | |- | ||
| 00:15 | | 00:15 | ||
− | |* | + | |* '''standard input''' |
|- | |- | ||
| 00:16 | | 00:16 | ||
− | |* | + | |* '''standard output''' |
|- | |- | ||
| 00:18 | | 00:18 | ||
− | |* | + | |* '''standard error''' |
|- | |- | ||
Line 48: | Line 48: | ||
|- | |- | ||
| 00:28 | | 00:28 | ||
− | |If not, for relevant tutorials, please visit our website which is as shown. | + | |If not, for relevant tutorials, please visit our website which is as shown. http://www.spoken-tutorial.org |
|- | |- | ||
| 00:34 | | 00:34 | ||
− | | For this tutorial, I am using | + | | For this tutorial, I am using: |
|- | |- | ||
| 00:36 | | 00:36 | ||
− | | '''Ubuntu Linux''' 12.04 '''Operating System''' and | + | |* '''Ubuntu Linux''' 12.04 '''Operating System''' and |
|- | |- | ||
| 00:40 | | 00:40 | ||
− | | '''GNU BASH''' version 4.2 | + | |* '''GNU BASH''' version 4.2 |
|- | |- | ||
Line 84: | Line 84: | ||
|- | |- | ||
| 01:18 | | 01:18 | ||
− | | In GNU/Linux everything is a file, including the hardware. | + | | In '''GNU/Linux''' everything is a file, including the hardware. |
|- | |- | ||
Line 92: | Line 92: | ||
|- | |- | ||
| 01:27 | | 01:27 | ||
− | |* | + | |* '0' for '''input''' i.e. '''keyboard''' |
|- | |- | ||
| 01:31 | | 01:31 | ||
− | |* | + | |* '1' for '''output''' i.e. '''screen ''' |
|- | |- | ||
| 01:34 | | 01:34 | ||
− | |* | + | |* '2' for '''error '''i.e. '''screen. ''' |
|- | |- | ||
|01:38 | |01:38 | ||
− | | | + | |0, 1, 2 are '''POSIX '''numbers and also known as '''file descriptors''' '''(FD'''). |
|- | |- | ||
| 01:46 | | 01:46 | ||
− | | A re-director uses '''POSIX''' numbers to talk with a user or other program. | + | | A '''re-director''' uses '''POSIX''' numbers to talk with a user or other program. |
|- | |- | ||
| 01:54 | | 01:54 | ||
− | | '''Standard input''': | + | | '''Standard input''': standard input is the default input method. |
|- | |- | ||
Line 136: | Line 136: | ||
|- | |- | ||
| 02:22 | | 02:22 | ||
− | | The syntax is- '''command''' space less than symbol space '''filename''' | + | | The syntax is- '''command''' space less than symbol space '''filename'''. |
|- | |- | ||
Line 144: | Line 144: | ||
|- | |- | ||
| 02:34 | | 02:34 | ||
− | | I have typed some | + | | I have typed some code in this file. |
|- | |- | ||
Line 164: | Line 164: | ||
|- | |- | ||
| 02:57 | | 02:57 | ||
− | | '''sort '''command does the | + | | '''sort '''command does the sorting of numbers present in ''' file dot txt'''. |
|- | |- | ||
Line 176: | Line 176: | ||
|- | |- | ||
| 03:10 | | 03:10 | ||
− | | Open the '''terminal''' using '''Ctrl, Alt''' and '''T''' simultaneously on your keyboard. | + | | Open the '''terminal''' using '''Ctrl, Alt''' and '''T''' keys simultaneously on your keyboard. |
|- | |- | ||
|03:18 | |03:18 | ||
− | | Before that, let us see the | + | | Before that, let us see the contents of '''file dot txt'''. |
|- | |- | ||
Line 196: | Line 196: | ||
|- | |- | ||
| 03:35 | | 03:35 | ||
− | | Now type: '''chmod space plus x space redirection dot sh''' | + | | Now type: '''chmod space plus x space redirection dot sh'''. |
|- | |- | ||
Line 224: | Line 224: | ||
|- | |- | ||
| 04:03 | | 04:03 | ||
− | | '''Standard output''': | + | | '''Standard output''': standard output is used by all commands to display output. |
|- | |- | ||
| 04:10 | | 04:10 | ||
− | | The '''default | + | | The '''default''' '''output''' is displayed on the screen. |
|- | |- | ||
Line 248: | Line 248: | ||
|- | |- | ||
| 04:35 | | 04:35 | ||
− | | Let me go back to | + | | Let me go back to our file '''redirection dot sh'''. |
|- | |- | ||
Line 264: | Line 264: | ||
|- | |- | ||
| 04:59 | | 04:59 | ||
− | | The output of | + | | The output of 'ls' will be stored in '''ls_file dot txt '''. |
|- | |- | ||
| 05:06 | | 05:06 | ||
− | | | + | | 'ls' command lists the information about files in that particular directory. |
|- | |- | ||
Line 276: | Line 276: | ||
|- | |- | ||
| 05:19 | | 05:19 | ||
− | | Let me clear the '''prompt'''. First, let us type | + | | Let me clear the '''prompt'''. First, let us type 'ls' and see the output. |
|- | |- | ||
Line 308: | Line 308: | ||
|- | |- | ||
| 06:06 | | 06:06 | ||
− | | '''Standard error '''is the default output error | + | | '''Standard error''': standard error is the default '''output error'''. |
|- | |- | ||
| 06:12 | | 06:12 | ||
− | | It is used to write all system errors | + | | It is used to write all system errors. |
|- | |- | ||
Line 328: | Line 328: | ||
|- | |- | ||
| 06:32 | | 06:32 | ||
− | | '''Two greater than symbol (2>)''' is error redirection symbol | + | | '''Two greater than symbol (2>)''' is '''error redirection''' symbol. |
|- | |- | ||
| 06:36 | | 06:36 | ||
− | | Syntax is '''command space 2 greater than space error dot txt''' | + | | Syntax is '''command space 2 greater than symbol space error dot txt'''. |
|- | |- | ||
| 06:44 | | 06:44 | ||
− | | Let me go back to the file '''redirection dot sh''' | + | | Let me go back to the file '''redirection dot sh'''. |
|- | |- | ||
| 06:49 | | 06:49 | ||
− | | We will comment the previous line. i.e. | + | | We will comment the previous line. i.e.'ls'. |
|- | |- | ||
| 06:54 | | 06:54 | ||
− | | Below it type ''' rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt.''' | + | | Below it, type: ''' rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt.''' |
|- | |- | ||
| 07:11 | | 07:11 | ||
− | | The error output is redirected to '''error dot txt file.''' | + | | The '''error output''' is redirected to '''error dot txt file.''' |
|- | |- | ||
| 07:17 | | 07:17 | ||
− | | Now, | + | | Now, click on '''Save''' and switch to the '''terminal'''. |
|- | |- | ||
Line 420: | Line 420: | ||
|- | |- | ||
| 08:35 | | 08:35 | ||
− | |* Redirection and file descriptors | + | |* '''Redirection''' and '''file descriptors''' |
|- | |- | ||
| 08:38 | | 08:38 | ||
− | |* | + | |* '''standard input''' using '<' (less than) symbol |
|- | |- | ||
| 08:42 | | 08:42 | ||
− | |* | + | |* '''standard output''' using '>' (greater than) symbol |
|- | |- | ||
| 08:47 | | 08:47 | ||
− | |* | + | |* '''standard error''' using '2>' (2 greater than symbol). |
|- | |- | ||
Line 440: | Line 440: | ||
|- | |- | ||
| 08:54 | | 08:54 | ||
− | | | + | | write a program in any language like C, C++, Java |
|- | |- | ||
| 08:59 | | 08:59 | ||
− | | | + | | and '''redirect''' the '''output''' or '''error''' to a new file. |
|- | |- | ||
| 09:04 | | 09:04 | ||
− | | Or, create a '''text file''' with some | + | | Or, create a '''text file''' with some contents like your name, address. |
|- | |- | ||
| 09:11 | | 09:11 | ||
− | | '''Redirect''' the | + | | '''Redirect''' the contents to a new file. |
|- | |- | ||
Line 472: | Line 472: | ||
|- | |- | ||
| 09:30 | | 09:30 | ||
− | | Conducts workshops using spoken tutorials. | + | |* Conducts workshops using spoken tutorials. |
|- | |- | ||
| 09:34 | | 09:34 | ||
− | | Gives certificates to those who pass an online test. | + | |* Gives certificates to those who pass an online test. |
|- | |- | ||
Line 496: | Line 496: | ||
|- | |- | ||
| 10:04 | | 10:04 | ||
− | | The | + | | The script has been contributed by FOSSEE and Spoken-Tutorial teams. |
|- | |- |
Revision as of 15:39, 15 July 2015
Title of script: Basics of redirection
Author: Lavitha Pereira
Keywords: Video tutorial, redirection, file descriptors, standard input, standard output, standard error
Time | Narration |
00:01 | Dear friends, welcome to the spoken tutorial on Basics of redirection. |
00:07 | In this tutorial, we will learn: |
00:10 | * input and output in Bash |
00:12 | * Redirection and file descriptors |
00:15 | * standard input |
00:16 | * standard output |
00:18 | * standard error |
00:19 | with the help of some examples. |
00:22 | To follow this tutorial, you should have knowledge of Shell Scripting in BASH. |
00:28 | If not, for relevant tutorials, please visit our website which is as shown. http://www.spoken-tutorial.org |
00:34 | For this tutorial, I am using: |
00:36 | * Ubuntu Linux 12.04 Operating System and |
00:40 | * GNU BASH version 4.2 |
00:43 | Please note, GNU Bash version 4 or above is recommended for practice. |
00:50 | In GNU/Linux we can send output to a file or read input from a file. |
00:58 | Each Shell command has its own inputs and outputs. |
01:03 | Input and output is redirected using a special notation interpreted by the Shell. |
01:11 | Changing the default path of input or output is called as redirection. |
01:18 | In GNU/Linux everything is a file, including the hardware. |
01:24 | Common return values are: |
01:27 | * '0' for input i.e. keyboard |
01:31 | * '1' for output i.e. screen |
01:34 | * '2' for error i.e. screen. |
01:38 | 0, 1, 2 are POSIX numbers and also known as file descriptors (FD). |
01:46 | A re-director uses POSIX numbers to talk with a user or other program. |
01:54 | Standard input: standard input is the default input method. |
02:00 | It is used by all commands to read input. |
02:04 | It is denoted by zero (0). |
02:07 | Also known as stdin (Standard input). |
02:13 | The default standard input is the keyboard. |
02:17 | Less than symbol is input redirection symbol. |
02:22 | The syntax is- command space less than symbol space filename. |
02:30 | Let me open a file named redirection dot sh. |
02:34 | I have typed some code in this file. |
02:37 | This is the shebang line. |
02:41 | Type: sort' space less than symbol space file dot txt. |
02:48 | This is an example of input redirection. |
02:52 | The input is taken from file file dot txt. |
02:57 | sort command does the sorting of numbers present in file dot txt. |
03:04 | Click on Save. |
03:06 | Let us run the file redirection dot sh. |
03:10 | Open the terminal using Ctrl, Alt and T keys simultaneously on your keyboard. |
03:18 | Before that, let us see the contents of file dot txt. |
03:23 | Type: cat space file dot txt. |
03:27 | Press Enter. |
03:30 | You can see that the file contains series of numbers. |
03:35 | Now type: chmod space plus x space redirection dot sh. |
03:43 | Press Enter. |
03:45 | Type: dot slash redirection dot sh |
03:48 | Press Enter. |
03:51 | We can see the output on the terminal after sorting. |
03:56 | The numbers are sorted in ascending order. |
04:00 | Come back to our slides. |
04:03 | Standard output: standard output is used by all commands to display output. |
04:10 | The default output is displayed on the screen. |
04:14 | It is denoted by number one (1). |
04:17 | Also known as stdout (Standard output). |
04:23 | ( > )Greater than symbol is the output redirection symbol. |
04:28 | Syntax is command space greater than symbol space filename. |
04:35 | Let me go back to our file redirection dot sh. |
04:41 | Comment the previous line i.e. sort. |
04:45 | Below it, type: ls space greater than symbol space ls underscore file.txt |
04:55 | This is an example of output redirection. |
04:59 | The output of 'ls' will be stored in ls_file dot txt . |
05:06 | 'ls' command lists the information about files in that particular directory. |
05:14 | Now, save the file and switch to the terminal. |
05:19 | Let me clear the prompt. First, let us type 'ls' and see the output. |
05:28 | Now press the up-arrow key thrice. |
05:33 | Recall the previous command dot slash redirection dot sh. |
05:38 | And Press Enter. |
05:41 | Now let us check whether the output is redirected correctly. |
05:46 | Type: gedit space ls underscore file dot txt and press Enter. |
05:56 | We can now see the output in this file. So our redirect was successful. |
06:03 | Come back to our slides. |
06:06 | Standard error: standard error is the default output error. |
06:12 | It is used to write all system errors. |
06:16 | It is denoted by number two (2). |
06:20 | Also known as stderr (Standard error). |
06:25 | The default standard error output is visible on the screen or monitor. |
06:32 | Two greater than symbol (2>) is error redirection symbol. |
06:36 | Syntax is command space 2 greater than symbol space error dot txt. |
06:44 | Let me go back to the file redirection dot sh. |
06:49 | We will comment the previous line. i.e.'ls'. |
06:54 | Below it, type: rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt. |
07:11 | The error output is redirected to error dot txt file. |
07:17 | Now, click on Save and switch to the terminal. |
07:22 | We will type a command to see the error first. |
07:26 | Type: rm space slash tmp slash 4815 dot txt |
07:36 | Press Enter. |
07:38 | The error displayed is- |
07:40 | rm: cannot remove slash tmp slash 4815 dot txt: No such file or directory. |
07:49 | Now we will execute our file. |
07:53 | Press the up-arrow key |
07:55 | and recall the previous command dot slash redirection dot sh. |
08:01 | Press Enter. |
08:03 | Now let us check whether the error is redirected. |
08:07 | Type: gedit space error dot txt and press Enter. |
08:15 | We can now see the error redirected to file error dot txt. |
08:22 | This brings us to the end of this tutorial. |
08:26 | Let us summarize. |
08:28 | In this tutorial, we learned: |
08:31 | * Input and output in Bash |
08:35 | * Redirection and file descriptors |
08:38 | * standard input using '<' (less than) symbol |
08:42 | * standard output using '>' (greater than) symbol |
08:47 | * standard error using '2>' (2 greater than symbol). |
08:52 | As an assignment- |
08:54 | write a program in any language like C, C++, Java |
08:59 | and redirect the output or error to a new file. |
09:04 | Or, create a text file with some contents like your name, address. |
09:11 | Redirect the contents to a new file. |
09:15 | Watch the video available at the link shown below. |
09:19 | It summarizes the Spoken-Tutorial project. |
09:23 | If you do not have good bandwidth, you can download and watch it. |
09:28 | The Spoken Tutorial project team: |
09:30 | * Conducts workshops using spoken tutorials. |
09:34 | * Gives certificates to those who pass an online test. |
09:38 | For more details, please write to contact@spoken-tutorial.org |
09:46 | Spoken Tutorial project is a part of the Talk to a Teacher project. |
09:50 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
09:58 | More information on this mission is available at the link shown below. |
10:04 | The script has been contributed by FOSSEE and Spoken-Tutorial teams. |
10:10 | This is Ashwini from IIT Bombay, signing off. Thank you for joining. |