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) |
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| 00:34 | | 00:34 | ||
− | | For this tutorial, I am using | + | | For this tutorial, I am using |
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| 02:07 | | 02:07 | ||
− | | Also known as ''' | + | | Also known as '''stdin (Standard input).''' |
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| 04:10 | | 04:10 | ||
− | | The default output is displayed on the screen. | + | | The '''default output''' is displayed on the '''screen'''. |
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| 04:23 | | 04:23 | ||
− | | ( > )'''Greater than''' symbol is the output redirection symbol | + | | ( > )'''Greater than''' symbol is the '''output redirection''' symbol. |
|- | |- | ||
| 04:28 | | 04:28 | ||
− | | Syntax is ''' | + | | Syntax is '''command''' space greater than symbol space '''filename'''. |
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| 04:35 | | 04:35 | ||
− | | Let me go back to a file '''redirection dot sh''' | + | | Let me go back to a file '''redirection dot sh'''. |
|- | |- | ||
| 04:41 | | 04:41 | ||
− | | Comment the previous line | + | | '''Comment''' the previous line i.e. '''sort'''. |
|- | |- | ||
| 04:45 | | 04:45 | ||
− | | Below it, type ''' ls space greater than space ls underscore file.txt''' | + | | Below it, type: '''ls''' space greater than symbol space '''ls underscore file.txt''' |
|- | |- | ||
| 04:55 | | 04:55 | ||
− | | This is an example of output redirection. | + | | This is an example of '''output redirection'''. |
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| 05:14 | | 05:14 | ||
− | |Now, save the file and switch to the '''terminal''' | + | |Now, '''save''' the file and switch to the '''terminal'''. |
|- | |- | ||
| 05:19 | | 05:19 | ||
− | | Let me clear the prompt. First let us type ''''ls'''' and see the output. | + | | Let me clear the '''prompt'''. First, let us type ''''ls'''' and see the output. |
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| 05:28 | | 05:28 | ||
− | | Now press the ''' | + | | Now press the '''up-arrow''' key thrice. |
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| 05:41 | | 05:41 | ||
− | | Now let us check whether the output is redirected correctly. | + | | Now let us check whether the '''output''' is redirected correctly. |
|- | |- | ||
| 05:46 | | 05:46 | ||
− | | Type '''gedit space ls underscore file dot txt '''and press '''Enter.''' | + | | Type: '''gedit space ls underscore file dot txt '''and press '''Enter.''' |
|- | |- | ||
| 05:56 | | 05:56 | ||
− | | We can now see the output in this file. So our redirect was successful. | + | | We can now see the '''output''' in this file. So our '''redirect''' was successful. |
|- | |- | ||
| 06:03 | | 06:03 | ||
− | | Come back to our slides. | + | | Come back to our '''slides'''. |
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| 07:26 | | 07:26 | ||
− | | Type '''rm space | + | | Type: '''rm space slash tmp slash 4815 dot txt''' |
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| 07:38 | | 07:38 | ||
− | | The error displayed is | + | | The '''error''' displayed is- |
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| 07:40 | | 07:40 | ||
− | | '''rm: cannot remove slash tmp slash 4815 dot txt: No such file or directory''' | + | | '''rm: cannot remove slash tmp slash 4815 dot txt: No such file or directory'''. |
|- | |- | ||
| 07:49 | | 07:49 | ||
− | | Now we will execute our file. | + | | Now we will '''execute''' our file. |
|- | |- | ||
| 07:53 | | 07:53 | ||
− | | Press the ''' | + | | Press the '''up-arrow''' key |
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| 07:55 | | 07:55 | ||
− | | | + | | and recall the previous '''command''' '''dot slash redirection dot sh'''. |
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| 08:03 | | 08:03 | ||
− | | Now let us check whether the error is redirected. | + | | Now let us check whether the '''error''' is redirected. |
|- | |- | ||
| 08:07 | | 08:07 | ||
− | | Type '''gedit space error dot txt''' and press '''Enter.''' | + | | Type: '''gedit space error dot txt''' and press '''Enter.''' |
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| 08:15 | | 08:15 | ||
− | | We can now see the error redirected to file '''error dot txt'''. | + | | We can now see the '''error''' redirected to file '''error dot txt'''. |
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| 08:26 | | 08:26 | ||
− | | Let us | + | | Let us summarize. |
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| 08:28 | | 08:28 | ||
− | | In this tutorial we | + | | In this tutorial, we learned: |
|- | |- | ||
| 08:31 | | 08:31 | ||
− | | | + | |* Input and output in Bash |
|- | |- | ||
| 08:35 | | 08:35 | ||
− | | | + | |* Redirection and file descriptors |
|- | |- | ||
| 08:38 | | 08:38 | ||
− | | Standard input using <(less than) symbol | + | |* 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) | + | |* Standard error using 2> (2 greater than symbol). |
|- | |- | ||
| 08:52 | | 08:52 | ||
− | | As an assignment | + | | As an assignment- |
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| 08:59 | | 08:59 | ||
− | | And redirect the output or error to a new file. | + | | And '''redirect''' the '''output''' or '''error''' to a new file. |
|- | |- | ||
| 09:04 | | 09:04 | ||
− | | Or, create a text file with some content like your name, address. | + | | Or, create a '''text file''' with some content like your name, address. |
|- | |- | ||
| 09:11 | | 09:11 | ||
− | | Redirect the content to a new file. | + | | '''Redirect''' the content to a new file. |
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| 09:19 | | 09:19 | ||
− | | It | + | | It summarizes the Spoken-Tutorial project. |
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| 09:28 | | 09:28 | ||
− | | The Spoken Tutorial | + | | The Spoken Tutorial project team: |
|- | |- | ||
| 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. |
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| 09:46 | | 09:46 | ||
− | | Spoken Tutorial | + | | '''Spoken Tutorial''' project is a part of the '''Talk to a Teacher''' project. |
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| 09:58 | | 09:58 | ||
− | | More information on this | + | | More information on this mission is available at the link shown below. |
|- | |- | ||
| 10:04 | | 10:04 | ||
− | | The script has been contributed by FOSSEE and Spoken-Tutorial teams. | + | | The '''script''' has been contributed by FOSSEE and Spoken-Tutorial teams. |
|- | |- | ||
| 10:10 | | 10:10 | ||
− | | This is Ashwini from IIT Bombay | + | | This is Ashwini from IIT Bombay, signing off. Thank you for joining. |
|} | |} |
Revision as of 10:11, 7 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 simultaneously on your keyboard. |
03:18 | Before that, let us see the content 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 a 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 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 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 content like your name, address. |
09:11 | Redirect the content 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. |