Difference between revisions of "BASH/C3/Basics-of-Redirection-(error-handling)/English-timed"
From Script | Spoken-Tutorial
PoojaMoolya (Talk | contribs) (Created page with "'''Title of script: Basics of redirection''' '''Author:''' Lavitha Pereira '''Keywords: Video tutorial, redirection, file descriptors, standard input, standard output, sta...") |
PoojaMoolya (Talk | contribs) |
||
| Line 6: | Line 6: | ||
| − | {| border=1 | + | {|border=1 |
| − | |''' | + | |''' Time''' |
|'''Narration''' | |'''Narration''' | ||
| Line 89: | Line 89: | ||
| 01:24 | | 01:24 | ||
| Common return values are: | | Common return values are: | ||
| + | |||
|- | |- | ||
| 01:27 | | 01:27 | ||
| '''0''' for '''Input''' i.e. '''Keyboard''' | | '''0''' for '''Input''' i.e. '''Keyboard''' | ||
| + | |||
|- | |- | ||
| 01:31 | | 01:31 | ||
| '''1''' for '''Output''' i.e. '''Screen ''' | | '''1''' for '''Output''' i.e. '''Screen ''' | ||
| + | |||
|- | |- | ||
| 01:34 | | 01:34 | ||
| '''2 '''for '''Error '''i.e. '''Screen ''' | | '''2 '''for '''Error '''i.e. '''Screen ''' | ||
| − | |||
| − | |||
| − | |||
|- | |- | ||
| Line 117: | Line 117: | ||
| 02:00 | | 02:00 | ||
| It is used by all commands to read input. | | It is used by all commands to read input. | ||
| + | |||
|- | |- | ||
| 02:04 | | 02:04 | ||
| It is denoted by zero (0). | | It is denoted by zero (0). | ||
| + | |||
|- | |- | ||
| 02:07 | | 02:07 | ||
| Line 135: | Line 137: | ||
| 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 148: | Line 149: | ||
| 02:37 | | 02:37 | ||
| This is the''' shebang line.''' | | This is the''' shebang line.''' | ||
| − | |||
|- | |- | ||
| 02:41 | | 02:41 | ||
| Type''' sort space less than symbol space file dot txt'' | | Type''' sort space less than symbol space file dot txt'' | ||
| + | |||
|- | |- | ||
| 02:48 | | 02:48 | ||
| This is an example of input redirection. | | This is an example of input redirection. | ||
| − | + | |- | |
| 02:52 | | 02:52 | ||
| The input is taken from file '''file dot txt''' | | The input is taken from file '''file dot txt''' | ||
| + | |||
|- | |- | ||
| 02:57 | | 02:57 | ||
| Line 203: | Line 205: | ||
| 03:45 | | 03:45 | ||
| Type '''dot slash redirection dot sh''' | | Type '''dot slash redirection dot sh''' | ||
| − | |||
|- | |- | ||
| Line 224: | Line 225: | ||
| 04:03 | | 04:03 | ||
| Standard output: Standard output is used by all commands to display output. | | Standard output: Standard output is used by all commands to display output. | ||
| + | |||
|- | |- | ||
| 04:10 | | 04:10 | ||
| The default output is displayed on the screen. | | The default output is displayed on the screen. | ||
| + | |||
|- | |- | ||
| 04:14 | | 04:14 | ||
| Line 342: | Line 345: | ||
| 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.''' | ||
| − | |||
|- | |- | ||
| Line 371: | Line 373: | ||
| 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''' | ||
| − | |||
|- | |- | ||
| Line 396: | Line 397: | ||
| 08:07 | | 08:07 | ||
| Type '''gedit space error dot txt''' and press '''Enter.''' | | Type '''gedit space error dot txt''' and press '''Enter.''' | ||
| − | |||
|- | |- | ||
| Line 429: | Line 429: | ||
| 08:42 | | 08:42 | ||
| Standard output using >(greater than) symbol | | Standard output using >(greater than) symbol | ||
| + | |||
|- | |- | ||
| 08:47 | | 08:47 | ||
| Line 484: | Line 485: | ||
| 09:46 | | 09:46 | ||
| Spoken Tutorial Project is a part of the Talk to a Teacher project. | | Spoken Tutorial Project is a part of the Talk to a Teacher project. | ||
| − | |||
|- | |- | ||
| Line 497: | Line 497: | ||
| 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. | ||
| − | |||
|- | |- | ||
Revision as of 12:35, 21 November 2014
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 redirector 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 stdinb(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 symbol space filename |
| 04:35 | Let me go back to a file redirection dot sh |
| 04:41 | Comment the previous line ie. sort |
| 04:45 | Below it, type ls space greater than 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 uparrow 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 backslash tmp backslash 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 uparrow 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 summarise. |
| 08:28 | In this tutorial we learnt |
| 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 summarises 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 |
