Difference between revisions of "BASH/C3/Basics-of-Redirection-(error-handling)/English-timed"

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|* Input and output in '''Bash'''
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|* '''input''' and '''output''' in '''Bash'''
  
 
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| 00:12
 
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|* Redirection and file descriptors  
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|* '''Redirection''' and '''file descriptors'''
  
 
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|* Standard input
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|* '''standard input'''
  
 
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|* Standard output
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|* '''standard output'''
  
 
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|* Standard error
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|* '''standard error'''
  
 
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|If not, for relevant tutorials, please visit our website which is as shown. '''(http://www.spoken-tutorial.org)'''
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|If not, for relevant tutorials, please visit our website which is as shown. http://www.spoken-tutorial.org
  
 
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| 00:34
 
| 00:34
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| For this tutorial, I am using  
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| For this tutorial, I am using:
  
 
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| 00:36
 
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| '''Ubuntu Linux''' 12.04 '''Operating System''' and
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|* '''Ubuntu Linux''' 12.04 '''Operating System''' and
  
 
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| 00:40
 
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| '''GNU BASH''' version 4.2
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|* '''GNU BASH''' version 4.2
  
 
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| In GNU/Linux everything is a file, including the hardware.
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| In '''GNU/Linux''' everything is a file, including the hardware.
  
 
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|* '''0''' for '''Input''' i.e. '''Keyboard'''  
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|* '0' for '''input''' i.e. '''keyboard'''  
  
 
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| 01:31
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|* '''1''' for '''Output''' i.e. '''Screen '''
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|* '1' for '''output''' i.e. '''screen '''
  
 
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| 01:34
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|* '''2 '''for '''Error '''i.e. '''Screen. '''
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|* '2' for '''error '''i.e. '''screen. '''
  
 
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|01:38
 
|01:38
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|''0, 1, 2 '''are '''POSIX '''numbers and also known as '''file descriptors''' '''(FD''').  
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|0, 1, 2 are '''POSIX '''numbers and also known as '''file descriptors''' '''(FD''').  
  
 
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| 01:46
 
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| A re-director uses '''POSIX''' numbers to talk with a user or other program.  
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| A '''re-director''' uses '''POSIX''' numbers to talk with a user or other program.  
  
 
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| 01:54
 
| 01:54
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|  '''Standard input''': Standard input is the default input method.
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|  '''Standard input''': standard input is the default input method.
  
 
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| 02:22
 
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|  The syntax is- '''command''' space less than symbol space '''filename'''
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|  The syntax is- '''command''' space less than symbol space '''filename'''.
  
 
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| I have typed some '''code''' in this file.
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| I have typed some code in this file.
  
 
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|  '''sort '''command does the '''sorting '''of numbers present in ''' file dot txt'''.
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|  '''sort '''command does the sorting of numbers present in ''' file dot txt'''.
  
 
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| Open the '''terminal''' using '''Ctrl, Alt''' and '''T''' simultaneously on your keyboard.
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| Open the '''terminal''' using '''Ctrl, Alt''' and '''T''' keys simultaneously on your keyboard.
  
 
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|03:18
 
|03:18
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| Before that, let us see the content of '''file dot txt'''.
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| Before that, let us see the contents of '''file dot txt'''.
  
 
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| Now type: '''chmod space plus x space redirection dot sh'''
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| Now type: '''chmod space plus x space redirection dot sh'''.
  
 
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| '''Standard output''': Standard output is used by all commands to display output.  
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| '''Standard output''': standard output is used by all commands to display output.  
  
 
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|  The '''default output''' is displayed on the '''screen'''.  
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|  The '''default''' '''output''' is displayed on the screen.  
  
 
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| Let me go back to a file '''redirection dot sh'''.
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| Let me go back to our file '''redirection dot sh'''.
  
 
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| The output of ''''ls'''' will be stored in '''ls_file dot txt '''.
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| The output of 'ls' will be stored in '''ls_file dot txt '''.
  
 
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| '''ls '''command lists the information about files in that particular directory.
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| 'ls' command lists the information about files in that particular directory.
  
 
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| Let me clear the '''prompt'''.  First, let us type ''''ls'''' and see the output.
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| Let me clear the '''prompt'''.  First, let us type 'ls' and see the output.
  
 
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|  '''Standard error '''is the default output error  
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|  '''Standard error''': standard error is the default '''output error'''.
  
 
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|  It is used to write all system errors  
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|  It is used to write all system errors.
  
 
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|  '''Two greater than symbol (2>)''' is error redirection symbol  
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|  '''Two greater than symbol (2>)''' is '''error redirection''' symbol.
  
 
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| Syntax is '''command space 2 greater than space error dot txt'''
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| Syntax is '''command space 2 greater than symbol space error dot txt'''.
  
 
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| Let me go back to the file '''redirection dot sh'''
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| Let me go back to the file '''redirection dot sh'''.
  
 
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| We will comment the previous line. i.e.'''ls'''
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| We will comment the previous line. i.e.'ls'.
  
 
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| Below it type ''' rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt.'''
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| Below it, type: ''' rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt.'''
  
 
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| The error output is redirected to '''error dot txt file.'''
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| The '''error output''' is redirected to '''error dot txt file.'''
  
 
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| Now, Click on '''Save''' and switch to the '''terminal'''.
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| Now, click on '''Save''' and switch to the '''terminal'''.
  
 
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|* Redirection and file descriptors  
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|* '''Redirection''' and '''file descriptors'''
  
 
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| 08:38
 
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|* Standard input using <(less than) symbol
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|* '''standard input''' using '<' (less than) symbol
  
 
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| 08:42
 
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|* Standard output using  >(greater than) symbol
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|* '''standard output''' using  '>' (greater than) symbol
  
 
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|* Standard error using 2> (2 greater than symbol).
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|* '''standard error''' using '2>' (2 greater than symbol).
  
 
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| Write a program in any language like C, C++, Java.
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| write a program in any language like C, C++, Java  
  
 
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| 08:59
 
| 08:59
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| And '''redirect''' the '''output''' or '''error''' to a new file.
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| and '''redirect''' the '''output''' or '''error''' to a new file.
  
 
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| 09:04
 
| 09:04
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| Or, create a '''text file''' with some content like your name, address.
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| Or, create a '''text file''' with some contents like your name, address.
  
 
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| 09:11
 
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| '''Redirect''' the content to a new file.
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| '''Redirect''' the contents to a new file.
  
 
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|  Conducts workshops using spoken tutorials.
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|* Conducts workshops using spoken tutorials.
  
 
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| 09:34
 
| 09:34
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|  Gives certificates to those who pass an online test.
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|* Gives certificates to those who pass an online test.
  
 
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| The '''script''' has been contributed by FOSSEE and Spoken-Tutorial teams.
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| 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.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14

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