BASH/C3/Basics-of-Redirection-(error-handling)/English-timed
From Script | Spoken-Tutorial
| 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 standard output |
| 00:18 | standard errorwith 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. |
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| 09:23 | If you do not have good bandwidth, you can download and watch it. |
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| 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. |
