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

 

 

 

 

{| border=1

|''' Visual Cue'''

| Dear friends, welcome to the spoken tutorial on''' Basics of redirection'''

| In this tutorial, we will learn

|Input and output in '''Bash'''

| Redirection and file descriptors  

|Standard input

 

| Standard output

| Standard error

 

|With the help of some examples  

| To follow this tutorial you should have knowledge of '''Shell Scripting''' in''' BASH.'''

|If not, for relevant tutorials please visit our website which is as shown,'''(http://www.spoken-tutorial.org)'''

| For this tutorial I am using

| '''Ubuntu Linux''' 12.04 '''Operating System''' and

| '''GNU BASH''' version 4.2

|Please note,''' GNU Bash''' '''version 4''' or above is recommended for practice.

| In '''GNU/Linux '''we can send output to a file or read input from a file.

| Each '''Shell''' command has its own inputs and outputs

|Input and output is redirected using a special notation interpreted by the '''Shell'''

|  Changing the default path of input or output is called as''' redirection'''

| In GNU/Linux everything is a file, including the hardware

| '''0''' for '''Input''' i.e. '''Keyboard'''  

| '''1''' for '''Output''' i.e. '''Screen '''

| '''2 '''for '''Error '''i.e. '''Screen '''

 

 

 

|''0, 1, 2 '''are '''POSIX '''numbers and also known as '''file descriptors''' '''(FD''').  

| A redirector uses '''POSIX''' numbers to talk with a user or other program.  

|  Standard input: Standard input is the default input method

|  Also known as '''stdinb(Standard input). '''

|  The default standard input is the keyboard.  

|   '''Less than '''symbol is input redirection symbol

|  The syntax is '''Command space less than symbol space filename'''

 

| Let me open a file named '''redirection dot sh'''

|  Type''' sort space less than symbol space file dot txt''

| This is an example of input redirection.

|-

| The input is taken from file '''file dot txt'''

|  '''sort '''command does the '''sorting '''of numbers present in ''' file dot txt'''

|Click on '''Save'''  

| Let us run the file ''' redirection dot sh'''  

| Open the '''terminal''' using '''Ctrl, Alt''' and '''T''' simultaneously on your keyboard.

| Before that, let us see the content of '''file dot txt'''

| Type '''cat space file dot txt'''.

|Press Enter

|You can see that the file contains series of numbers

| Now type: '''chmod space plus x space redirection dot sh'''

| Type '''dot slash redirection dot sh'''

 

| We can see the output on the '''terminal''' after sorting.

| Come back to our slides.

| Standard output: Standard output is used by all commands to display output.  

|  The default output is displayed on the screen.  

|  ( > )'''Greater than''' symbol is the output redirection symbol  

|  Syntax is '''Command space greater symbol space filename'''

| Let me go back to a file '''redirection dot sh'''

| Comment the previous line ie. '''sort'''

| Below it, type ''' ls space greater than space ls underscore file.txt'''

| This is an example of output redirection.

| The output of ''''ls'''' will be stored in '''ls_file dot txt '''.

| '''ls '''command lists the information about files in that particular directory.

|Now, save the file and switch to the '''terminal'''

| Let me clear the prompt.  First let us type ''''ls'''' and see the output.

| Now press the '''uparrow''' key thrice.

| Now let us check whether the output is redirected correctly.

| Type '''gedit space ls underscore file dot txt '''and press '''Enter.'''

| We can now see the output in this file. So our redirect was successful.

| Come back to our slides.   

|  '''Standard error '''is the default output error  

|  It is used to write all system errors  

|  '''Two greater than symbol (2>)''' is error redirection symbol  

| Syntax is '''command space 2 greater than space error dot txt'''

| Let me go back to the file '''redirection dot sh'''

| We will comment the previous line. i.e.'''ls'''

| Below it type ''' rm space backslash tmp backslash 4815 dot txt space 2 greater than symbol space error dot txt.'''

 

| The error output is redirected to '''error dot txt file.'''

| Now, Click on '''Save''' and switch to the '''terminal'''.

| Type '''rm space backslash tmp backslash 4815 dot txt'''

| The error displayed is

| '''rm: cannot remove slash tmp slash 4815 dot txt: No such file or directory'''

 

| Now we will execute our file.

|  Press the '''uparrow''' key.

| And, Recall the previous command '''dot slash redirection dot sh'''

| Now let us check whether the error is redirected.

| Type '''gedit space error dot txt''' and press '''Enter.'''

 

| We can now see the error redirected to file '''error dot txt'''.

| Let us summarise.  

| In this tutorial we learnt

| Input and output in Bash

| Redirection and file descriptors  

| Standard input using <(less than) symbol

| Standard output using  >(greater than) symbol

| Standard error using 2> (2 greater than symbol)

| As an assignment,

| Write a program in any language like C, C++, Java.

| And redirect the output or error to a new file.

| Or, create a text file with some content like your name, address.

| Redirect the content to a new file.

| It summarises the Spoken Tutorial project.

| The Spoken Tutorial Project Team

| Conducts workshops using spoken tutorials

| Gives certificates to those who pass an online test

| Spoken Tutorial Project is a part of the Talk to a Teacher project.

 

| More information on this Mission is available at the link shown below.  

| This is Ashwini from IIT Bombay. Signing off. Thank you for joining