View source for Linux-Ubuntu/C3/Introduction-to-the-Stream-Editor-sed/English

'''Title of script''': '''Introduction to the Stream Editor sed.'''

'''Author: EduPyramids.'''

'''Keywords: stream editor, sed, display, substitute, insert, delete, context addressing, Line addressing, edupyramids, video tutorial.'''

{|border=1
|- 
|| '''Visual Cue'''
|| '''Narration'''
|- 
|| '''Slide 1'''

'''Title Slide'''
|| Welcome to this spoken tutorial on '''Introduction to the Stream Editor sed'''.
|- 
|| '''Slide 2'''

'''Learning Objectives'''
|| In this tutorial, we will learn to:
* Use '''sed''' as a stream editor to process text.
* Print specific lines from a file.
* Apply line-based addressing techniques.
* Use context-based addressing with pattern matching.
* Redirect matched output to files.
|- 
|| '''Slide 3'''

'''System Requirements'''
|| To record this tutorial, I am using
* '''Ubuntu OS '''version 24 point 04 and
* '''Bash''' version 5 point 1 point 16.
|- 
|| '''Slide 4'''

'''Pre-requisites'''

[https://EduPyramids.org/ https://EduPyramids.org] 
|| To follow this tutorial,
* Learners should have '''Ubuntu '''version''' 24 point 04.'''
* '''Bash''' version 5 point 1 point 16 and
* Should know the basics of '''Linux''' terminal.
* For the prerequisite '''Linux''' tutorials please visit this website.
|- 
|| '''Slide 5'''

'''Code Files'''

The following code files are required to practice this tutorial.
# '''seddemo.txt.'''
# '''sed-commands.txt'''

These files are provided in the Code Files link of this tutorial page.
|| 
* The following code files are required to practice this tutorial.
* These files are provided in the Code Files link of this tutorial page.
|- 
|| '''Slide 6'''

'''Introduction to sed'''
|| 
* '''sed''' is one of the most versatile tools available in Linux.
* It is a '''stream''' '''editor''' used to process text line by line.
* '''sed '''can function both as a display tool and an editing tool.
* It supports editing operations such as insertion, substitution and deletion.
* By default, '''sed '''sends its output to the standard output.
* The original file remains unchanged unless '''sed''' is explicitly instructed to modify it.
|- 
|| Open the file '''seddemo.txt'''

Highlight the lines, marks and student details.
|| Let us start with a few examples.

We will see how to print lines using the '''sed''' command.

I have a file called '''sed demo dot t x t''' in the home directory.

This file is provided in the code files folder. Please download it and move it to your Home directory.

Let us view its contents.

This file contains entries such as roll no, name, stream, marks, result and the stipend amount.
|- 
|| Press '''Ctrl + Alt + T keys.'''
|| Let us open the terminal.
|- 
|| Type:'''sed '2p' seddemo.txt''' 
|| Let’s print the second line of the file.

Type,

'''sed space single quote 2 p single quote space sed demo dot t x t'''.
|- 
|| '''Highlight 2'''

'''Highlight p'''

Press '''Enter'''

highlight the output.

Hover your mouse on the second line of the output
|| Here, '''2''' specifies the location, which is the second line.The letter '''p''' specifies the action, which is printing.

Press '''Enter'''.

Observe the output.

It shows the entire file but the second line appears twice.

This is the default behavior of '''sed'''.

'''sed''' prints every line by default

The '''p''' option prints the specified line again.
|- 
|| At the prompt type:

'''sed -n '2p' seddemo.txt '''Press''' Enter'''
|| To print only the second line, type this command and press''' Enter.'''
|- 
|| '''Highlight -n'''

'''Highlight 2'''

'''Highlight p'''

'''Highlight sed demo.txt'''
|| Observe that only the second line is printed.
* The '''hyphen n '''option suppresses the default output of sed.
* '''2''' specifies the line number to display or edit.
* '''p''' specifies the action to perform.
* It tells '''sed''' to print the selected line.
* '''sed demo dot t x t''' specifies the input file name.

This is the general syntax of the '''sed''' command. 
|- 
|| At the prompt type:'''sed -n '$p' seddemo.txt''' Press''' Enter.'''

'''Highlight -n'''

'''Highlight $ sign'''
|| Now let us print the last line.Type this command and''' '''press '''Enter'''. We see that the last line is displayed.

The '''hyphen n''' suppresses automatic printing of all lines.

Dollar refers to the last line of the file.
|- 
|| At the prompt

'''sed -n '3,6p' seddemo.txt '''press''' Enter'''

'''Highlight the output'''
|| Let us just print the entries from the third line to the sixth line of the file.

Type this command and''' '''press '''Enter'''.

The output displays the lines from the third line to the sixth line.
|- 
|| Type'''sed -n '3,6!p' seddemo.txt'''

Press''' Enter'''

'''Show the file on one side and the output comparison'''
|| If we want to print all lines except the third to the sixth lines.

Type this command.Any action can be reversed by placing an exclamation mark before the command.

This allows us to select the complementary set of lines.

Press '''Enter'''.

The output displays all lines except lines 3 to 6.
|- 
|| 
|| So far, we have specified the lines in a file on which an action applies.

This method is known as '''line addressing.'''
|- 
|| '''Slide 7'''

'''Line addressing'''
|| Line addressing identifies lines using their position in the file.

It is one way to select specific lines for an action.

Another method is called '''context addressing'''.
|- 
|| '''Slide 8'''

'''Context''' '''addressing'''
|| 
* '''Context''' '''addressing''' selects lines based on their content.
* Lines are matched using a word, string, or pattern.
* Only the lines that match the pattern are processed.
* It is useful when line numbers are unknown or variable.
* Regular expressions can be used for flexible and powerful matching.
* Commonly used for searching and filtering text in files.
|- 
|| 
|| Let us see an example.
|- 
|| Highlight the lines with word computers in the text editor- show the text file '''seddemo.txt'''.

At the prompt'''sed -n '/[cC]omputers/p' seddemo.txt'''

Highlight '''-n'''

highlight '''/[cC]omputers/'''

'''highlight p'''

Press Enter.

highlight '''/[cC]omputers/'''
|| Suppose we want to print the lines containing the word '''computers'''.

Go to the Terminal.

Type the following command.

'''hyphen n '''suppresses default output.

This is the '''Context address'''. 

It matches lines containing the word computers with small c and capital C.

'''p,''' prints the matched lines.

Press '''Enter'''.

Observe the output.

The lines containing the word '''computers''' are displayed.

We enclose parts of the pattern within square brackets.

This allows us to match any one character present inside the brackets.

When using a pattern in '''sed''', it must be written '''between forward slashes.''' 
|- 
|| Type the command:

'''sed -n '/[cC]omputers/w computer-student' seddemo.txt'''

press '''Enter.'''

'''Open file and show the computer-student '''
|| Let us now see how to write the matched output to a file using the '''w''' option.

Type the following command.

and Press '''Enter'''.

Output is redirected to a file instead of getting displayed on the terminal.

This is useful for extracting specific lines into a separate file.

All matching lines are saved in the file '''computer hyphen student. '''
|- 
|| Type

'''cat computer-student '''andPress '''Enter'''
|| Let us view the content of the '''computer hyphen student '''file. 

type '''cat''' '''space''' '''computer hyphen student''' and press''' Enter.'''

We see that lines that match the given pattern are in the file.
|- 
|| Type the following command.'''sed -n -e '/electronics/w electro' -e '/civil/w civil' seddemo.txt'''Press '''Enter'''

'''Highlight -e'''

'''Highlight /electronics/w electro'''

'''Highlight /civil/w civil'''

Show the two files created
|| Let us see how we can use '''multiple sed expressions''' in a single command. This allows us to write different matched lines to separate files.

Type this command and press '''Enter.'''

The '''hyphen e''' option allows combining multiple sed commands in a single line.

'''slash electronics slash w''' '''electro '''writes lines matching electronics to '''electro '''file.

'''slash civil slash w civil''' writes lines matching civil to '''civil '''file.

After running the command, two text files, '''electro''' and '''civil''', are created with the matched lines.
|- 
|| '''cat electro '''Press Enter

Highlight the contents

'''cat civil'''

Press Enter

Highlight the contents
|| To see what they contain, type '''cat space''' '''electro '''and press''' Enter.'''

This displays the entries with the word '''electronics'''.

Let us see the contents of the file '''civil '''

Type '''cat space''' '''civil '''and press''' Enter.'''

This displays the entries having the word '''civil'''.
|- 
|| 
|| We will see more sed commands in the upcoming tutorial.
|- 
|| '''Slide 9'''

'''Summary'''

In this tutorial, we have learnt to:
* Use '''sed''' as a stream editor to process text
* Print specific lines from a file
* Apply line-based addressing techniques
* Use context-based addressing with pattern matching
* Redirect matched output to files
|| With this we come to the end of this tutorial.

Let us summarise.
|- 
|| '''Slide 10'''

'''Assignment '''

As an assignment,

Using the text file '''seddemo.txt,'''
# Print only the first five lines of the file.
# Print all lines that do not contain the word "failed".
# Write all lines containing the word student into a file named '''student-list.txt.'''
|| As an assignment, please do the following.
|- 
|| '''Slide 11'''

'''Thank you'''

|| This Spoken Tutorial is brought to you by '''EduPyramids''' Educational Services Private Limited SINE IIT Bombay.

Thank you.
|-
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