View source for Linux-New/C3/Text-Editing-using-sed/English

 '''Title of script''': ''' Text Editing using sed'''
'''Author: EduPyramids'''
'''Keywords: sed, substitute, insert, delete, global substitution, g flag, case-insensitive, context addressing, Video Tutorial.'''



{| border=1
| | '''Visual Cue'''
| | '''Narration'''
|- 
|| '''Slide 1'''
'''Title Slide'''
|| Welcome to this spoken tutorial on '''Text Editing using sed'''.
|- 
|| '''Slide 2 Learning Objectives'''
|| In this tutorial, we will learn to:* Perform text substitution using '''sed '''command.
* Use the '''g''' flag for global substitution.
* Execute multiple '''sed''' commands using the '''hyphen e''' option.
* Apply substitution based on context.
* Insert and remove lines from a file.
* Redirect '''sed '''output to an output file.


|- 
|| '''Slide 3'''
'''System Requirements'''
|| To record this tutorial, I am using* '''Ubuntu OS '''version 24 point 04
* '''Bash''' version 5 point 1 point 16;
|- 
|| '''Slide 4 Pre-requisites'''
https://EduPyramids.org
|| Learners should have* '''Ubuntu version 24 point 04 '''and
* '''Bash version 5 '''point '''1 '''point '''16'''
* 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.
|- 
|| 
| | Let us run some examples of sed commands using the terminal.
|- 
|| Type
'''cat seddemo.txtpress Enter'''
Highlight the word kumar in the lines.Point to the fourth and sixth lines
|| Let us first view the contents of the file '''sed demo dot t x t.'''
Notice the word '''Kumar'''.
It appears twice in the fourth line and once in the sixth line.
|- 
|| Type
'''sed 's/[kK]umar/Roy/' seddemo.txt'''
|| Let’s suppose we want to substitute '''Kumar''' with '''Roy.'''
Type the following command and press '''Enter'''.
|- 
|| Highlight one by one
'''sed'''
'''s'''
'''[kK]umar'''
'''Roy'''
'''forward slashes'''
'''seddemo.txt'''
|| Let us understand this command.

'''sed''' is the stream editor.
The letter '''s''' stands for substitution.
This pattern matches bothuppercase '''Kumar''' and lowercase '''kumar'''.
The word '''Roy''' is the replacement text.
The forward slashes separate the pattern and the replacement.
The file '''sed demo dot txt''' is the input file.
|- 
|| Press '''Enter'''.
Show the output on the terminal
|| 
In the output, the word '''Kumar''' is replaced with '''Roy'''.
|- 
|| 
Show the output on the terminal and the file '''seddemo.txt''' opened next to it
Highlight 4th line of both output and in the file
|| But only the first occurrence of the word '''Kumar''' is replaced in each line.
This happens because, by default, '''sed''' substitutes only the first match in a line.
Note the substitution happens only on the terminal output.
The original file '''sed demo dot t x t '''is not modified.
|- 
|| '''Slide 6'''

'''Global Substitution'''
* '''By default, sed replaces only the first match in each line.'''
* '''To replace all occurrences in a line, we use the g flag.'''
* '''The letter g stands for global substitution.'''
* '''When the g flag is used, sed searches the entire line for matches.'''
* '''Every matching pattern in that line is replaced.'''
* '''The g flag is written after the substitution command.'''
'''General syntax:'''
'''sed 's/pattern/replacement/g' filename'''
|| * By default, '''sed''' replaces only the first match in each line.
* To replace all occurrences in a line, we use the '''g''' flag.
* The letter '''g''' stands for global substitution.
* When the '''g''' flag is used, '''sed''' searches the entire line for matches.
* Every matching pattern in that line is replaced.
* The '''g''' flag is written after the substitution command.
This is the general syntax.
|- 
|| Type
'''sed 's/[kK]umar/Roy/g' seddemo.txt'''
'''Press Enter'''

'''Highlight the output'''
|| Type this command and press '''Enter.'''
Output shows, both occurrences in the fourth line are replaced.
|- 
|| Type
'''sed 's/kumar/Roy/Ig' seddemo.txt'''
=== and press Enter.Case-insensitive matching ===
|| Type the following command and press '''Enter.'''
Instead of specifying lowercase and uppercase letters using brackets, we can use the '''I option'''.
The '''I''' option makes the pattern match '''case insensitive'''.
Observe that the output is the same as the previous command.
Both methods can be used to produce the same result.
|- 
|| '''Slide 7'''
'''Multiple Substitutions using -e'''
* sed allows performing more than one operation in a single command.
* The -e option is used to specify multiple sed expressions.
* Each -e represents one sed command.
* Commands are executed in the order they are written.
* This is useful when multiple substitutions are required on the same input.



|| * '''sed '''allows performing more than one operation in a single command.
* The '''hyphen e '''option is used to specify multiple '''sed''' expressions.
* Each '''hyphen e '''represents one '''sed '''command.
* Commands are executed in the order they are written.
* This is useful when multiple substitutions are required on the same input.
|- 
|| 
|| Let us see how to replace '''electronics''' with '''electrical '''and '''civil''' with '''metallurgy.'''
|- 
|| Type
'''sed -e 's/electronics/electrical/g' -e 's/civil/metallurgy/g' seddemo.txt'''
|  | Type this command.
|- 
|| 
|| Let us understand this code.
* '''hyphen e''' allows using more than one '''sed''' command in a single line.
* '''s slash electronics slash electrical slash g '''replaces all occurrences of '''electronics''' with '''electrical.'''
* '''s slash civil slash metallurgy slash g '''replaces all occurrences of '''civil'''with '''metallurgy.'''

|- 
|| press '''Enter'''

Highlight the replaced words in the output
|| Now, press '''Enter'''.
Observe that words are replaced.
|- 
|  | '''Context-Based Substitution'''
|| Let’s change the '''stream''' of '''Anirban '''from '''computers''' to '''mathematics'''.
|- 
|| Type
'''sed '/Anirban/s/computers/mathematics/g' seddemo.txt'''
|| Type this command and press '''Enter'''.
Observe that computers is changed to mathematics.
|- 
|  | '''Deleting Lines using sed'''
|| Let us see how to remove all lines containing the word '''electronics'''.
In other words, select those lines which do not have an electronics stream.
|- 
|| Type

'''sed '/electronics/d' seddemo.txt > nonElectronics.txt'''
|  | Type this command.
|- 
|| 
'''Highlight'''
'''/electronics/'''
'''d'''
'''seddemo.txt'''
'''>'''
'''nonElectronics.txt'''
|| Here, '''slash electronics slash''' is a context address that matches lines containing electronics.
'''d '''means deletes the matched lines
'''seddemo dot t x t '''is the input file.
greater than means redirects output to a file
'''non Electronics dot t x t''' is the output file.
Press '''Enter'''.
|- 
|| '''Type cat nonElectronics.txt'''
'''press Enter'''
'''Show the output'''
|| Let us view the contents of the new file '''nonElectronics'''.
The file shows only those records that are not in the electronics stream.
You may wonder why substitutions are not reflected in the text file.
This is because all substitution results are displayed only on the terminal.
The original text file is not modified unless explicitly instructed.
|- 
|  | '''Inserting Lines Using sed'''
|  | Suppose we want to insert a line at the beginning of the file.
|- 
|| Type
'''sed '1i Student Information' seddemo.txt'''
|  | Type this command.
|- 
|| Highlight one by one
'''1'''
'''i'''
'''Student Information'''
|| Here:
• 1 is the line number• i is the insert command
• '''Student Information '''is the text to be inserted
|- 
|| Press Enter.
Highlight the line:
'''Student Information'''
|| Press '''Enter.'''
Output shows the line '''Student Information''' inserted at the beginning of the file.
|- 
|  | '''Inserting Multiple Lines'''
|| Let us see how to insert more than one line in the file '''seddemo dot t x t'''.
'''Student Information''' in the first line and '''2026''' in the next line.
|- 
|| Type
'''sed '1i Student Information\n2026\nRecords' seddemo.txtpress Enter'''
|| Now let us type this command.
Press '''Enter.'''
|- 
|| Point to '''\n'''
|| Notice '''backslash n '''between the string '''Information''' and '''2026'''.
'''backslash n '''moves to a new line and prints '''2026 '''in the next line after '''Student Information'''.
Similarly after 2026, new string '''Records''' is printed in the third line.
|- 
|| '''Slide 8'''
'''Summary'''
In this tutorial, we have learnt to:
* Perform text substitution using '''sed '''command
* Use the '''g''' flag for global substitution
* Execute multiple '''sed''' commands using the '''-e''' option
* Apply substitution based on context

* Insert and remove lines from a file
* Redirect '''sed '''output to an output file
|| With this we come to the end of this tutorial.
Let us summarise.
|- 
|| '''Slide 9'''
As an assignment please do the following:* Using '''sed '''and the file '''seddemo.txt''', replace the word '''computers''' with '''computer-science'''.
* Replace '''electronics''' with '''ece''' in all occurrences.
* Perform both substitutions in a single command using the '''-e option'''.
* Delete all lines that belong to the '''civil''' department.
# 
|  | As an assignment, please do the following.
|- 
|| '''Slide 10 
Thank you'''
|| This Spoken Tutorial is brought to you by EduPyramids Educational Services Private Limited SINE IIT Bombay.Thank you.
|-
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