Nancyvarkey at 08:22, 3 March 2021

2021-03-03T08:22:59Z

Nirmala Venkat at 06:14, 2 March 2021

2021-03-02T06:14:59Z

Nancyvarkey at 07:55, 1 March 2021

2021-03-01T07:55:15Z

Nirmala Venkat: Created page with " {| border="1" |- || '''VISUAL CUE''' || '''NARRATION''' |- || '''Slide 1:''' || Welcome to the '''spoken tutorial '''on '''Sed substitute''' command. |- || '''Slide 2:''' ''..."

2021-02-25T12:27:56Z

Created page with " {| border="1" |- || '''VISUAL CUE''' || '''NARRATION''' |- || '''Slide 1:''' || Welcome to the '''spoken tutorial '''on '''Sed substitute''' command. |- || '''Slide 2:''' ''..."

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{| border="1"
|-
|| '''VISUAL CUE'''
|| '''NARRATION'''
|-
|| '''Slide 1:'''
|| Welcome to the '''spoken tutorial '''on '''Sed substitute''' command.
|-
|| '''Slide 2:'''

'''Learning Objectives'''
|| In this tutorial, we will learn about:
* Workflow of '''Sed''' command
* Introduction to '''Sed''' command
* '''Sed''' '''substitute''' command
|-
|| '''Slide 3:'''

'''System requirements'''
|| This tutorial is recorded using
* '''Ubuntu Linux '''OS version 18.04
|-
|| '''Slide 4:'''

'''Prerequisites'''
||To follow this tutorial,you should know
* Basics of Linux.

If not, then go through the Linux spoken tutorials on this website.
|-
|| Slide 5:

Code files
||
* The files used in this tutorial are available in the '''Code Files '''link on this tutorial page.
* Please download and extract them
* Make a copy and then use them while practising

|-
||'''Slide 4:Workflow of SED commands'''

1. '''Read''' - '''Sed''' reads a line from the input stream.

It can be a file or standard input.

It is stored in an internal buffer called '''pattern buffer'''.
|| '''Sed''' follows a simple workflow:

First''' Sed''' reads a line from the input stream.

It can be a file or standard input.

It is stored in an internal buffer called '''pattern buffer'''.

|-
|| '''Slide 4(a):'''

2. '''Execute''' – All '''Sed''' commands are executed sequentially on the pattern buffer.

3. '''Display-''' Sends the modified content to the output stream.

The pattern buffer will be empty after sending the data.
|| Second step is '''Execute'''.

All '''Sed''' commands are executed sequentially on the pattern buffer.

Third step is '''Display.'''

It sends the modified content to the output stream.

The pattern buffer will be empty after sending the data.
|-
|| Open the terminal
|| Open the terminal by pressing '''Ctrl+Alt+T '''keys simultaneously.

Remember to press the '''Enter''' Key after every command.
|-
||
|| First let us see how to use the '''Sed''' command with standard input.
|-
||

'''sed ‘s/Unix/Linux/’'''
'''Highlight according to narration'''

Type

Unix is the most powerful OS

Highlight the output

Press Ctrl+d
||Type,

'''sed''' space within single quotes '''s forward slash Unix forward slash Linux forward slash'''

Here ‘s’ indicates the '''substitute''' option.

'''substitute''' command will replace '''Unix''' with '''Linux'''.

'''Sed''' command is mostly used to replace the text in a file.

Here we are using the '''Sed''' command without a file.

So it will process from standard input.

Type '''Unix is the most powerful OS '''and press Enter

We can see the '''Unix''' word is replaced with '''Linux'''.

Press “Ctrl+d” key to terminate the standard input.
|-
|| '''sed ‘s/Unix/Linux/’'''

'''>“unix is the most powerful OS” '''

Highlight the small u in unix.

Press “Ctrl+d
||Let us execute the same command again.

Type '''unix is the most powerful OS''' and press Enter.

Note that we have typed ‘u’ in lower case in unix.

Here the replacement didn’t take place.

This is because sed commands are case sensitive.

Press “Ctrl+d” keys to return back to the command prompt.
|-
|| '''cd Downloads'''

'''../Downloads>cat message.txt'''

'''Highlight Downloads'''

'''Highlight message.txt'''
|| I have saved a file '''message.txt '''in my downloads folder.

Go to the directory where you have''' '''saved the '''message.txt''' on your system.

Let us see the content of '''message.txt '''

Type '''cat space message.txt '''

I’ll be using this file for demonstration of sed commands.

Clear the screen.
|-
|| '''>sed ‘’ message.txt'''
|| Let us read the content of the file '''message.txt '''using '''Sed'''.

Type '''sed space a pair of single quotes space message.txt'''
|-
|| Highlight according to narration

|| Look at the output.

It prints the content of the entire file.

A pair of single quotes implies the '''Sed''' option.

In our case there is no '''Sed''' option.

So it prints the contents of the pattern buffer on the standard output.
|-
||'''Slide 6: Syntax:'''

'''sed [options]...[command] [File]'''

'''Example: '''

'''sed G message.txt'''
|| The general syntax for '''Sed''' command is given here:

In this example, capital ‘'''G’ '''is the option to add line space to the file.

'''message.txt '''is the file where the sed command will work with.

If no filename is provided with '''Sed '''command, then the command will work on standard input data.
|-
||

> '''sed G message.txt'''

'''Highlight the output'''
||Let us execute the command and check the output.

Type '''sed space G space message.txt '''

We can observe line space is added to the output.
|-
||
|| Next let us see about the substitute command.
|-
|| '''Slide 7:'''

'''Substitute command'''

'''syntax:'''

'''sed ‘s/oldstring/newstring/’ file'''

'''sed ‘s/oldstring/newstring/’ file > output.txt'''
||

Here ‘s’ specifies the substitute command.

forward slash (/) is to delimit the two arguments.

'''oldstring''' is the string to be searched from the file.

'''newstring''' is the string to be replaced by the searched string.

'''file''' is the input text file.

The redirection symbol and a file name is used to redirect the output to another file.

By default sed outputs everything to standard output instead of saving it in a file.
|-
||
|| Switch back to terminal.
|-
||'''>sed s/success/victory/ message.txt'''

'''Highlight where the replacement has not taken place'''
||Type

'''sed space s forward slash success forward slash victory forward slash space message.txt'''

This will replace the word success with the word victory in message.txt

We can use '''sed''' commands without using single quotes.

Note that the word '''success''' has been replaced with the word '''victory''' in a few places.

I’ll explain later why the replacement didn’t take place in the entire file.
|-
||

'''>sed s/success/great victory/ message.txt'''

'''>sed ‘s/success/great victory/’ message.txt'''

'''Highlight great victory'''

||Now let us try this command with space in the string.

Here we got an error and we didn’t get the expected output.

Try the same command with single quotes as shown.

So quotes are needed when we use space or a special shell character inside the command.

It is good practice to write sed commands using quotes.
|-
||Highlight according to narration

>'''sed ‘s/success/victory/’ message.txt'''
|| Let us see the various options with the substitute command.

Type the command as shown.

Note that this has changed '''success''' to '''victory''' once on each line.

Sed replaces only the first match in each line with the substitute command.

The last sentence has '''success''' twice. But it has changed only at one place.

It will not replace the second or third occurrence in the same line.

Also note that in certain lines it didn’t substitute with the word victory.

This is because '''Success''' word has capital ‘S’.

As we know, '''sed''' commands are case sensitive.
|-
|| >'''sed ‘s/success/victory/ I’ message.txt'''
|| Type the command as shown.

We can use the flag capital '''I''' to make the pattern match case insensitive.

Look at the output.
|-
|| '''>sed ‘s/success/victory/ 2’ message.txt'''

Highlight the last sentence
|| If you want to replace the 2nd occurrence in a line, use 2 as a flag as shown.

'''>sed ‘s/success/victory/ 2’ message.txt'''
|-
|| >'''sed ‘s/success/victory/’ message.txt'''
|| What if we want to replace all the instances of matches in a file?

Use the ‘g’ option to represent global replacement.
|-
|| '''>sed ‘s/success/victory/ Ig’ message.txt'''
|| Next we will see how to replace from nth occurrence to all the occurrences in a line.

Type the command as shown.

Here, we have used the capital '''I''' and '''g''' flags together.

This will replace all the patterns globally with case insensitive.
|-
|| '''> cat message.txt'''

'''Highlight ‘Albert’ at two places'''

'''>sed '/Albert/s/success/victory/' message.txt'''

|| Let us see another example.

We want to replace the word success with victory in the line which contains the text '''‘Albert’'''.

Type the command as shown.

Let us check the output.
|-
||
|| Let us see how the regular expression is used in substitute command.
|-
||'''> sed ‘s/[0-9]*//’ message.txt'''

Highlight the output
|| Type,

'''sed within single quotes s forward slash within square brackets 0 hyphen 9 asterisk forward slash forward slash space message.txt'''

Here regular expression represents one or more occurrences of 0-9 characters.

I want to replace it with the empty string.

In the output we can see, all the line numbers are replaced with empty spaces.
|-
|| '''> sed ‘1,2 s/success/victory/g’ message.txt'''
|| We can also perform the substitute command on specific lines.

Type the command as shown.

We can see the replacement in the first two lines
|-
|| '''> sed ‘4,$ s/success/victory/g’ message.txt'''
||In this command, $ represents the last line.

Here, replacement takes place from the fourth line to the last line.
|-
|| '''>> sed ‘/^2./ s/success/victory/’ message.txt'''
||We can select a particular line with the regular expressions to perform the substitute command.

For example, in this command caret (^)symbol represents the beginning of the line.

If the line begins with 2 dot, then on that line it will perform the substitute command.
|-
||
|| With this we come to the end of this tutorial. Let us summarize.
|-
||

Slide 8:

Summary
|| In this tutorial, we learnt
* Work flow of '''Sed''' command
* Introduction to '''Sed''' command
* '''Sed''' '''substitute''' command
|-
|| Slide:9

Assignment
|| As an assignment, try the below commands and see the output.

# sed 's/[0-9.]*/(*)/' message.txt
# sed '/secrets/s/success/victory/g' message.txt
# sed 's/-/:/' message.txt

|-
|| Slide 10:

(About Spoken Tutorial Project)
|| The video at the following link, summarizes the''' Spoken Tutorial '''project.

Please download and watch it.
|-
|| Slide 11:

(About Spoken Tutorial Project)
|| The '''Spoken Tutorial''' Project Team conducts workshops and gives certificates.

For more details, please write to us.
|-
|| Slide

Forum questions:
||
* Do you have questions in THIS Spoken Tutorial?
* Please visit this site
* Choose the minute and second where you have the question
* Explain your question briefly
* The Spoken Tutorial project team will ensure an answer
* You will have to register on this website to ask questions.

|-
|| '''Slide: '''Forum for specific  Questions

|| * The Spoken Tutorial forum is for specific questions on this tutorial.
* Please do not post unrelated and general questions on them.
* This will help reduce the clutter.
* With less clutter, we can use these discussions as instructional material.

|-
|| '''Slide: '''Acknowledgement

|| Spoken Tutorial project is funded by the Ministry of Education (MoE), Govt. of India.
|-
||
|| This is Pooja from Spoken Tutorial Project, IIT Bombay signing off.
Thanks for joining.
|-
|}

@@ Line 81: / Line 81: @@
 ||
-'''sed ‘s/Unix/Linux/’'''
+'''sed ‘s/Unix/Linux/’'''  >> Enter
 '''Highlight according to narration'''
 ||Type,
-'''sed space''' within single quotes '''s forward slash Unix forward slash Linux forward slash'''  >> Enter
+'''sed space''' within single quotes '''s forward slash Unix forward slash Linux forward slash'''
 Here '''‘s’''' indicates the '''substitute''' option.
@@ Line 115: / Line 117: @@
 ||Press '''“Ctrl+D”''' keys to terminate the standard input.
 |-
-|| '''sed ‘s/Unix/Linux/’'''
+|| '''sed ‘s/Unix/Linux/’''' >> Enter
-'''>“unix is the most powerful OS” '''
+'''>“unix is the most powerful OS” ''' >> Enter
 ||Let us execute the same '''command''' again.
-Type '''unix is the most powerful OS''' and press '''Enter'''.
+Type '''unix is the most powerful OS'''.
 Note that we have typed '''‘u’''' in lowercase in '''Unix'''.
@@ Line 298: / Line 300: @@
 ||Highlight the word '''Success''' in the output.
-Also note that in certain lines it didn’t substitute with the word '''victory'''.
+||Also note that in certain lines it didn’t substitute with the word '''victory'''.
 This is because '''Success''' word has capital ‘S’.

@@ Line 188: / Line 188: @@
 In this example, capital ‘'''G’ '''is the option to add '''line space''' to the file.
-'''message.txt '''is the file where the '''sed command''' will work with.
+'''message.txt '''is the file which the '''sed command''' will work with.
 If no filename is provided with '''sed command''', then the '''command''' will work on standard input data.

Sed-Stream-Editor/C2/Sed-substitute-command/English - Revision history

Nancyvarkey at 08:22, 3 March 2021

Nirmala Venkat at 06:14, 2 March 2021

Nancyvarkey at 07:55, 1 March 2021

Nirmala Venkat: Created page with " {| border="1" |- || '''VISUAL CUE''' || '''NARRATION''' |- || '''Slide 1:''' || Welcome to the '''spoken tutorial '''on '''Sed substitute''' command. |- || '''Slide 2:''' ''..."