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

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, sed space within single quotes s forward slash Unix forward slash Linux forward slash >> Enter Here ‘s’ indicates the substitute option. substitute command will replace Unix with Linux.
Highlight sed	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" >> Enter Highlight the output Press Ctrl+d	Type Unix is the most powerful OS and press Enter We can see the word Unix is replaced with Linux.
Press “Ctrl+D” keys	Press “Ctrl+D” keys to terminate the standard input.
sed ‘s/Unix/Linux/’ >“unix is the most powerful OS”	Let us execute the same command again. Type unix is the most powerful OS and press Enter. Note that we have typed ‘u’ in lowercase in Unix. Here the replacement didn’t take place.
Highlight "unix">> the small u in unix. Press “Ctrl+D" keys	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.
Type cat space message.txt >> Enter	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 >> Enter	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.
Highlight the pair of single quotes	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 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 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	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.
Highlight the word victory in the output.	Note that the word success has been replaced with the word victory in a few places.
Highlight the word success in the output.	I’ll explain later why the replacement didn’t take place in the entire file.
>sed s/success/great victory/ message.txt	Now let us try this command with space in the string. Here we got an error and we didn’t get the expected output.
>sed ‘s/success/great victory/’ message.txt Highlight great victory	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.
Highlight the word victory in the output.	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.
Highlight the word success in the output.	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.
Highlight the word Success in the output. 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	As an assignment, try the below commands and see the output.
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Contributors and Content Editors

Nancyvarkey, Nirmala Venkat