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Welcome to the spoken tutorial on More on sed.

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In this tutorial, we will learn some more on sed commands through some examples.

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To record this tutorial, I am using

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*Ubuntu Linux version 12.04 Operating System and

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*GNU BASH version 4.2.24

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Please note, GNU Bash version 4 or above is recommended to practice this tutorial.

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As prerequisites,

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You should know basics of Linux terminal.

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You should be aware of sed tool.

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For relevant tutorials, please visit our website which as shown: http://spoken-tutorial.org

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The major use of sed is substitution.

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Replacing some pattern in the input with something else.

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Let's first look at the original file seddemo.txt.

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Notice that the word "Kumar" occurs two times in the fourth line and once in the sixth line.

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If you want to replace all occurrences of "Kumar" with "Roy",

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type on the terminal:

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sed space within single quote s front slash / opening square bracket small k capital K   closing square bracket umar  slash Roy slash after the single quotes space seddemo.txt

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Press Enter.

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Notice the fourth line.

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Only the first occurrence of "Kumar" is changed to "Roy", not the second one.

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Sixth line had one occurrence of the word "Kumar" and this is replaced now.

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So, we see only the first entry of the lines has been changed.

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This is because, by default, the first matched entry of any line is substituted.

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To substitute all the matched entries we need to use the flag  g option.

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Let me clear the prompt.

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Type:
sed space (within single quotes) 's front-slash opening square bracket small k capital K closing square bracket umar slash Roy slash g'  after the single quote space seddemo.txt. Press Enter.

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Now, both entries of the fourth line are replaced.

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We can make multiple substitutions in one go as well.

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Say, we want to replace the word "electronics" with the word "electrical"

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and "civil" with "metallurgy" in the file seddemo.txt.

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Let me clear the prompt

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Type:
sed space hyphen e space within single quotes ‘s front slash electronics slash electrical slash g’ after the single quote space hyphen e space within single quotes  ‘s front-slash civil slash metallurgy slash g’  after the single quotes space seddemo.txt

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Press Enter.

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You can see that the words are replaced.

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Now we want to change the stream of 'Anirban' from "computers" to "mathematics."

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In such case we would need to type:

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sed space within single quotes  'front-slash Anirban slash s slash computers slash mathematics slash g'  after the single quotes space seddemo.txt

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Press Enter.

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We see that the stream is changed.

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Let us understand what this is.

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First we write sed, then in single quotes we write the pattern to be matched.

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This is "Anirban".

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Now after the slash comes the operation.

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This is 's' that stands for substitution as we have already seen.

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Then we mention the pattern to be replaced which is "computers".

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Then the new word that would be substituted which is "mathematics".

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We can also use sed to add or delete lines in the file.

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Say, we want to select those lines which do not have stream as "electronics."

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For that, we have the d flag.

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Type:
sed space within single quotes front-slash electronics slash d after the single quotes space seddemo.txt space greater than sign space nonelectronics.txt

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Press Enter.

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To see the contents, type: cat space nonelectronics.txt.

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Say, at the start of the file we want to add a line Student Information.

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For that we have the i action.

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We need to type: sed space in single quotes '1i space Student Information' after the quote space seddemo.txt

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And press Enter.

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You can see the output.

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In fact, we can enter multiple lines like this.

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Say, we want to add the two lines. We would do it in a similar way.

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Along with Student Information we also want to add academics in the next year.

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So in that case we would write
sed space in single quotes 1i space Student Information slash n 2013 after the quotes seddemo.txt

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Press Enter.

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Notice slash n between the string ‘Information’ and ‘2013’.

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slash n prints 2013 in the next line after ‘Student Information’.

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This brings us to the end of this tutorial.

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Let us summarize,

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In this tutorial we learnt:

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* Substitution

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* Replacement

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* And Insertion.

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As an assignment, use the same text file seddemo.txt

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and try to replace or substitute name "Ankit" with "Ashish".

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Watch the video available at the link shown below http://spoken-tutorial.org/What_is_a_Spoken Tutorial

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It summarizes the Spoken Tutorial project.

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If you do not have good bandwidth, you can download and watch it.

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The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials.

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Gives certificates to those who pass an online test.

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For more details, please write to contact@spoken-tutorial.org

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

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It is supported by the National Mission on Education through ICT, MHRD, Government of India.

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More information on this Mission is available at the link shown below: http://spoken-tutorial.org\NMEICT-Intro.

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The script has been contributed by Anirban and Sachin.

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This is Ashwini PAtil from IIT Bombay, signing off.
Thank you for joining.