Linux/C3/More-on-sed-command/English

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Title of script: More on sed

Author: Sachin Patil and Anirban

Keywords: sed, substitute, insert, delete


Visual Cue Narration
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Welcome to the spoken tutorial on More on sed.
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Learning objectives

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


To record this tutorial, I am using
  • Ubuntu Linux 12.04 Operating System and
  • GNU BASH version 4.2.24

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

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Prerequisites


As prerequisites,

You should know basics of Linux terminal.

You should be aware of sed tool.

For relevant tutorials please visit our website:

http://spoken-tutorial.org

The major use of sed is substitution.

Replacing some pattern in the input with something else.

Type

cat seddemo.txt


[enter]


[ Point to the fourth and sixth line ]

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


Type


sed 's/[kK]umar/Roy/' seddemo.txt


[enter]

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


If you want to replace all occurrences of ‘Kumar’ with ‘Roy’, type on the terminal

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

Press Enter.

Show the output


[point to 4th line of both output and file]

Notice the fourth line.

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

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

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

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

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


sed 's /[ kK]umar/Roy/g' seddemo.txt


[enter]

Let me clear the prompt. Type

sed space within single quotes 's /[ kK]umar/Roy/g' after the single quote space seddemo.txt

And press Enter

Now, both entries of the fourth line are replaced.

We can make multiple substitutions in one go as well.

Say we want to replace the words electronics with the word electrical

And civil with metallurgy in the file seddemo.txt

Type


sed -e 's/electronics/electrical/g’

-e ‘s/civil/metallurgy/g' after the single quote space seddemo.txt


[enter]


Type:

sed space -e space within single quotes ‘s/electronics/electrical/g’ -e ‘s/civil/metallurgy/g’ after the single quote space seddemo.txt

And press Enter.

You can see that the words are replaced.

Type


sed '/Anirban/s/computers/mathematics/' seddemo.txt


[enter]

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


In such case we would need to type:

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

Press Enter.

We see that the stream is changed.


[highlight text inside single quotes]


[highlight ‘Anirban’]


[highlight ‘s’]


[highlight ‘computers’]


[highlight ‘mathematics’]

Let us understand what this is.

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


This is Anirban.

Now after the slash comes the operation.

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

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

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

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

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

Type


sed '/electronics/d' seddemo.txt > nonelectronics.txt


[enter]


For that, we have the d flag.


type:

sed space (within single quotes) (front slash) /electronics/d after the single quotes space seddemo.txt space greater than sign space nonelectronics.txt

Press Enter.


cat nonelectronics.txt


[enter]

To see the contents, type:

cat space nonelectronics.txt

and press Enter.

Type


sed '1i Student Information' seddemo.txt


[enter]

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

For that we have the i action.

We need to type:

sed space in single quotes '1i space Student Information' seddemo.txt

And press Enter.

You can see the output.

In fact, we can enter multiple lines like this.

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

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


Type


sed '1i Student Information\n2011' seddemo.txt


[enter]

So in that case we would write


sed space within single quotes i space Student Information \n 2013' after the quotes space seddemo.txt

Press Enter

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

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

This brings me to the end of this tutorial.
Summary Let us summarize,

In this tutorial we learnt,

Substitution

Replacement

Insertion

Assignment As an assignment,

Take the same text file seddemo.txt

And try to replace or substitute name Ankit with Ashish

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Acknowledgement Slide


Watch the video available at the link shown below

It summarises the Spoken Tutorial project

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

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Spoken Tutorial Workshops


The Spoken Tutorial Project Team

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, please write to

contact@spoken-tutorial.org

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Acknowledgement


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

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

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

No Last Slide for tutorials created at IITB

Display the previous slide only and narrate this line.

The script has been contributed by Sachin Patil.

This is Ashwini PAtil from IIT bombay sighning off.

Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey