Difference between revisions of "Linux/C3/More-on-grep-command/English"

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(Created page with ''''Title of script''': The grep command and Regular Expressions '''Author : Anirban Roy Choudhury''' '''Keywords:Search,Pattern,regular expressions,extended regular expression'…')
 
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'''Title of script''': The grep command and Regular Expressions
 
'''Title of script''': The grep command and Regular Expressions
  
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'''Author : Anirban Roy Choudhury'''
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'''Author : Sachin Patil'''
  
 
'''Keywords:Search,Pattern,regular expressions,extended regular expression'''
 
'''Keywords:Search,Pattern,regular expressions,extended regular expression'''
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Display the previous slide only and narrate this line.
 
Display the previous slide only and narrate this line.
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| style="border:1pt solid #000000;padding:0.106cm;"| The script has been contributed by Sachin Patil.
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This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.
  
 
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Revision as of 15:35, 1 July 2013

Title of script: The grep command and Regular Expressions

Author : Sachin Patil

Keywords:Search,Pattern,regular expressions,extended regular expression


Visual Cue Narration
Display Slide 1


Welcome to this spoken tutorial on some more on grep command
Display Slide 2 In this tutorial we will learn some more grep commands.
Display Slide 3 To record this tutorial, I am using

Ubuntu Linux 12.04 Operating System and

GNU BASH version 4.2.24(1)

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

Display Slide 4 To practice this tutorial,

You should know Basics of linux terminal.

You should be aware of grep.

For relevant tutorials please visit our website:

http://spoken-tutorial.org

At the prompt type

“grep -e “electronics” -e “civil” grepdemo.txt” [enter]

We can match more than one patterns as well.

Then we have to use the -e option.


Say we want to find information for those who are either in civil or electronics.


We need to type:

grep space minus e space in double quotes electronics space minus e space in double quotes civil space grepdemo.txt

Press Enter.

At the prompt type

“grep -ie “choudhury” -ie “chowdhari” grepdemo.txt” [enter]

Say you need to look into people whose title is choudhury.


The problem is different people spell their titles in different way.

So what is the solution?.


In such cases we can use minus e option with minus i.


Type:


grep space minus ie space in double quotes choudhury space minus ie space in double quotes chowdhari space grepdemo.txt

Press Enter.


But there can be many other ways in which we can write the name.


How many -e options can we give.


Obviously there needs to be a better way and that way is through Regular expressions.

Display Slide 5 A regular expression provides a concise and flexible means for matching strings of text.


Such as particular characters, words or patterns of characters.

There are a number of regular expression characters.

Let us see them one by one.

Display Slide 6 The character class.

It allows us to specify a group of characters within a pair of square brackets .


Only one out of this group of characters is matched.

Eg. [abc] would mean that this regular expression matches either a or b or c.

At the prompt

grep -i “ch[ao][uw]dh[ua]r[yi]”

grepdemo.txt [enter]

Like to match choudhury we may use the command

type at the prompt


grep space minus i space in double quotes ch[ao][uw]dh[ua]r[yi] space grepdemo.txt


Press Enter.

It still does not match choudhuree

Display Slide 7 If we want to specify a large range then write:

first letter dash last letter of the range


Like to match any digit we simply write [0-9].

Display Slide 8


The * refers to 0 or more occurrences of the immediately preceding character.


For example ab* can match a,ab,abb,abbb etc.



At the prompt

grep -i “m[ei]*raa*” grepdemo.txt


[enter]


So to match the students name whose name is Mira

We write at the prompt:


grep space minus i space in double quotes m[ei] asterisk r a a asterisk space grepdemo.txt


Press Enter.

Display Slide 9 The dot “.”

This regular expression matches any one character.

At the prompt

grep “M...” grepdemo.txt


[enter]

Say we want to search any words that are 4 letters long and start with M.


We would simply write


grep space in double quotes M... space space grepdemo.txt

Press Enter.


Here the space within the quotes is important.


As it would match 5 or more letter words.



Display Slide 10 We may be specific about where in the line we want to search for our pattern.


It may be at the beginning of the line.


For that we have the caret sign.

At the prompt


grep “^A” grepdemo.txt


[enter]

Now if we want those entries whose roll numbers start with A.

We know that roll is the first field in the file.

We write at the prompt:


grep in double quotes caret A then space grepdemo.txt


Press Enter.

Display Slide 11


At the prompt, type:

grep “[78]...$ ” grepdemo.txt


[enter]

Similarly to match a pattern at the end of the file, we have the dollar sign.


To find stipends between 7000 to 8999 we have to write:

grep space in double quotes [78]...dolar sign space grepdemo.txt

Press Enter


This brings me to the end of this tutorial.

Display Slide 12

Summary

In this tutorial we learnt,


To match more than one pattern

eg. grep -e “electronics” -e “civil” grepdemo.txt


To check a word that has different spelling

eg. grep -ie “choudhury” -ie “chowdhari” grepdemo.txt


Character class

eg. grep -i “ch[ao][uw]dh[ua]r[yi]”

grepdemo.txt


The use of *

eg. grep -i “m[ei]*raa*” grepdemo.txt


To match any one character using dot

eg. grep “M...” grepdemo.txt


To match a pattern at the beginning of the file

eg. grep “^A” grepdemo.txt


To match a pattern at the end of the file

eg. grep “[78]...$ ” grepdemo.txt



Display Slide 13 As an assignment,

List those entries that are 5 letters long and starts with Y.

Display Slide 14

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

Display Slide 15

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

Display Slide 16

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 signning off. Thank you for joining.

Contributors and Content Editors

Ashwini

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