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

Through some examples

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.

You should know Basics of linux terminal.

You should be aware of grep.

For relevant tutorials please visit our website:

http://spoken-tutorial.org

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

Then we have to use the -e option.

I will use the same example grepdemo.txt

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

We need to type:

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

Press Enter.

The output is displayed.

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

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

So what is the solution?.

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

Type:

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

Press Enter.

The output is displayed.

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.

Such as particular characters, words or patterns of characters.

Let us see them one by one.

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.

grep -i “ch[ao][uw]dh[ua]r[yi]”

grepdemo.txt [enter]

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

Press Enter.

The output is displayed.

It still does not match choudhuree with double e.

first letter dash last letter of the range

Suppose we like to match any digit we simply write [0-9]. One out of this group of characters is matched.

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

grep -i “m[ei]*raa*” grepdemo.txt

[enter]

We write at the prompt:

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

Press Enter.

The output is displayed.

This regular expression matches any one character.

grep “M...” grepdemo.txt

[enter]

We would simply write

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

Press Enter.

The output is displayed.

Here the space within the quotes is important.

As it would match 5 or more letter words.

It may be at the beginning of the line.

For that we have the caret sign.

grep “^A” grepdemo.txt

[enter]

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.

At the prompt, type:

grep “[78]...$ ” grepdemo.txt

[enter]

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

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

Press Enter

The output is displayed.

This brings me to the end of this tutorial.

Let us summarize.

Summary

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

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

Acknowledgement Slide

It summarises the Spoken Tutorial project

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

Spoken Tutorial Workshops

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, please write to

contact@spoken-tutorial.org

Acknowledgement

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

Display the previous slide only and narrate this line.

This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.