Linux - Regular expressions

now in this video I'm going to discuss

something about the regular expressions

now the name itself regular expressions

means the things which you use on the

regular basis commands which we use on a

regular basis all the text sequences

which you use on the regular braces

those particular commands or those

particular files became used by using

the regular expressions now now the

dragula expression is just a string

which can be used to describe several

characters we have so it can be anything

it can be your file content which you

want sequentially into a particular

output or you can you know modify the

contents without modifying the input and

you get the modified output that also we

can do by using this regular expressions

now if i'm talking about this regular

expressions they are used in a different

way by do using different commands so

dump some of the commands unlisted like

you use educ you use ah commands you use

grep commands so this commands which we

are going to see later how to configure

those particular commands or how to use

this particular commands so this

commands can be used to modify your

output without changing the input file

one of it we all generally use that is

yours it sews it is called as a stream

editor you already have yours STD in

file you have already have your SD out

well which we have already discussed

into these standard files so those

particular file we are going to use

while defining the output so what we are

going to do is we are going to put the

input or feed the input and / which

passes through or goes through your STD

outflow

without changing your STD info means if

suppose I have lists of numbers starting

from one to ten but I just want to check

the first five numbers or numbers which

are less than five so I can give a

command but just for looking the numbers

which I have less than five so the

command won't change the input file the

command won't change the original file

but only the output which I will get

that will be the one to Phi itself so

that is what the STD or STD is going to

use so let us see how we can use this

regular expression by

using your sed into your terminal so

such command as a set like you know we

can also use this particular search

command so that if I want to change the

output so for example I am going to

create the file name with fruits and I'm

going to add some fruits over here

Michael

I'm going to repeat it once more once or

twice as well

and again cherry right so I have added

some of the fruits now so now for

example I don't want apple and I want to

replace some other fruits in this

particular name that is this particular

file I do not want Apple and I want to

substitute something else

in spite of Apple what I can do is I can

use the substitution command so how you

generally use it so we will be using set

commands set and we need to define

substitute now what you need to

substitute and what for do you want to

replace I want to replace Apple with for

example grapes and in which file you

want to do it

fruit start sorry that is their fruits

file

okay just we need to define

so what I can do is I can just use

I'll sing the chords so that it subsets

and just a slash back slash and then

close the scores now it will accept the

same so you can see the Apple is

replaced by the gates but it won't

affect the original file again check

it's not a great you know affecting any

original file and you are getting you

know the worse you want to replace you

can replace same way I can you know

creative

company one and I'm going to add this is

production

company

the production is based on

software products right so this is the

you know the text I have written here

and I'm going to save the file and for

example now I want to just change the

production company to we can say a

deployment or a development company so

again I can substitute it in the same

way I can use a some onset yes / and

your what you need to change that is

production

with the word called us development /

and then the file name gender you can

see it has been changed the production

has been changed with the development

and the original file as it is

right so it won't affect that far same

way we can also do it as for the you

know globally and generate happens

globally all this particular file has

been changed all the name has been

changed now I can also use the

parameters that is G that it will do for

it globally means into this file the

number of words I have what the

development I can change it so this is

what exactly how we can change you know

particular particular letters or

particular words with different words so

this is what exactly we have seen into

this it come on we have many more

parameters of this it commands like see

this as very worst know the commands

generally we are generally used so you

can also use this set command like Mir

we can okay change the particular

instance of a lioness or like here we

can say we have seen we can change this

particular line globally right now

whatever if I want to if I do not want

to change it globally so what I will be

doing is

are they just changing the instance here

like suppose I have you know the

development returns over here and I want

to change not the oil but only on the

third line or only on the second line so

I can also refine to so it will change

the no.9 into this second instance what

generally we have so the same way like I

can take an example now

I'm just going to modify a file

and this is the company the same company

for a lambic to modify and I'm going to

add a line

if where I have repeated a same word

production as very

easy we can see okay so into one-liner

have at the production many times right

now I can find that

anyone production is over here and

production is over there same way if I

use the set command which I have used

earlier

not cheap but if I don't use this she

that is globally so what it will do it

will change the first instance not the

other instance which appeared in this

same line so if we want to change a

particular instance like if I want to

change particular instance that is

development into the second instance

only so we can check into the second

instance this production has been

changed but all the production's

generally we have into the first

instance has not been changed so this is

the way we can also you know use the set

command and whatever the changes I am

going to do here it is not going to make

any changes into any of my original file

that is company so for example if I want

this output of this you know changes and

I want to keep into the my order company

name like company one or company to I

can't define it so you can check for

both the files that is company one

company one and you can also check the

content of the company too

it will show you it has changed from

traction to development and this has

still production so I've just redirected

by one file entry into the waterfall

that's what we have seen and so this is

the set command saying they will have

many particular commands like your cut

commands we have on the dominie

generally you can use for modifying and

getting access to your particular part

of your data from your system so that is

what exactly we have so again we can use

a particular command called as a compare

command or we can say we can compare

both through two different files so you

can check out the difference between two

files like we have rigidbody files with

the name company right so company one

and company - now I want to check the

differences between this particular

files so I can give the command deff

company 1 & Company 2 now the lines

which are same as well show you the same

the lines which are different it will

show you the different lines so as this

is the company's file will you have this

had three lines we have added and they

start to compare two lines generally to

shrink you so we can also use if

commands to compare you know two

different file size over here

so some ethnicity as I told you there

are many things you normally we use in

today

you know Linux operating systems where

we do not affect your systems and in

daily usage in a regular expressions we

use it so you can find for it demand

pages and really you can find more of

the parameters of set and practice it so

into our next video I am going to

explore more about the file systems of

your Linux operating system and how you

create and manage your partitions so for

that keep watching and do practicing