Linux - Introduction Shell Substitution

now in this video we are going to talk

about the shell substitution now what is

substitution now we can run some of

these shell commands into our program or

into our any of the back console or we

can say into our prompt of your any

terminal and we can substitute any

particular command of shell into a echo

command so that we can get at the output

into it all we can substitute this

particular commands output to a

particular program as well so basically

we can say this cell substitution is

nothing but we are going to substitute

the shell commands into a particular

program so you can see the command

substitution means nothing more but to

run a shell commands and store its

output into a particular variable or

into an echo command so that we can get

the output the second we have the syntax

how we'll be using this particular

commands or how we'll be using the

substitution of your commands into this

shell so just we need to define the

command name or we can define the dollar

sign along with the command name so that

we can substitute into a particular

variable so this is what the command

substitution is now let's see how we can

use this command substitution into our

Linux terminal now a clean we helped you

know most of the commands which we can

substitute into this shell itself so let

us check this is stage I can even

substitute the date as son variable into

this year same way we can also use the

command Who am I or we can use who who

has logged in into different terminals

so this or any commands I mean whatever

they generally ish you know the terminal

commands we use we can add into the

shell as well so let us like how we can

substitute a command into a shell so

substitution is the name I am going to

define for this file and I'm going to

substitute a command know for example

I'll go and add mmm DT that is a

variable I'm going to add and I'm going

to add date into it

Eco date is our the variable DT let us

check

as such substitution so I can see now we

are able to City date correct so I can

also add more of the commands into it

current date is Gigi okay and always

remember that your Akane I'm not going

to use that single quote it's quite

amusing ts and great grave that symbol

so a son grave is again below your third

symbol so the next way the user it or we

can say the command which I can

substitute into this shell can be any

common like I want to check users who

has locked in okay so I can you've users

and then I can give it a come on again

into the same s and great symbol and I'm

gonna cook you who once you have done

with the who again I can give come on

list of login users on terminals right

so we can add this one we can also give

your time commands you know uptime

commands of your system so we can say we

I'm going to define the command called

as u P that is uptime or you can also

give UT any variable because uptime is a

by default to come on so I'm not going

to use up time so we can define the date

into it and along with the date we also

should know at what time we have locked

him so what I'll be doing is I'll define

date again I'll define thee

today's uptime done with that again HECO

so the login date and time was and I'm

going to define thee

YouTube's variable done with that save

it as such and I'm going to check for T

substitution not exist so you can see

current data this list of login users

okay so in the terminal I have not

defined the command into it sorry and

then the date and when we have logged an

so I just showing you the average time

the number of users Andy when we have

loaded with this so just I need to

modify it so that we can also get the

list of users so for that I haven't

defined the list of user into terminal

so I'll just raise my variable here so

for that I just define dollar

losers done with it again will run as

such substitutions and you can check it

is also showing you the number of users

has locked and into different terminal

and the log on date and time ran your

current date and time right so this is

what exactly we have seen how we can

substitute commands into a particular

variables even we can create a simple

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sample we can say a variable list or we

can say sample batch file kind of

okay and I can list the number of

commands if I do not want it to be added

into the commands so I can put a

sequence of no commands here like LS who

Who am I correct so I can save this and

once I run this father

can see all this particular commands

will get run automatically even though

if you have it we haven't added into the

variable so we can also use the commands

into these shells that bring files so

that whenever you run this particular

script all the commands should get run

so this is what we have talked about how

we can substitute a particular command

into the shells into later videos I am

going to explore more about your voting

mechanism so for that watch the next

video