WEBVTT

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Hello and welcome to Comment Line.

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This video we're going to go over

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piping in ampersand commands at the

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command line, how we can use them to

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our advantage to

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begin learning

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objectives. For this video, we're

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going to learn what piping and used

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for what the single and the double

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pipes do and understand

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what the single ampersand and the

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double ampersand operands are used

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for and how we can use them at the

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command line

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I preexistent, which often

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runs command to if command

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one fails, is it a

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command one single pipe command

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to be command one

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double pipe command to

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C command one single

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ampersand command two

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or D command one double

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ampersand command to

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answer is B command one

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double pipe command to.

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And as we'll learn in this

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video, the Double Pi will

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run a second command

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if the first command fails.

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This is very useful for trying to

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keep track of if a certain

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command is working properly

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or not.

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And similarly with the double

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ampersand, it will run command to

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its command. One is

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executed properly, not if

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it fails.

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So we'll learn more about this in

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this video.

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It's the single pipe.

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This is something that we've done a

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lot already. In this course, it'll

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take the standard output from the

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first command and it will pass it as

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standard input to this second

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in command.

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Very useful way to link two commands

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together. And it gives us a lot

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of really strong functionality

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and opportunity at the command line.

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And as we were using it, it's

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used a lot with less or more.

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And we can also use it with grip

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so that we can look through and grep

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for files and

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execute these different commands

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together by piping all of the output

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to the later commands.

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So very useful.

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You should be very comfortable with

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the signal because you're going to

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use it a lot at the command line.

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And it is a very, very effective

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way to utilize the output from

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commands in order to be able to

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run additional commands and

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manipulate that data.

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So the double pipe, this is used

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to execute a second command only

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if the first one fails.

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So this is really useful if you're

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looking for functionality or if

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we're using it in scripting where

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if we're running a script and we're

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going through a huge list of

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computer names and let's say

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that it cannot connect to a specific

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computer game.

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Well, if we use the double pipe, we

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can say, hey, if this command

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does not work for this computer

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because that computer's offline or

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it's not connected, shut down for

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whatever reason it is, then I want

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you to echo, hey, I

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can't connect.

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And as you can see in this first

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example, if we do ping,

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this house does not exist.

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It will echo, hey, I can't ping it.

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So let's give a quick

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demonstration of that.

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So we're going to do

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ping. This does not

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one not that

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exist.

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And this is not a real address.

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So there is no way is going to ping.

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It will do a double

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echo.

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I can't ping

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now since we know that this house

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does not exist, we can already know

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that this ping command is going

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to fail.

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Since we're using the double pipe,

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we know that it's going to execute

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this echo command.

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So check it out.

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So Ping request cannot not find the

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host. This does not exist.

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And since that command failed,

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it ran the echo command.

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I can't ping and

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now we can validate this where

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we can ping our lookback

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address.

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And this is one twenty seven 0.01.

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And if you're not familiar with the

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loop back, it is a non ratable

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only local system address.

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So we know that every single time

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is going to be able to ping this and

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since it can ping it, it's going to

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ignore this double pipe.

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So don't run through really quick

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and then we go and finish the ping

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and we did not get the echo.

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I can't ping because that

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first command executed properly.

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So we the ampersand, the single

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ampersand on windows, it

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is used to execute a additional

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command after the first command.

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This is not checked for any error

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or any success for the first

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command. And it is really

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useful be able to submit a bunch of

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different commands all on the same

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line. So this is a useful

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way to string a bunch of different

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commands all together, all at once.

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And if you're not familiar with

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Linux, it's similar to the

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semicolon on the Linux

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Shell.

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So we'll do a quick demonstration of

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that or I will do echo

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one, ampersand

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echo two.

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So it's going to do echo for one and

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then immediately execute Echo two.

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And as you can see, we have one end

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or two. So executed those commands

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directly.

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And it does not check for an error

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or success for

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Linux, the single ampersand

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is used to execute and run a

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process in the background.

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Now, when I'm using the Linux

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terminal, I like to use the single

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ampersand to start a

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new application from

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the command line and allows

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me to keep control of the terminal

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as well.

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So that's a really useful

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application of being able to use it.

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You can do a quick demonstration of

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that. So I have my Linux

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Mint machine up.

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Now let's say I want to

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open up Firefox,

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so I'm going to type in Firefox

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and a single ampersand

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and as you can see, is starting

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on page thirty six.

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Sixty two.

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I still have control over my

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terminal and Firefox

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is taking its time starting up.

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And here we go.

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So we've got Firefox up

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where if we just type Firefox

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without the let me spell

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it properly Firefox

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without the ampersand, then

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the terminal is going to hang and

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it will only give us access back to

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the terminal once

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Firefox is closed.

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So as you can see, we can type in

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everything, but nothing is not

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working.

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So let's close it out.

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And now it'll finally give us access

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back to the terminal.

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All right, with a double ampersand,

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so what this does is it will execute

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a second command only if the first

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command was successful, so

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it will only execute if there were

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no errors on this first command.

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So this is another useful way to be

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able to use these

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kind of operations in order to

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get what we need.

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So this is the opposite of the

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double pipe where if we ping

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our loop back address and say Echo

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good, we know every single time

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that is going to be a valid use.

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And then if we ping something that

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we know is not going to work, then

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we know that we are not going

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to get that echo

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because it only works on

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two on a successful

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command.

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So let's say ping

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two seven zero zero one

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double ampersand echo

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works.

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And since we know we can always ping

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our loop back address, it's always

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going to echo works

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that second command.

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Now, likewise, if we do

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a host that we know does not exist,

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this does not

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exist.

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And then we run the double ampersand

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and echo works.

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We know it will not work.

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We had the error for pain because

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it could not work properly and it

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did not execute that second command

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post assessment which operand will

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execute command to if command

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one is successful.

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Is it a command one

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single ampersand command to

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be command one double ampersand

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command to C

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command one single ampersands

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single command to

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command one double command

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to

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the answer is B command one

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double ampersand command to

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this operation will only execute

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command to if command one is

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successful and similar to the double

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play. This is a very useful

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way to be able to control the flow

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of data and help

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identify commands

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that should be running properly and

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should not.

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The single ampersand is used for

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its own specific ways and Windows

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and Linux not to help

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with the command flow.

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The single ampersand single pipe is

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not a valid combination of these

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characters, and the double pipe will

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only execute command to if it

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is unsuccessful for command one

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or two. In this video we learned

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what Peiping is used for, but single

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and double pipes do not understood

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the single ampersand in the double

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ampersand operands and

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how we can use them at the command

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line to our advantage.

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And I hope to see you in the next

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video.