WEBVTT

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Hello and welcome to Command Line.

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In this video, we're going to go

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over command redirection.

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I'm Christopher Haler.

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And let's begin this

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hour, learning objectives for this

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video. We're going to understand the

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purpose of redirection and why we

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should do it and how we can do it

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properly.

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Learn what this the greater

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than simple does, learn what

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the double greater than simple

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does and what the less

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than symbol does.

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So which operand appends

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to an existing file?

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Is it a single less

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than B A double less

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than C and double greater

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than or D a single

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greater than?

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The answer is C, the double greater

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than what this does is it will

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append to an existing file,

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whereas the single greater then will

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overwrite an existing file if it

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exists already.

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The single less than is

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used for input into

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a different command and the double

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less then is not a valid operand.

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So the redirection, the whole

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purpose of redirection from the

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command line is that we can use

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the output and either save

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it or we can direct input

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using the less than

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symbol so we can specify

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a different standard or standard

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error levels of redirection as

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well instead of just the normal

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output.

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So the useful way to be able to

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either gather information

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from the output of command that we

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can search through later or save

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it and keep it in a different place.

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So the single greater than what

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this does is it just simply takes

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the output from a command

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will stuff it into a file on the

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system.

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If the file does not exist,

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it will create it automatically.

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Now, the big thing to keep

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in mind single greater then is

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that it will overwrite a file if

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that file does exist.

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So that can be a problem

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if we want to keep the

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rest of the information that file

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already.

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So let's go ahead and give a

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quick demonstration.

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So I'm going to you there

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so we can see what's inside of this

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now, let's say Echo

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hello, and we're

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going to use the single ampersand

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and put it into

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hello to you

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or excuse me, not an ampersand, but

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single grader then and now.

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If we do another year, we could see

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we have hello to text

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and let's do type

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hello. And we could see hello

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there.

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And now if we do this again

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but instead of hello

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we have hi

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now with the single grader then it's

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going to overwrite that low

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and now we can do type again.

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We can see the Hillo is gone and all

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we have left is a high.

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Now in order to overcome

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this, we can use the double grid in

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it. And what this does appends

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to the end of the file if it does

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exist. So we don't want to overwrite

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everything in the file already.

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We use the double greater than and

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we'll automatically put it at the

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bottom of the file so we don't keep

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overwriting something that we want

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to keep in there already.

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And just like the single greater

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than it will create a file if it

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doesn't exist already.

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So let's give a quick demonstration

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of the double greater then and how

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we can use it to not overwrite what

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we're working on.

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All right. So let's say

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this didn't overwrite

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and the double grader then

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and load up to 60.

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Now, if we do type four.

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Hello, we can see we have this

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didn't overwrite on the

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end of the file

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that was already there and it did

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not overwrite the high that we

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previously just did.

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So this is very useful to keep in

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mind as we are

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redirecting output into files that

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we don't want to override, things

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that we want to keep in there.

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And we had the single graded.

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And what this does is it is used

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to provide input from a file

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into a command.

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And this file must exist

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because you are providing it has

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input and it will not

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change the input of the file.

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So it will leave the file.

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The same will simply provide that

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file as input into

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the command so we can

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use the sort command and

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the less than to say, hey, I'm

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pushing this file that text

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into the sort command,

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so let's give a demonstration and

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then I'm going to pull up my Linux

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machine.

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And just like always, I'm going to

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type LS to see what is inside

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of this directory.

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And now let's say I want to sort of

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Latin words that you

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sort

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and Latin words that txt

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with my less than simple

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and look that goes ahead takes it as

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input sorts Morlot from

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pretty useful.

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And now we can also redirect

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standard error from

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commands as well, and this is

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something you may have seen already

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where if there's a lot of error

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text, especially if you're doing a

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search and

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the command doesn't have full access

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to the system, it will give you

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error saying, hey, I can't reach

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this. And that can take up a lot of

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screen information.

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So we can do is we can redirect

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that standard error into a place

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that doesn't exist on Linux.

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That is Dev no

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dev signal and anything sent

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to this directory on

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Linux is immediately dropped and

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just ignored.

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And now in order to specify a

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standard error, we're going

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to use the two and then the

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single greater then.

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And this says, hey,

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for any errors that you get while on

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this command is running, I want you

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to take it and spit the

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standard error into this

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specific location and using

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the div. No, it says

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just get rid of it.

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So this is a useful way to be

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able to ignore all of the

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error information.

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So let's say I'm going to use my

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Linux machine and I'm going to

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search for my program

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on the root of the drive.

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Now, as you'll see,

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let's take the report

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I my program

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forward, slash the route.

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Now you'll see I will have

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a lot of

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this, my bad history,

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and now I should have a lot of

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permission denied, not go.

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So there's way too much going on

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right here.

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It's taken over my entire terminal.

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I, I'm going to use controls

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to stop this before it takes

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up more space and then

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do clear Nancy

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less so that I can get back to that

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kind of default position

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on the terminal.

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Now, if I do

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too, Divx

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know the saying,

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I want you to take these standard

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error and push it into Dev.

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No.

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So as we'll see, we won't get all

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those errors because it's

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all the error messages that

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it gets automatically sends to

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that.

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There's no directory

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where it is dropped by the limbic

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system.

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So that way we can focus on directly

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just what the output

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we have.

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So here we go. So we can already see

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some different

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information coming back.

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And we don't have all these error

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messages coming all over the screen

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and taking over our

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our our command

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window. Excuse me,

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I supposed to system, which often

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overrides an existing file.

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Is it a single less than

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the less than

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C a single greater

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then or D a double greater than

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the answer is C a single greater

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than this will overwrite an existing

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file and it will not

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append to the end of the double

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greater than will append to the end

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of a file if you want to keep it.

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But if you don't care too much about

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it, or you just need to create

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a new file, the single greatest

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work, exactly what you needed to do,

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and the single less than

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is used to provide input

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to a command not to

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get the output for it.

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All right. So in this video, we

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learned the purpose of redirection

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and how we can use at the command

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line, learned what the single

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greater then does learn with the

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double greater than does and how it

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happens to the file and keeps the

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file and understood with the single

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less than does and how we can use

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it to our advantage.

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And I hope to see in the next video.