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The beautiful people.

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Now, in the last few lectures you've been doing so much stuff with files you've been, you've learned

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how to create them, move them around, copy them, delete them, paste them, rename them and search

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for them, and so much more, all from the command line.

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But even though we can now manipulate files on a grand level, we haven't really seen how to take a

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quick peek at what's inside them and manipulate their contents yet.

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Well, that's what these next few videos are for.

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Over the next few videos, you're going to be learning five new commands that will allow you to manipulate

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file contents.

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So this is stuff such as reading files, reversing files, and even sticking files together, as well

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as reading them in some paging programs.

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So what this is going to allow you to do is to get most of your work done from the command line without

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ever having to need to open up external editors, which is going to be a massive productivity boost,

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and it's going to help you keep you inside the whole command line work process ecosystem.

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So this is going to be very, very useful.

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It's kind of like a missing piece at the minute.

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And after it all, after the end of the next few videos, you're going to be out to perform a whole

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bunch of useful functions on the contents of files, which, when combined with what you know about

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manipulating files in their entirety, is going to make you the file manipulation master.

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So let's just go ahead and jump right into it.

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Okay.

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So the first command that we're going to take a look at is the cat command.

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Now, do you remember those kitten jokes that I was talking to you about earlier?

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Well, meow.

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So now you've actually seen the cat command before.

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So this will be a rather nice refresher.

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Okay.

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So you can see here on our desktop, we've got a few files.

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We've got far one file two, file three, file four and file five dot txt.

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So let's take a look at what's inside the first file.

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But instead of opening it, we're going to look in our terminal to see what's inside the file.

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Okay.

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So if we type cat and then file.

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Oh, I need to be on the desktop, don't I?

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So let me change the desktop.

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I click the screen and then type cat and file one dot txt.

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I'm going to press enter.

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We'll see that the contents of the file have been written to standard output and we can see that the

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file contains the word hello.

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Now if I press if I double click that and open that graphically, we can see that.

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Yes.

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All that file contains is the word hello.

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Okay.

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So using the cat command, we managed to get that the contents of the file printed to standard output.

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Okay.

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So let's try and see what's in file number two.

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Okay.

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So if we do that file to txt, we can see the word there is inside.

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Hmm.

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I guess I guess you can imagine where this is going.

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Right.

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So if I go file three, it says you file.

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I see file four.

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It says beautiful.

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And I bet we can all guess what's in file number five.

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So if I press five, it says people.

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Okay, so if you put all the five files together, it says hello there, you beautiful people.

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Well, what a coincidence.

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I wonder how that happened.

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So, in fact, you can actually use the cat command to stick files together.

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And that's actually usually what it's for.

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Cat is short for the word concatenate, which is a fancy word for stick together.

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So what cat does is stick together all of the input files and then pass that that stick together stuff

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to standard output.

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Okay.

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So if we do, if I click the screen, if we do cat file one txt file to txt file three point text file

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for txt and file five dot txt and press enter.

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You can see that.

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Hello there you beautiful people has been made by sticking together the five different files and then

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that has been printed to our standard output.

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But we can of course redirect this to a new file called Beautiful txt on our desktop, which we see

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has been created here.

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And when we open that, we now see that we've got a new file that says Hello, are you beautiful people

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that has been created by sticking together five other files.

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Now we can actually you can see this command line here is quite long, right?

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Well, we can actually simplify that using our knowledge of wild cards.

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So instead of having cat file 1.2, see file 2.2 key file three point text file 4.2 and 55. txt.

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You can just use a wild card like this cat together files 1 to 5 dot txt into beautiful.

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So if I if I delete beautiful that text and run that wild card and it's been created again and we can

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see here that yep we get exactly the same result.

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Hello there, you beautiful people, but a lot less typing.

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So that's pretty cool.

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Right now the cat command, when you want to stick files together like this, it's useful for sticking

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together text files, obviously, but it can be very useful when working with audio or MP3 files, for

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example.

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So you could have multiple different single MP3 files, you know, different songs, for example, but

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you can actually concatenate them together, stick these different files together to create one long

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file that has all the music in it.

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So that's pretty epic.

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So the cat command is used to stick files together, or actually if you want, just read the contents

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of a file so we could just do.

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Cat beautiful txt so.

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Cat beautiful txt and we can see the contents of any of any file which is really, really useful.

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But another command that I want to take a look at is the tac command.

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So let me just clear the screen here.

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So the tac command is just cat spelled backwards and it's used to reverse whatever it receives as an

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input.

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So if we make a file called Alpha txt by echoing let's say ABC to Alpha txt and we're going to also

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echo d e f to alpha and notice the way that we've got two arrows here because we're going to append

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to the same file rather than overwrite it.

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Okay.

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So now if I look in alpha txt we've got ABC on one line and def on another.

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So if we read the file, we read the file using cat we sue cat alpha txt we get abc then d e f okay,

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but let's see what happens if we read it using tac.

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So instead of cat, we read it using tac, which is the cat spelled backwards.

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And you see now that we get def then ABC.

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So you can see that the tac command actually reads the whole file in reverse but leaves the file the

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lines the same.

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So it just wrote the last line first and then the first line last.

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Right?

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But it didn't affect any text on each line.

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So if we stick together the various different files here, the file 1 to 5 using cat.

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So if we do file 1 to 5 dot txt, you see that we get the output there.

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But now I want you to think what might happen if we pipe that into TAC?

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Now TAC will reverse the file line wise.

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So the last line will be printed first and the first line will be printed last.

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So what do you think might come out of this?

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Just take a couple of seconds.

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Ever think about it?

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So what might happen is the last line, which is people would come first and the first line would come

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last.

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So what might come out is people beautiful?

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You there?

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Hello?

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Okay, so let's have a look.

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There we go.

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Yeah, people beautiful.

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You there?

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Hello.

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So think of the tag command as reversing a file vertically.

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Okay, so it just flips it upside down.

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It doesn't affect any of the lines, it just flips it upside down.

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And of course, because this is all being printed, the standard output, you can of course redirect

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it into another file called reversed tcd and here we are.

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Here is reverse text.

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When we open that, we see that we've saved the output in that file.

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So that one good thing about the tac command where it can be used is again, if we take the example

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of MP three files, I don't know if you've ever seen those videos online where people say, Oh, look

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what this song says when it's played backwards.

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And like, you know, they tried to say it's got some hidden messages in the file.

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Maybe you've seen those kind of videos.

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Well, maybe they were made using the tag command because if you run an MP three file through through

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the command commands, if I did something like tack my file the MP three and save that into another

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my reversed file dot MP three then this file, this one here will be the same song but played backwards.

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So that's something to to potentially give a go if, if, if you would like.

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Okay, so that's the tac command.

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The tac command will reverse files vertically.

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There's one other that I want to look at, which is called the Rev Command.

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So the Rev Command allows you to reverse the content on each line.

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So if I clear the screen and we cut together the various different files, again we get hello there,

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you beautiful people.

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But if I pipe that into the rev command, look what happens here.

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It's still saying if you can read it, it still says hello there, you beautiful people.

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So the lines are vertically the same, but horizontally they've been reversed.

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So the last letter of each line.

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So here's the o has is now become the first letter and you know it's reversed them along the lines but

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the order of each line is the same, if that makes sense.

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If we if we put the the tac command, you can see that people is the first line, whereas here people

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is the last line.

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But the letters have been reversed.

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So this is the way you can think of rev and tack.

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Tack reverses a file vertically and rev reverses a file horizontally.

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Okay.

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Now you can really jumble up files by piping it through both of them.

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So if I pipe it through tack, it's going to reverse vertically.

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But then if I pipe that also through rev, you've now got a vertically reversed and horizontally reversed

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file, which is a good way of jumbling up stuff if you ever find that particularly useful.

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But yeah, just to make it easier, just think of tack as reversing files vertically in columns and

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you can think of Rev as reversing files horizontally across the rows.

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So all of these commands, whether it be cat or it be tack or it be rev, all they're doing is they

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are taking a file and reading it into standard input, doing some processing and then, you know, just

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spitting that the output to standard output.

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Okay.

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So they're a good way.

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Well, cat is a good way of reading files and you know, the others are a good way of jumbling up stuff.

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But the problem is when you read files to the terminal like this, if a file is particularly long,

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it can really just clog up your screen and it's not very useful and you find yourself scrolling a long,

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long way.

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So if we try to find a file that's quite large, so if we say, for example, let's use the find command,

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let's search our system up to, let's say a maximum depth of four.

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We don't need to go too far for any configuration file.

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So a name that ends in com and a size that let's say over 20 kilobytes so we are we only get we only

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get two really.

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But there's one here in called cups browser.

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And this is to do with like printing services and it's apparently a, it's a rather large file.

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So if I copy it, copy that and try to cut it out.

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Okay.

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So if I try to cap that, oops, you see, you see it just happen right there.

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If I tried to cap that out and press enter, you see that we've just shut down a stupid amount of lines.

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Can you see?

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Now, if I wanted to have a look at it, I ended up scrolling all the way through here.

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It's not very good, right?

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So that's a problem when you're dealing with stuff on the command line.

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And we want a more elegant solution to dealing with relatively large files.

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And sometimes, you know, if I if I just wanted to read out of how maybe I don't want all of the file,

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maybe I only want a certain snippet of it.

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Maybe I only want the top ten lines or the bottom ten lines or something like that.

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And we need to have a better way of being able to deal with file contents on the command line.

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So in summary, so that's what we're going to be covering in the next video.

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But in summary of this video.

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We've seen that the cat command can be used to actually read out files.

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So if I look at Beautiful on our desktop, if I read out beautiful text, we can read that out.

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If we want to reverse files vertically, we can use tack.

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If we want to reverse files horizontally, we can use rev.

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But all either way, all of these.

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What they're doing is they are just reading a file's content and spitting it out to standard output

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where you can then of course pipe it into other commands to do other processing or like while you're

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working on the command line, if you just want to see quickly what's in a file, you can just you can

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just use cat the cat command and then see that really quickly and get on with what you were doing.

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Okay.

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So there we are those those are the cat tack and rev commands.

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But in the next video, we're going to take a look at how you can level up this ability to do more sophisticated

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things.

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So I'll break the video here and see you in the next video.