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This is a really exciting lecture
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cause you're gonna learn how to read data from files,
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and also how to write data into files.
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And we already imported the built-in module
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that we need for that in the last lecture,
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and so let's now get rid of this code
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and start using the FS module.
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So we use fs.readfilesync, okay.
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And sync stands for synchronous,
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and you will start learning about synchronous
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and asynchronous right in the next video, okay.
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So this is the synchronous version of file reading.
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There is also an asynchronous version.
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So, the read file sync function takes two arguments.
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The first one is the path to the file that we're reading
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and then also the character encoded.
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So, first the path to the file,
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and the file is in the txt folder,
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and it is the input one.
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So, this text that I have here about the avocado
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is what we're gonna read into a variable.
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And I'm not sure if you're gonna be able
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to see this emoji here right on your operating system,
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but if you're on Windows 8 or Windows 10
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then that's probably going to work just fine.
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Okay, so we specified a path there,
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and there are multiple ways of doing that,
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but for now I'm gonna go with the simplest one.
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So, all I'm gonna do is set it in the /txt/input.txt.
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So again, we're starting at the home folder,
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which is basically the folder
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where the index.js file is located,
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so that's the dot in there,
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and then we move into the txt folder,
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and from there input.txt.
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Then here the second one we have
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to define the character encoding,
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which is utf8, usually,
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at least if you're just using English.
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Okay, and if you don't specify this,
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we get back something called a buffer, okay,
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and that's not really what we want.
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We really just want the text.
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And so, calling this function here will now read the data
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from the file and return it to us,
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and so we need save that somewhere
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and we put it into a variable.
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So let's say textIn because it's a more text input.
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Okay, and then let's log it to the console
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just to see if it works.
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Give it a second, and now we need to run this here again.
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So in the terminal, I can just use the up arrow
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to run the previous command.
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So here it is nodeindex.js again.
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Hit return, and let's see, and indeed here we go.
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So here is the content of that file.
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So, perfect.
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We now know how to read stuff from files.
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Congratulations.
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Okay, but we also want to know how to write to files.
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So let's create some new variable here with some more text,
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and then write it into a new file.
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So let's call that one textOut, so for output.
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And basically let's just write a string
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where we will then include this text in.
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I'm gonna be using a template string here,
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and at this point I'm gonna assume
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that you're kinda familiar with the es6 syntax, okay.
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So we already used const here,
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which is an es6 way of declaring variables instead of var,
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and now the template string, which is another es6 thing.
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So before the es6, if you wanted to add something
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to text in, you would have to use the plus operator.
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So let's say, "this is" and then space and then text in.
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Okay, so you would have to use the plus operator,
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but if it's a template string it's much easier.
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All we have to do is use the backticks, then some text,
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and then into this string you can
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very easily plug in the variable.
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So let's say, "This is what we know about the avocado."
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Then we use this syntax to input the variable, okay,
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and so basically inside of these curly braces here
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we can write any JavaScript that we want.
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So it's not just for plugging in variables straight away,
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we can also do a lot of calculations
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or any javaScript expression that we wanted in here.
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Now, let's say a new line character.
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So that's a new line, okay.
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And just to show you that we can actually use JavaScript
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inside of these curly braces here.
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So this dollar sign and then curly braces.
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So date, or actually date like this, dot now.
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Okay, so that is our string,
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which has this text here in together with the text
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that we read before from the variable.
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And so now let's write that to a new file.
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So again, we use the FS module,
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and this time, writeFileSync.
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Okay, and again we specify the path to the file,
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and we still want it in the txt folder,
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and we call it output.txt, okay.
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And now we have to actually specify
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what we want to write into that file, right,
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and tell us the text out variable.
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And this doesn't return anything meaningful
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until we don't save anything to any variable.
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All we do is to finally log something more to the console,
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like just informing if the file has been written.
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Okay, so let's test it out again.
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I'm gonna clear the console with command K.
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Hit the arrow up key, enter, and maybe you saw it.
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We here now have this new file called Output,
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and if I open it up, then you see,
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"This is what we know about the avocado,"
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which is what we wrote in the index.js,
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and then this is the text that came
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before from the input file, right.
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Then the new line that we created,
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and then created on this date basically.
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So this is date.now,
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so it's just a timestamp in milliseconds.
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All right, and this is how you read
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and write to and from files in Node.JS.
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