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The first thing we need to do is obviously just create a new project.

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So I went ahead and did that.

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I named mine Clive for command line interface, but feel free to name yours whatever you want.

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So the next thing we're going to do is add in a couple of dependencies into our cargo Tamil file.

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And the first one is going to be called text color riser.

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We'll set the version to one and then rig X and we'll also set the version to one.

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So just to kind of show you what these dependencies are.

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Text Polarizer, it's just going to give us a couple of functions to enable and disable coloring.

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And this is just going to allow us to add some style to our output in the terminal.

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And then we have our Reg X crate, which is short for regular expression, and this creates going to

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allow us to look for a certain expression in our file and then we'll be able to.

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Change it based on some arguments that we're going to accept in.

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So this is a very important crate for what our program is going to do.

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So.

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Just to come back and look in here.

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We see we have reg x equals to one.

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Argo does is really cool thing where crate set of reached a 1.0 version in rust.

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They begin to follow semantic versioning.

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This means that all version one changes should maintain compatibility with older versions.

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So version 1.2 will be compatible with 1.3 and so on.

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But once version 2.0 is released, then 2.0 is.

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No longer required to be compatible with 1.0 versions.

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So another thing is, if you saw this in the Reg X.

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We're at version 1.5.4 is the latest, but in here we have it only as version one.

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So cargo also does this thing where if we specify, hey, we just want.

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One for the version is going to automatically use the newest available version prior to version two.

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So this one is essentially equivalent to version 1.5.4.

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So that's all we have to do in our cargo file.

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So now we can start looking inside of Main.

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And we can start thinking about our program structure.

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So our program is going to take four arguments a string to search for, a string to replace it with

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an input file and an output file so we can keep all of these arguments together by grouping them into

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and arguments struck.

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And all of our fields are going to be stringed.

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So we're going to have a pattern, which is what we're looking for.

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We're going to have replace, which is what we're going to substitute in for our pattern.

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And then we're going to have our input file and our output file.

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So to help us debug, we're actually going to add in an attribute called debug.

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So we're going to derive debug and this is just going to allow us to use.

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Standard output, a little better to kind of format how we want to be able to print out our argument

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struck to be able to see the values associated with our field.

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So it's just going to help us kind of debug our struc.

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And now we see that we have a bunch of warnings already for having dead code.

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So I actually want to suppress these that way when we output to the terminal, we don't get a ton of

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warnings outputted with it.

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I'd like to keep our output to the terminal pretty clean.

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And that's what allow dead code does.

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So now that we have our struct set up, let's just go ahead and bring in our text polarizer and we'll

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just bring in everything that's within the crate, which is what that wild card is going to do for us.

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It tells it to just make everything inside that crate available to us.

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So now we can create a new function and we'll call it print help.

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And in here, we're going to use a different form of print line.

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And it's going to be the print line macro.

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And the E print line is going to print to the standard air with the new line.

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So it is equivalent to print line, except the output goes to standard air instead of standard out.

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We should only use e print line for air and progress messages.

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Otherwise you should continue to use print line instead.

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So in here, let's just start adding in some messages to help the user understand how to use our program.

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So what is our program going to do?

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It's going to replace a string with a new string.

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And then our program, because we put in our curly brackets, it's going to be called find and replace.

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And then we want it to be green.

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So that's how we change the color in this case.

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And then we also want to print out how to use our program.

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So we'll say usage

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target string.

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Replacement string input file and then we'll have out put.

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File.

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And that's all we need to do.

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So let's come up here.

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Let's call our function.

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And now let's come down here and run it.

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And it's going to build our dependencies for us.

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Now we see that we have find and replace and our green text that we specified replace a string with

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the new string.

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And then we see that it has usage target string replacement string input file and output file.

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So everything looks good and everything was printed out the way it should be.

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So in the next lecture, let's look at how we can take in user arguments from the command line.