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Now that we have an understanding of engine X variables we can move on to rewrites or simply redirect.

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In some cases the two directives we can use for rewriting requests is the rewrite directive and the

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return directive which we've already used several times throughout this course and being the same bluff.

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The two very importantly however the return statement as we've been using it takes a status code and

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response data or strings.

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But in the case of that response code being a 300 variant which is four redirects the return directives

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behaviour changes in it then except a you are dry as the second parameter.

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A You are right.

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To which the client should be redirected.

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For example at the moment we can access the demo sites image by requesting thumb dot P in G.

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But let's say we also want to serve this image for Slash logo which obviously right now returns a foro

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for we can create a simple redirect using the return directive.

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I'll get rid of all these bits from the previous lesson.

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Change this location to that slash logo.

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You are right.

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And in this location return a 3 0 7 so a temporary redirect again or 300 status codes being redirects

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of some sort.

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And what we want to return is slash thumb.

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Dot P in G.

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We could also have made this a complete.

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You are right with protocol host etc..

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But a relative you are I will be fine as this is redirecting to the same host as the request this coming

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from save this reload the configuration and now when we reload this request for Slash logo we get the

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thumb doppie G image.

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But very importantly note that the u r l changed to thumb don't be in G.

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Which is essentially the main difference between rewrites and redirects a redirect simply tells the

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client performing the request.

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Where to go instead a rewrite.

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On the other hand mutates the you are right internally.

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So let's see an example this time in the server context before matching the request to any location

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contexts.

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We can say rewrite.

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Pass a regular expression with which to match the you are I.

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I'll say Carrott So starting with Slash user slash and then W. plus.

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So more than one word character with the second argument being the new you are try to rewrite this to

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slash greet.

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Now here's the important thing to understand about rewrites.

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When you are IE is rewritten it also gets re-evaluated by engine X as a completely new request meaning

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at this point here.

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The rewritten greet you are I start to right from the top again and will get re-evaluated again.

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The re-evaluation makes rewrites very powerful but also requires more system resources than say a return.

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Just something to keep in mind when creating rewrite rules.

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Okay once rewritten to slash greet this request will move past this rewrite so let's create a location

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to match add on.

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I'll change this one and return a simple 200 worth Hello user save reload the configuration.

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Keeping in mind what our rewrite checks for.

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I'll request slash user slash the first part of that rewrite rule John.

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The second part with the word match.

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Enter.

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Hello user.

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So clearly the response from slash greet although the browser is still pointing to slash user slash

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John meaning the request was rewritten internally only unbeknownst to the client.

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Another important and powerful feature of rewrites is the ability to capture certain parts of the original.

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You are right.

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Using standard regular expression capture groups or example let's say we want to capture a user name.

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This word character section of the regular expression simply wrap that part in braces like so.

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Which being the first capshaw group in this you are they can be accessed as dollar signs so a variable

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one should we have had a second caption Ruby here.

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Like this we could have access that value as dollar sign too and so on.

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OK so with this variant we're now requesting slash user slash John as we did in the browser and then

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rewriting that to slash greet slash John as that will be the value of this capture group.

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We can test this by creating an exact match location specifically for Slash greet slash John meaning

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any other user will be matched on the standard prefix match and only John.

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This exact match returned 200 Hello John.

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Reload these changes.

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And now what should happen when I refresh this is that slash user slash John should get rewritten to

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slash greet slash John revaluated as that new you are II so skipping past the rewrite and then even

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though this slash Greek location is a match I was slash greets slash John exact match will take priority

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and return.

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Hello John.

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Test it.

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And it works.

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Change this to any other user.

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However.

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Jane.

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And we get the prefix match with Hello user.

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Get the last part of rewrites.

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I'm going to cover is passing optional flags or one in particular the last flag to demonstrate.

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OK read another rewrite here.

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This time matching slash greet slash John and rewriting it to thumb dot B in G.

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The demo site image.

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Meaning that if we now request slash user slash John this first rewrite will matchett rewrite it to

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slash graetz lashed John and then have it re-evaluate it where it will then match the second rewrite

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and again be rewritten to thumb doppie in G and finally served as thumb dont be in G save and test this.

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Request John again.

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And sure enough we get the thumb image under this user slash John request.

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Now what the last flag allows us to do is essentially tell engine X not to allow you are right to be

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rewritten any more on this first rewrite add lost.

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So still re-evaluate the new you are right after the rewrite but make sure this is the last time it

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gets rewritten meaning it should skip over the second rewrite save reload request that same you are

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row with a reload and we're back to hello John.

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That wraps up redirects and rewrites.

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Although technically there's a third kind of rewrite called Try files which will cover in the next lesson.