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We're getting the page title
from a URL parameter and

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we're using it to load in page
content from a text file.

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Now we just need to convert our
response to actual HTML and

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we can do that using ERB.

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Let's talk about the embedding
part of embedded Ruby.

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You store some static text,
usually HTML code, in a file.

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Then using specially ERB tags you
embed Ruby code into the static

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text that displays changing dynamic data.

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Each time the template is rendered each
piece of Ruby code is evaluated to

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get a result.

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Those results are inserted into
the template in place of the ERB tags,

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giving you text that changes each
time the template is rendered.

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Let's set up a temporary playground
where we can try out ERB text.

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I'm going to create a new get
route with a path of /test.

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It's important to place this
before the get title route in

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your code to avoid a conflict.

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We'll talk about the reason for
that later.

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Within the route block,
we'll call the ERB method and

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have it render a template called test.

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Then we'll create a new file in
the views directory called test.erb.

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The next time we visit the /test path,
it will render the contents of this file.

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There are two kinds of ERB, tags, regular
embedding tags and output embedding tags.

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Regular embedding tags start with <% and

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end with %>, they contain some Ruby
code in between those symbols.

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The code gets evaluated but the results
aren't placed directly into the output.

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So let's say I had a regular
tag like this, grade = 54.

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When the tag gets evaluated
the grade variable will be set but

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nothing will appear in the output.

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Regular embedding tags are most
frequently used for two things, loops and

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including or excluding parts of
the template based on the condition.

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If you include a conditional like an IF
expression in a regular embedding tag,

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any text inside the conditional will
only be included in the output if

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the condition is true.

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So let's say that I had
a statement up here,

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a regular ERB tag setting
the grade variable to 97.

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And then I'll put insert another ERB
tagged with a conditional in it.

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if grade, if the grade variable,
if the value in it is greater than 60,

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I'll put separate ERB tag down here with
the end keyword to end the if statement.

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Now anything contained inside that
conditional is only going to be printed

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if the conditional is true.

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So let's put a paragraph tag
in here saying you passed.

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If grade were lower than sixty, you passed
would not be included in the output.

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But since it's set to ninety seven,
it will be.

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Let's save this.

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And now let's restart our server.

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And try visiting the /test path.

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It loads the test.arb tag,

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evaluates the Ruby code setting
the grade variable to 97.

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Then it checks the conditional testing
whether the grade variable is greater

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than 60.

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And it is, so
it prints the paragraph tag, you passed.

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If we change the variable's
value to say 54,

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save that, and
reload the page, the condition

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will no longer be true and the you passed
HTML will be excluded from the output.

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By the way you may have noticed that
I didn't restart the app after making

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changes to the ERB template.

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That's because,

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unlike the main Ruby code, ERB templates
are reloaded each time they're rendered.

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So if you save changes
to the ERB template,

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they'll show up as soon as
you refresh your browser.

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The other common use of regular
embedding tags is in loops.

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If you place a loop in
a regular embedding tag,

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any text inside the loop lobby
will be output repeatedly.

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So let's say that I wanted to output three
paragraphs containing the word fish.

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We'll create a regular
embedding tag up here and

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we'll loop three times by calling the
times method on the integer object three.

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Times method takes a block which
loops that number of times.

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And since it's a do end block we need the
end keyword down here in a separate tag.

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Now any text we put inside the loop here
will be repeated that number of times.

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So let's put an HTML paragraph tag, and
we'll just put the word fish inside it.

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Save this and reload our page.

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And you see it loops three times,

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each time outputting an HTML
paragraph with the word fish.

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In addition to regular embedding tags,
ERB also has output

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embedding tags which begin with <%= and
end with %>.

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The equal sign at the start is the only
difference in how you type output tags

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versus regular tags.

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Like regular embedding tags the Ruby code
inside an output tag gets evaluated when

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the template is rendered.

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But unlike regular tags, the return
value of the Ruby code gets included in

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the template in place of the tag.

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So if we have an output embedding
tag with the math operation 2 + 2,

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when the template is rendered the code
will be evaluated and the result, four,

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will be included in the output.

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Similarly, we can place a call to
the time.now method in an output tag and

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we'll get the current time in the output.

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And because the values are updated
every time we render the template,

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we can refresh the page and
see a new result every time.

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We can mix regular embedding tags and
output embedding tags too.

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For example, we can nest an output
embedding tag inside an each block and

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the output tag will be
evaluated repeatedly.

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So let's say we wanted to print
an HTML paragraph element for

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each item in an array.

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We can set up the array within
a regular embedding tag.

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And the each method, if you recall,
loops through each element of the array,

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passing it to the argument
here in the block.

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Again this is a multi-line
block starting with do, so

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we're going to need the end keyword
in a separate tag down here.

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And any text here within
the loop will get repeated.

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So we're going to output an HTML paragraph
tag and we're going to embed within it

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the output number,
the current value of the number variable.

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Let's save this and reload our page.

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And we get the output 1 fish,
5 fish, 25 fish.

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It loops through each value and our array,
passes it into the number argument to

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the block, and then within the loop body
this output embedding tag gets evaluated.

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The current value of number is the result,
and that gets embedded into the output.

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So that's how to embed Ruby code
into an HTML template using ERB.

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We're done trying out ERB code for now, so

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let's go into the views directory and
delete the test.erb file.

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We'll also want to go into the main app
code and delete the get /text route