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- So one really useful
thing that Terrafrom

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has implemented are functions.

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Functions allow you to call

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out externally to retrieve values

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or calculate values outside your config.

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Now unfortunately, Terraform
does not have the ability

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for you to implement your
own functions directly

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so we'll talk about a little bit more

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in some later lessons

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if you do have that need

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but they have well over 100
built-in functions defined

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and they can do just all
kinds of different things.

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So let's just take a look

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at some of the more common ones

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that I find myself using

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and that you may use as well.

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Now, the syntax for calling a function

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is simply to embed the name

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of the function in your code

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and use the parentheses
for any parameters.

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You have to know the
names of these functions.

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They're all documented here.

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You can just follow this link

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and it will take you there.

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It'll tell you all the functions.

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It has 'em all broken out

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by function type like date/time functions,

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string functions, mathematical
functions, et cetera

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and then you can assign these to locals

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just like you can assign
any other expression.

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You can use them interpolations.

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You can use a function
within another function

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so I'll just show you some
of the syntax for that.

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It's pretty simple to understand.

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But it's a really powerful feature.

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So let's start off with
just some simple date

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and time functions.

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These are used quite frequently.

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This is the current timestamp.

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This is used all the time

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if you need to make a unique
name for an S3 buckets

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as our examples were.

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This is probably what
Terraform uses internally

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when they make their default names.

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This'll just give you a timestamp

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and then you can, formatdate
will give you the name

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or the month of the year.

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And this takes a standard
date format string

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and you can see we're
referencing something

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that we already assigned above

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so you can reference within
this same local block in here

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so this takes two arguments.

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It takes a format string

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and it takes a timestamp.

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And then if we wanted to
increment the day by one,

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we can call formatdate

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with telling it that we
just want to date to output

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and we can call the timeadd function

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so with timeadd, we're adding 24 hours

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to the timestamp so
that's gonna be tomorrow

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and this is gonna tell
us the day of the month.

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There's lots of numeric
functions in there.

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These aren't used quite
as often in my experience.

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Here we're using the minimum function.

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As I mentioned before in the last section,

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we had a bug here

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because we don't actually want

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to check whether or not this is zero.

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What we wanna do is check

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whether it's above the minimum.

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So the way to do that

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is to use this min function.

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This is gonna return
the lesser of the number

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of buckets or the bucket count.

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Actually I think we
actually want the max there

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so we have a bug on top of
a bug but you get the idea.

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It's a simple numeric function

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that compares two numbers

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and you can return the min
with the minimum function

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and the min or the mac.

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String functions are used very frequently.

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In fact, we used lower
earlier in this lesson.

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So lower, upper, trimspace
will remove any white space

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from the beginning or end of a string.

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Format, it's the same as the
C string formatting functions.

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So you give it a format string

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and you give it the
string to put it in there.

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This one's not so useful
because the interpolation

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in Terraform is actually
much more robust than this

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but it does have a list form

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so this will create hello

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and it'll take a list

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and it'll create four
strings all with that

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if that's useful.

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That can be useful.

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There're other interpolation
methods now in Terraform

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that may be more appropriate
than this for most cases

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and we'll talk about those later.

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So that's kinda how functions work.

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They're really simple
to get started in using

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by they can be really, really powerful.

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You can do things like generate UUIDs

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if you need a unique identifier.

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That's pretty powerful ability.

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You can look up values in a map,

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things like that are all
implemented in functions.