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* clarify input variables opening sentence * adjust variables description * claraify providers text and add learn callout * add description to providers page * add desscription and clarify provider configuration * add deprecation note to versions in proivder configs * add hands on callout and clarify next steps in intro * link to language collection from language docs * give more context about configurtion language up front * clarify output top page * reorganize for each intro to present feature before notes * move description before link out and remove passive voice * fix typo * clarify purpose of plan * move explanation before learn link and fully spell boolean * add a syntax heading to separate intro from details * add learn callout to module source docs * clean up intro to provider requirements and add link * Apply suggestions from code review Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com> * Apply suggestions from code review Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com> Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com>
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layout, page_title
| layout | page_title |
|---|---|
| language | Conditional Expressions - Configuration Language |
Conditional Expressions
A conditional expression uses the value of a boolean expression to select one of two values.
Hands-on: Try the Create Dynamic Expressions tutorial on HashiCorp Learn.
Syntax
The syntax of a conditional expression is as follows:
condition ? true_val : false_val
If condition is true then the result is true_val. If condition is
false then the result is false_val.
A common use of conditional expressions is to define defaults to replace invalid values:
var.a != "" ? var.a : "default-a"
If var.a is an empty string then the result is "default-a", but otherwise
it is the actual value of var.a.
Conditions
The condition can be any expression that resolves to a boolean value. This will usually be an expression that uses the equality, comparison, or logical operators.
Result Types
The two result values may be of any type, but they must both be of the same type so that Terraform can determine what type the whole conditional expression will return without knowing the condition value.
If the two result expressions don't produce the same type then Terraform will attempt to find a type that they can both convert to, and make those conversions automatically if so.
For example, the following expression is valid and will always return a string, because in Terraform all numbers can convert automatically to a string using decimal digits:
var.example ? 12 : "hello"
Relying on this automatic conversion behavior can be confusing for those who are not familiar with Terraform's conversion rules though, so we recommend being explicit using type conversion functions in any situation where there may be some uncertainty about the expected result type.
The following example is contrived because it would be easier to write the
constant "12" instead of the type conversion in this case, but shows how to
use tostring to explicitly convert a number to
a string.
var.example ? tostring(12) : "hello"