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Welcome — this lesson explains intrinsic functions in AWS CloudFormation and shows common usage patterns and concise examples. Intrinsic functions let you compute or inject values into your template at deployment time, avoiding hard-coded properties and enabling reusable templates. In YAML templates, most intrinsic functions use a short form that begins with an exclamation mark (for example, !Ref). In JSON templates the same functions are available with the Fn:: or long form (for example, "Ref": "MyParam").
A slide titled "Intrinsic Functions" explaining that AWS CloudFormation built-in functions dynamically assign values to template properties. It shows icons for "Values" and "Template Properties" with example intrinsic functions listed (!Ref, !GetAtt, !Join, !Sub, !If, !Equals, !FindInMap).
Intrinsic functions are evaluated by CloudFormation when you create or update a stack. Use the YAML short form (e.g., !Ref) in YAML templates and the JSON long form (e.g., "Ref": "MyParam") in JSON templates.

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Quick reference table

FunctionPurposeYAML short form (example)
RefReturn a parameter value or a resource’s default return (often the physical ID)BucketName: !Ref InputBucketName
GetAttRetrieve a resource attribute such as an ARN or URLValue: !GetAtt MyBucket.Arn
JoinConcatenate a list of strings with a separator!Join ["-", [ !Ref DevName, !Ref BucketName ]]
SubSubstitute variables into a string using ${Var} syntaxObjectArn: !Sub "arn:aws:s3:::${InputBucketName}/*"
IfReturn one of two values depending on a ConditionSettings: !If [ IsProd, "ProdSettings", "DevSettings" ]
EqualsCompare two values (commonly used inside Conditions)!Equals [ X, "Production" ]
FindInMapRetrieve a value from the Mappings section!FindInMap [ DevMap, !Ref DevName, "Env" ]

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Ref

!Ref returns the value of a parameter or, for many resources, the resource’s physical ID or another default return value (for example, the name of an S3 bucket). Example — reference a parameter named InputBucketName: 
BucketName: !Ref InputBucketName
Use Ref to inject parameter values or to get the primary identifier of a created resource.

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GetAtt

!GetAtt retrieves a resource attribute, commonly an ARN, endpoint, or other generated attribute. In YAML you can use dot notation (e.g., MyBucket.Arn) or the list form ["MyBucket", "Arn"]. In JSON you must use the long form. Example — get the ARN of a bucket with logical ID MyBucket: 
Value: !GetAtt MyBucket.Arn
When using Fn::GetAtt in JSON, use the list form (["MyBucket", "Arn"]). The dot notation is YAML-specific convenience and may not translate directly to JSON.

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Join

!Join concatenates a list of values into a single string using a specified separator. Useful for building names, paths, or tag values. Example — combine a developer name and a bucket name with a dash: 
!Join ["-", [ !Ref InputDeveloperName, !Ref InputBucketName ]]
If InputDeveloperName is Arno-Pretorius and InputBucketName is bucket22, the result will be: Arno-Pretorius-bucket22

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Sub

!Sub substitutes variables into a string using ${VariableName} syntax. It’s ideal for constructing ARNs, resource strings, or any text that needs parameter/resource values embedded. Example — build an S3 object ARN using a parameter: 
ObjectArn: !Sub "arn:aws:s3:::${InputBucketName}/*"
This replaces ${InputBucketName} with the parameter value at deployment time. !Sub also supports a second parameter (a map) to override or provide custom substitutions.

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If

!If evaluates a named Condition (defined in the Conditions section) and returns one of two values depending on whether the condition is true or false. Example — return a settings string based on a condition named IsProd: 
Settings: !If [ IsProd, "ProdSettings", "DevSettings" ]
Conditions often use logical functions such as !Equals, !Not, !And, and !Or.

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Equals

!Equals compares two values and returns true if they are equal, false otherwise. It’s commonly used inside Conditions. Example — compare a mapped value to the string "Production": 
!Equals [ !FindInMap [ DevMap, !Ref InputDeveloperName, "Env" ], "Production" ]

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FindInMap

!FindInMap retrieves a value from the Mappings section using a three-part key: MapName, TopLevelKey, SecondLevelKey. Example — retrieve an environment assignment for a developer using a mapping named DevMap: 
!FindInMap [ DevMap, !Ref InputDeveloperName, "Env" ]
Nesting intrinsic functions is common (for example, using !FindInMap inside !Equals), and CloudFormation evaluates these at deployment time in the correct order.
Tip: Combine intrinsic functions to build dynamic names, ARNs, or conditional resource properties. For example, use !Sub with ${} placeholders that themselves are populated by !Ref or !GetAtt.
That covers the core intrinsic functions you’ll use most often. Parameters, Conditions, and Mappings are closely related—review those sections to see how intrinsic functions integrate across full CloudFormation templates.

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