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# `Fn::Select`
<a name="intrinsic-function-reference-select"></a>

The intrinsic function `Fn::Select` returns a single object from a list of objects by index.

**Important**  
`Fn::Select` doesn't check for null values or if the index is out of bounds of the array. Both conditions will result in a stack error, so you should be certain that the index you choose is valid, and that the list contains non-null values.

## Declaration
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### JSON
<a name="intrinsic-function-reference-select-syntax.json"></a>

```
{ "Fn::Select" : [ index, listOfObjects ] }
```

### YAML
<a name="intrinsic-function-reference-select-syntax.yaml"></a>

Syntax for the full function name:

```
Fn::Select: [ index, listOfObjects ] 
```

Syntax for the short form:

```
!Select [ index, listOfObjects ]
```

## Parameters
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index  
The index of the object to retrieve. This must be a value from zero to N-1, where N represents the number of elements in the array.

listOfObjects  
The list of objects to select from. This list must not be null, nor can it have null entries.

## Return value
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The selected object.

## Examples
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### Basic example
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The following example returns: `"grapes"`.

#### JSON
<a name="intrinsic-function-reference-select-example0.json"></a>

```
{ "Fn::Select" : [ "1", [ "apples", "grapes", "oranges", "mangoes" ] ] }
```

#### YAML
<a name="intrinsic-function-reference-select-example0.yaml"></a>

```
!Select [ "1", [ "apples", "grapes", "oranges", "mangoes" ] ]
```

 

### Comma-delimited list parameter type
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You can use `Fn::Select` to select an object from a `CommaDelimitedList` parameter. You might use a `CommaDelimitedList` parameter to combine the values of related parameters, which reduces the total number of parameters in your template. For example, the following parameter specifies a comma-delimited list of three CIDR blocks:

#### JSON
<a name="intrinsic-function-reference-select-example1.json"></a>

```
"Parameters" : {
  "DbSubnetIpBlocks": {
    "Description": "Comma-delimited list of three CIDR blocks",
    "Type": "CommaDelimitedList",
      "Default": "10.0.48.0/24, 10.0.112.0/24, 10.0.176.0/24"
  }
}
```

#### YAML
<a name="intrinsic-function-reference-select-example1.yaml"></a>

```
Parameters: 
  DbSubnetIpBlocks: 
    Description: "Comma-delimited list of three CIDR blocks"
    Type: CommaDelimitedList
    Default: "10.0.48.0/24, 10.0.112.0/24, 10.0.176.0/24"
```

To specify one of the three CIDR blocks, use `Fn::Select` in the Resources section of the same template, as shown in the following sample snippet:

#### JSON
<a name="intrinsic-function-reference-select-example2.json"></a>

```
"Subnet0": {
  "Type": "AWS::EC2::Subnet",
    "Properties": {
      "VpcId": { "Ref": "VPC" },
      "CidrBlock": { "Fn::Select" : [ "0", {"Ref": "DbSubnetIpBlocks"} ] }
    }
}
```

#### YAML
<a name="intrinsic-function-reference-select-example2.yaml"></a>

```
Subnet0: 
  Type: AWS::EC2::Subnet
  Properties: 
    VpcId: !Ref VPC
    CidrBlock: !Select [ 0, !Ref DbSubnetIpBlocks ]
```

 

### Nested functions with short form YAML
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The following examples show valid patterns for using nested intrinsic functions with the `!Select` short form. You can't nest short form functions consecutively, so a pattern like `!GetAZs !Ref` isn't valid.

#### YAML
<a name="intrinsic-function-reference-select-example3.yaml"></a>

```
AvailabilityZone: !Select 
  - 0
  - !GetAZs 
    Ref: 'AWS::Region'
```

#### YAML
<a name="intrinsic-function-reference-select-example4.yaml"></a>

```
AvailabilityZone: !Select 
  - 0
  - Fn::GetAZs: !Ref 'AWS::Region'
```

## Supported functions
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For the `Fn::Select` index value, you can use the `Ref` and `Fn::FindInMap` functions.

For the `Fn::Select` list of objects, you can use the following functions:
+ `Fn::FindInMap`
+ `Fn::GetAtt`
+ `Fn::GetAZs`
+ `Fn::If`
+ `Fn::Split`
+ `Ref`