# Interpolation in Terraform

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1. Variable Interpolation:
    
    * `${var.variable_name}`: Interpolates the value of a variable.
        
2. Resource Attribute Interpolation:
    
    * `${resource_type.resource_name.attribute}`: Interpolates the value of a specific attribute of a resource.
        
3. Data Attribute Interpolation:
    
    * `${`[`data.data`](http://data.data)`_`[`type.data`](http://type.data)`_name.attribute}`: Interpolates the value of a specific attribute of a data source.
        
4. Output Interpolation:
    
    * `${output.output_name}`: Interpolates the value of an output variable.
        
5. String Interpolation:
    
    * `"${expression}"`: Interpolates a string with an expression.
        
6. List Interpolation:
    
    * `[element1, element2, ...]`: Interpolates a list of elements.
        
7. Map Interpolation:
    
    * `{key1 = value1, key2 = value2, ...}`: Interpolates a map of key-value pairs.
        
8. Conditional Interpolation:
    
    * `condition ? true_val : false_val`: Interpolates a value based on a condition.
        
9. Numeric Interpolation:
    
    * Arithmetic operations: `+`, `-`, `*`, `/`, `%`: Interpolates the result of arithmetic operations on numbers.
        
10. Splat Expression Interpolation:
    
    * `${resource_type.resource_name.*.attribute}`: Interpolates a list of values for a specific attribute of multiple resources.
        
11. Count Interpolation:
    
    * `${count.index}`: Interpolates the current index value when using resource or module count.
        
12. Element Interpolation:
    
    * `${list[index]}`: Interpolates a specific element from a list based on the index.
        
13. Lookup Interpolation:
    
    * `${lookup(map, key, default)}`: Interpolates the value of a key in a map and provides a default value if the key doesn't exist.
        
14. File Interpolation:
    
    * `${file(path)}`: Interpolates the content of a file at the specified path.
        
15. Templatefile Interpolation:
    
    * `${templatefile(path, vars)}`: Interpolates the content of a template file at the specified path, replacing variables with values from the `vars` map.
        
16. Join Interpolation:
    
    * `${join(delimiter, list)}`: Interpolates a string by joining elements of a list with the specified delimiter.
        
17. Lower and Upper Case Interpolation:
    
    * `${lower(string)}`: Interpolates a lowercase version of the given string.
        
    * `${upper(string)}`: Interpolates an uppercase version of the given string.
        
18. Regex Replace Interpolation:
    
    * `${replace(string, regex, replacement)}`: Interpolates a string by replacing substrings matching a regex pattern with a specified replacement.
        
19. JSON Interpolation:
    
    * `${jsonencode(data_structure)}`: Interpolates a JSON-encoded string representation of a data structure.
        
20. Terraform Function Interpolation:
    
    * `${function_name(arg1, arg2, ...)}`: Interpolates the result of a Terraform function call with the specified arguments.