> ## Documentation Index
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> Use this file to discover all available pages before exploring further.

# injectModifier

> **injectModifier**(`funcName`, `variables`, `userFilePath`, `diffPath`, `modifierFile`): `void`

Injects a modifier into a Solidity contract file by modifying its content.

This function performs the following operations:

1. Adds an import statement for `RulesEngineClientCustom` after the pragma line.
2. Updates the contract declaration to inherit from `RulesEngineClientCustom`.
3. Adds a `checkRulesBefore` modifier to the specified function with the provided arguments.
4. Writes the modified content back to the file and generates a diff file showing the changes.

## Parameters

| Parameter      | Type     | Description                                                                                                                                      |
| -------------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| `funcName`     | `string` | The name of the function to which the modifier will be added.                                                                                    |
| `variables`    | `string` | A comma-separated string of variables to be passed to the modifier. Supported types include `address`, `uint256`, `string`, `bool`, and `bytes`. |
| `userFilePath` | `string` | The file path of the Solidity contract to be modified.                                                                                           |
| `diffPath`     | `string` | The file path where the diff of the changes will be saved.                                                                                       |
| `modifierFile` | `string` | -                                                                                                                                                |

## Returns

`void`

## Remarks

* The function assumes the Solidity file uses standard formatting for pragma, contract declaration, and function definitions.
* The `checkRulesBefore` modifier is added to the calling function with the provided arguments.
* The diff file is generated in a format that highlights added and removed lines.

## Throws

Will throw an error if the file at `userFilePath` cannot be read or written.

## Throws

Will throw an error if the provided function name or variables are invalid.

## Defined in

[src/codeGeneration/inject-modifier.ts:63](https://github.com/forte-service-company-ltd/forte-rules-engine-sdk/blob/5aad4d7c3c8cc91280e4449c17ac8ea31219fbed/src/codeGeneration/inject-modifier.ts#L63)