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Variables

Introduction​

Postman supports a number of different variable "scopes":

  • Global
  • Collection
  • Environment
  • Data
  • Local

In this guide, we'll focus on Environment Variables. Environment variables are a way to store and reuse values across multiple requests in a collection, which can be particularly useful in our case for storing RPC endpoint URLs, addresses, and other values that are shared across multiple go-quai API requests.

Environment Variables​

The Example Quai Postman Environment includes a small number of pre-defined environment variables that you can use in your requests. These variables include:

  • chain
  • myAddress
  • txHash
  • blockNumber
info

This guide assumes you have already installed Postman and imported the Example Quai Postman Environment. If you have not done so, please refer to the Setting Up Postman guide.

The pre-configured environment variables can be accessed via the Environment tab in the top left of the Postman application:

PostmanEnvironmentVariables

To add your own environment variable, simply type your variable name in the Add new variable field at the bottom of the list and fill it in with the desired value.

Chain Specific Variables​

Quai Network has many distinct chains, each with their own sharded address space, state, and unique data. To send a request to a specific chain, you must define the chain environment variable with the chain name you want to interact with and ensure that all of the arguments you pass to the request are valid for that chain.

For example, to request balance data for my address on Cyprus 1, I need to:

  • set the chain environment variable to cyprus1 to route to the Cyprus 1 RPC endpoint
  • ensure that the myAddress parameter in the request is a valid Cyprus 1 address

If the data passed to the request is not valid on the specified chain, the request will return an error.

Usage​

Environment variables can be used in any request by wrapping the variable name in double curly braces ({{}}).

For example, all Quai Postman Collection requests use a {{chain}} variable to specify the chain to request data from in the RPC endpoint URL:

https://rpc.{{chain}}.colosseum.quaiscan.io
info

The {{chain}} variable is the only environment variable used by default in all requests. All other variables are optional and can be used as needed.

The same principle applies to any other defined environment variable. For example, if you define the {{txHash}} variable with your own transaction hash, you can use it in a request like this:

{
  "jsonrpc": "2.0",
  "method": "quai_getTransactionByHash",
  "params": [
    {{txHash}}
  ],
  "id": 1
}

When the request is sent, Postman will automatically replace {{chain}} with the value of the chain environment variable. You can hover over the {{}} to see the resolved value:

PostmanVariableHover