06 Variables

title: "Postman Variables: Global, Environment, Collection" description: "Use Postman variables across scopes: global, environment, collection, and local. Learn variable precedence, dynamic variables, data files, and variable management for flexible API testing." weight: 6 date: 2026-06-28 lastmod: 2026-06-28 tags: [api-development, postman] }

Postman variables store dynamic values that can be reused across requests. They come in four scopes: global (always available), environment (context-specific), collection (collection-specific), and local (request-scoped). Variables follow a precedence hierarchy.

What You'll Learn

• Variable scopes and precedence
• Environment variables for different deployments
• Collection variables for shared values
• Dynamic variables (timestamp, guid, random)
• Data variables from CSV/JSON files

Why It Matters

Variables eliminate hardcoded values, making collections reusable across environments. Environment variables enable switching between dev, staging, and production with one click.

Real-World Use

Postman collections for multi-environment deployments use environment variables for base URL, API keys, and database identifiers. Collection variables store resource IDs created during test runs.

flowchart TD
    Precedence[Variable Precedence] --> Data[Data Variables
Highest Priority]
    Data --> Local[Local Variables]
    Local --> Environment[Environment Variables]
    Environment --> Collection[Collection Variables]
    Collection --> Global[Global Variables
Lowest Priority]

Teacher Mindset

Use global variables for values that never change (API version). Use environment variables for deployment-specific values (URL, tokens). Use collection variables for values shared across requests (resource IDs). Use local variables for temporary values.

Code Examples

// Example 1: Setting and getting variables
// Set variables from response
const user = pm.response.json();
pm.collectionVariables.set('user_id', user.id);
pm.environment.set('auth_token', user.token);
pm.variables.set('temp_id', user.id); // Local variable

// Get variables
const baseUrl = pm.variables.get('base_url');
const token = pm.variables.get('auth_token');

// Check existence
const hasToken = pm.environment.has('auth_token');

// Example 2: Dynamic variables in pre-request
// Postman built-in dynamic variables
// {{$guid}} - Random UUID
// {{$timestamp}} - Current timestamp
// {{$randomInt}} - Random integer
// {{$randomEmail}} - Random email

pm.variables.set('order_id', '{{$guid}}');
pm.variables.set('created_at', '{{$timestamp}}');
pm.variables.set('customer_email', '{{$randomEmail}}');

// Custom dynamic value
const now = new Date();
pm.variables.set('today', now.toISOString().split('T')[0]);

// Example 3: Environment management
// Create environment variables programmatically
const environments = {
    dev: {
        base_url: 'http://localhost:3000',
        api_key: 'dev-key-123'
    },
    staging: {
        base_url: 'https://staging.api.example.com',
        api_key: 'staging-key-456'
    },
    production: {
        base_url: 'https://api.example.com',
        api_key: '{{prod_api_key}}' // Secret from CI
    }
};

// Switch environment in pre-request
const env = pm.environment.get('current_env') || 'dev';
const config = environments[env];
pm.environment.set('base_url', config.base_url);

Common Mistakes

• Hardcoding values instead of using variables
• Not understanding variable precedence (global vs environment conflicts)
• Storing secrets in collection variables visible to all team members
• Using wrong variable scope (environment vs collection)
• Not using dynamic variables for unique test data

Practice

1. Create a global variable for API version.
2. Create environment variables for base_url (dev, staging, prod).
3. Use collection variables to store a created resource ID.
4. Use {{$guid}} and {{$timestamp}} dynamic variables.
5. Challenge: Write a script that copies environment variables from one environment to another.

FAQ

Mini Project

Set up three environments (dev, staging, production) with base_url and api_key variables. Create a collection variable for tracking a user_id across requests. Use dynamic variables for creating unique test data. Write a pre-request script that selects the environment.

What's Next

Next, you will learn about pre-request scripts for setting up request data.