JAVASCRIPT

postman environment variables

pm.environment.set("variable_key", "variable_value");

postman environment variables in body

{ "customer_id" : "{{cust_id}}" }

postman environment variable

postman.setGlobalVariable("refresh_token",postman.getResponseHeader("Refresh_token") );

postman test set environment variable

postman.setEnvironmentVariable("VARIABLE_NAME", <<VALUE>>);

postman setup environment

pm.environment.get("variable_key");

Postman Variables

just like variables in Java. 
we can create variables in postman to reuse the value 
1.Global variables: accessible everywhere in same workspace 
2.Environment variables: accessible in selected environment 
3.Collection Variables: belong to the collection itself and 
only accessible within the collection