In order to define your own variables and reuse them in your tests, it’s easier to use the User Defined Variables from JMeter.
Here is how to create a variable and use it in an HTTP Request from your JMeter Test Plan.
Steps
1. Open JMeter (here is a more detailed post on how to install JMeter) and Add a Thread Group to your Test Plan
2. Add a HTTP Request Sampler to your Thread Group
3. Right-Click the Thread Group and add User Defined Variables Config Element in your JMeter test
4. Create a new variable: var1 with value www.example.com
5. Go to the HTTP Request and add the variable name where you want to be replaced with its value, use ${var1}
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