title: How do I set a Jenkins environment variable based on a job parameter?
body: <p>I have a project where I need to set an environment variable based on a choice parameter the user chooses. Each project has a theme project dependency. I'd like to have the user choose the project and then load the theme name from a property file. Something like</p>
  
  <pre><code>proj1=theme1
  proj2=theme2
  proj3=theme3
  </code></pre>
  
  <p>If the user chooses <code>proj1</code> from the <code>PROJECT_NAME</code> choice parameter, I want to automatically set <code>THEME_NAME</code> to be <code>theme1</code>. What would be the best way to go about this?</p>
  
  <p>I don't want to modify the Jenkins job config whenever a new project is added. Instead, I want to have the mapping in a file so I can have it in version control.</p>