title: Code build setting environment variables in build steps
body: <p>I'm using codebuild to build an existing project and would like to add the version number to the artifact zip name. The build number is available in source code, but I need a way to expose this to the Artifacts codebuild step. </p>
  
  <p>Cut-down version of my buildspec.yaml:</p>
  
  <pre><code>env:
    exported-variables:
      - BUILD_VERSION
  phases:
    build:
      commands:
        - setx BUILD_VERSION (Get-Content -Path .\Version.txt) /M
  artifacts:
    base-directory: bin\Release\Publish\
    files:
      - .\**\*
    name: myapp-$BUILD_VERSION-$(Get-Date -UFormat "%Y%m%d%H%M%S").zip 
  </code></pre>
  
  <p>Currently this outputs "mpapp--.zip" Is there any way to set the BUILD_VERSION environment variable to the value from the file?</p>