How to use host environment variables

Development
1

For Drone-runner-exec,How to use host environment variables? such as maven,java…I write .sh file:
----------.drone.yml
kind: pipeline
type: exec
name: deployment

platform:
os: linux
arch: amd64

steps:

  • name: greeting
    commands:
    • echo hello world
    • bash ./build.sh
      when:
      branch:
      • main
        -------build.sh
        #!/bin/bash
        mvn --version
        java -version

mvn java these commads report errors：not found