vars:
  http_proxies:
  - 192.168.1.5:3128
  - proxy5.internal.example.com:3128

tasks:

  - name: learn which proxy to use
    script: get_first_open_port.py {{ http_proxies | join( " " ) }}
    changed_when: false
    register: open_ports

  - set_fact:
      http_proxy: "{{ open_ports.stdout_lines[0] }}"
    when:
    - 'open_ports.stdout | length > 0'
    failed_when:
    - 'open_ports.stdout | length = 0'

  - name: use http_proxy environment variable
    script: script_needing_internet.sh -i {{ inputvar }}
    environment:
      http_proxy: "{{ http_proxy | default(omit) }}"