# Program options processing

import os

def env_flag(name): return name in os.environ and os.environ[name] != ''

def get_env_vars(names, prefix=None, env_names_ref=None):

    vars_ = {}

    for name in names:

        env_name = name

        if prefix != None: env_name = prefix+'_'+env_name

        if env_names_ref != None: env_names_ref.append(env_name)

        try: vars_[name] = os.environ[env_name]

        except KeyError: pass

    return vars_

def env_usage(env_names, optional=False):

    str_ = 'env'

    for name in env_names:

        str_ += ' '

        if optional: str_ += '['

        str_ += name+'=...'

        if optional: str_ += ']'

    return str_