# 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):

    # Requires that all env vars are set; otherwise returns None

    has_all = True

    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)

        if env_name in os.environ: vars_[name] = os.environ[env_name]

        else: has_all = False

    if has_all: return vars_

    else: return None

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_