sys-系统特定的参数和功能

该模块提供对解释器使用或维护的一些变量的访问，以及与解释器强烈交互的函数。它始终可用。

代码如下

#!/usr/bin/python
# Filename: cat.py

import sys

def readfile(filename):
  '''Print a file to the standard output.'''
  f = file(filename)
  while True:
    line = f.readline()
    if len(line) == 0:
      break
    print line, # notice comma
  f.close()

# Script starts from here
if len(sys.argv) < 2:
  print 'No action specified.'
  sys.exit()

if sys.argv[1].startswith('--'):
  option = sys.argv[1][2:]
  # fetch sys.argv[1] but without the first two characters
  if option == 'version':
    print 'Version 1.2'
  elif option == 'help':
    print '''\
This program prints files to the standard output.
Any number of files can be specified.
Options include:
 --version : Prints the version number
 --help  : Display this help'''
  else:
    print 'Unknown option.'
  sys.exit()
else:
  for filename in sys.argv[1:]:
    readfile(filename)