title: how to add flag in python
body: <p>currently i have a folder that contain many files and unique text
  basically there is
  1.txt
  2.txt
  3.txt</p>
  
  <p>the contain of 1.txt is 111111
  the contain of 2.txt is 222222
  the contain of 3.txt is 333333</p>
  
  <p>i have a script as below to print the contain of this txt file as below</p>
  
  <pre><code>from os import system
  import sys
  
  text=sys.argv[1]
  
  def loop():
      system("cat /root/Music/loop/"+text+".txt")
  
  
  if __name__ == "__main__":
      loop()
  </code></pre>
  
  <p>so now when i type python loop.py 1
  it will print out and display 
  111111</p>
  
  <p>when i type python loop.py 2
  it will print out and display 
  222222</p>
  
  <p>my question is how to i add a flag to print all?
  for example python loop.py --all</p>
  
  <p>111111</p>
  
  <p>222222</p>
  
  <p>333333</p>