The sys module (https://docs.python.org/3/library/sys.html) allows interacting with the Python run-time interpreter. One of the functions of the sys module is parsing command-line arguments provided as inputs to the program. Let's write a program that reads and prints the contents of the file that is passed as an argument to the program:

import sys
if __name__ == "__main__":
    with open(sys.argv[1], 'r') as read_file:
        print(read_file.read())

Try running the preceding example as follows:

python3 sys_example.py read_lines.txt

The preceding example is available for download along with this chapter as sys_example.py. The list of command-line arguments passed while running the program are available as a argv list in the sys module. argv[0] is usually the name of the Python program and argv[1] is usually the first argument passed to the function.

When sys_example.py is executed with read_lines.txt as an argument, the program should print the contents of the text file:

I am learning Python Programming using the Raspberry Pi Zero.
This is the second line.
Line 3.
Line 4.
Line 5.
Line 6.
Line 7.