In order to read a file form command line using Python, the script you want to use for it needs to accept a CLI argument. For example, say you want to write a cat command in python(a command that dumps all file content on the terminal). In order to do that, you could simply write a program:
import sys with open(sys.argv, 'r') as f: contents = f.read() print contents
If you save this file as cat.py and run it using:
$ python cat.py my_file.txt
This will take the my_file.txt and pass it to cat.py as a CLI argument in variable argv(second command line argument) which we can use to get the file and its contents.