The path to the input file will be passed into your program as a command line argument when your program is called. code example

Example 1: how to get command line arguments in python

#!/usr/bin/python

import sys

print 'Number of arguments:', len(sys.argv), 'arguments.'
print 'Argument List:', str(sys.argv)

Example 2: get input from command line and run command in c++

> args my_file.txt
Line fab
Line fab
Line edc