C++

HelloWorld.cc:

#include <iostream>
 
int main()
{
     std::cout << "Hello, world! This is C++.\n";
}

To run it:

$ g++ HelloWorld.cc -o hello.x
$ ./hello.x

Python

HelloWorld.py:

 print "Hello, World!"

To run it:

$ python HelloWorld.py

Alternatively:

$ python -c "print 'Hello World! \n'"