Bash

HelloWorld.sh:

#!bin/sh

echo "Hello world!"

To run it:

$ chmod +x HelloWorld.sh
$ ./HelloWorld.sh

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

HelloWorld.php

<html>
<body>
<?php
echo "Hello world!";
?>
</body>
</html>

HelloWorld.py:

 print "Hello, World!"

To run it:

$ python HelloWorld.py

Alternatively:

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