If I have a one line program like this:
        print "Hello World!";
it doesn't work. No errors when I run it with the -w option, it just
does nothing. But if I also print a newline character it works fine:
        print "Hello World!\n";

Things that make you go hmmmm...if someone could explain what is
happening that would be great!

 perl hw.pl > out.txt

or to a pager

 perl hw.pl | more

  http://perl.plover.com/FAQs/Buffering.html

The obvious solution is to always output a newline character at the end.

You could also try:

$|=1;
print "Hello World!";
sleep 2;

Which should print Hello World! wait a couple of seconds and then exit (when
your prompt will erase the Hello World!).

The $| bit is to turn off buffering, this is explained in perlfaq5, under the
"How do I flush/unbuffer an output filehandle?  Why must I do this?" FAQ.

are you storing that in a file and then trying to run it?

i would do it like this, first store the following code in a text file called
hello.

#!/usr/bin/perl
print "Hello, World!";

then, make the script executable with the command:

chmod +x hello

Then run the program with the command:

./hello

You can also produce exactly the same output with the following program:

#!/usr/bin/perl

print <<HELLO;
Hello, World!
HELLO

I learnt this trick just today ;-)

Also, in the example you gave you did not say whether you included
#!/usr/bin/perl on the first line of your program.

I hope I have been able to help you.

Kind regards,

martin

  MS> print "Hello, World!";

  MS> You can also produce exactly the same output with the following program:

  MS> print <<HELLO;
  MS> Hello, World!
  MS> HELLO

that is not the same output. think carefully about why.

  MS> I learnt this trick just today ;-)

good. then i hope you learned that <<FOO (called a here doc) is NOT a
feature of print. too many newbies think that since it is used so often
with print.

and learn to not top post. read these pages:

        http://www.btinternet.com/~chiba/sbox/topposters.html
        http://www.uwasa.fi/~ts/http/quote.html
        http://www.geocities.com/nnqweb/nquote.html

uri