Hello world! with NO repetition

Perl 6 (29 28 characters)

This was somewhat annoying, but I finally managed to make a program for this task. Thanks go to the great #perl6 community, for helping me with this task. It took me two hours, hope you enjoy. The output is completely up to specification, including a newline.

say
Q[@A`DO world!]~|<HeLhg>

There are four tokens of interest.

• say

  This outputs the argument with new line at end. The new line after the command itself is needed as a space replacement.

• Q[@A`DO world!]

  This is the first string. Q[] is for raw strings (like r"" in Python). It can take any delimiter (or pair of them), in this case []. In this case, I use this for quotes, I don't need raw string behavior.

• ~|

  This is stringwise (~) bitwise or (|) operator.

• <HeLhg>

  <> is list literal, which takes space separated list of elements. In this case, it has one element, and used as a scalar, it gives a string.

Perl 5 with -M5.010, 29 bytes

say+He.v108
x2,q(O world!)^$"

Try it online!

I've gained a lot of knowledge since I first attempted this. Still not as short as the other answers, but the best I can come up with!

Perl 5.10+: 24 chars

say+He,YZX^q(567 world!)

OK, I think this is as short as it gets in Perl.

Run with perl -M5.010 (or just perl -E) to enable the Perl 5.10+ say feature.