#Ruby: 27 characters

<!-- language: lang-ruby -->

    puts [:Hel,'o wor',"d!"]*?l

Sample run:

    bash-4.1# ruby <<ENDOFSCRIPT
    > puts [:Hel,'o wor',"d!"]*?l
    > ENDOFSCRIPT
    Hello world!

#Ruby: 25 characters

(Based on Vache's comment.)

<!-- language: lang-ruby -->

    puts 'He'+?l*2+"o world!"

#Ruby: 23 characters

(Copy of [Danko Durbić](https://codegolf.stackexchange.com/users/1308/danko-durbic)'s Powershell [answer](https://codegolf.stackexchange.com/a/18725/4198).)

<!-- language: lang-ruby -->

    puts"He#{?l*2}o world!"