#Ruby: 27 characters
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.)
puts 'He'+?l*2+"o world!"
#Ruby: 23 characters
(Copy of Danko Durbić's Powershell answer.)
puts"He#{?l*2}o world!"