2**3
[download]

or

exp(log(2)*3)
[download]

** and other operators are documented in perlop. exp, log and other core functions (aka "named operators") are documented in perlfunc.

Update: Added the exp-log expression. It's not very useful in Perl, but I threw it in since it's useful in languages without an exponentiation operator or function. In fact, ** is probably implemented as the exp-log expression.