$^V isn't going to work for versions prior to 5.6.0, so $] may be the better option if you can't guarantee how old a version of Perl you'll be running.

$ perl5.00503 -le 'print $]'
5.00503
$ perl5.6.0 -le 'print $]'
5.006
$ perl5.6.1 -le 'print $]'
5.006001
[download]

Or, if you want to "pretty print" it...

$ perl5.00503 -le 'printf "v%d.%d.%d\n", $] =~ /^(\d+)\.(\d{3})(\d*)/'
v5.5.3
$ perl5.6.0 -le 'printf "v%d.%d.%d\n", $] =~ /^(\d+)\.(\d{3})(\d*)/'
v5.6.0
$ perl5.6.1 -le 'printf "v%d.%d.%d\n", $] =~ /^(\d+)\.(\d{3})(\d*)/'
v5.6.1
[download]

    --k.