It's an alias:

marto@shemp ~ $ perlbrew use 5.16.0

A sub-shell is launched with 5.16.0 as the activated perl. Run 'exit' 
+to finish it.

bash-4.2$ exit
exit
marto@shemp ~ $ perlbrew use perl-5.16.0

A sub-shell is launched with perl-5.16.0 as the activated perl. Run 'e
+xit' to finish it.
[download]

Note that use is temporary, perlbrew switch version is permanent.