karls-mac-mini:~ karl$ perlbrew list perl-5.16.2 perl-5.16.3 perl-5.17.7 perl-5.18.0 perl-5.18.1 * perl-5.18.2 karls-mac-mini:~ karl$ perlbrew install --as perl-5.18.2threads -Dusethreads perl-5.18.2 Installing /Users/karl/perl5/perlbrew/build/perl-5.18.2 into ~/perl5/perlbrew/perls/perl-5.18.2threads This could take a while. You can run the following command on another shell to track the status: tail -f ~/perl5/perlbrew/build.perl-5.18.2.log karls-mac-mini:~ karl$ perlbrew list perl-5.16.2 perl-5.16.3 perl-5.17.7 perl-5.18.0 perl-5.18.1 * perl-5.18.2 perl-5.18.2threads karls-mac-mini:~ karl$ perlbrew switch perl-5.18.2threads karls-mac-mini:~ karl$ perlbrew list perl-5.16.2 perl-5.16.3 perl-5.17.7 perl-5.18.0 perl-5.18.1 perl-5.18.2 * perl-5.18.2threads karls-mac-mini:~ karl$ perl -Mthreads ^C