$ perlbrew exec --with 5.18.4,5.42.0 time -p perl -e '
>   $_ = 1 x 1e6;
>   1 while s/.$//;
> '
perl-5.18.4
==========
real 0.14
user 0.13
sys 0.00

perl-5.42.0
==========
real 18.95
user 18.94
sys 0.00