$ time perl gen_random_strings.pl 2000000 60 70 ABC >s1

real    0m45.910s
user    0m44.647s
sys     0m1.091s
$ time perl gen_random_strings.pl 2000000 60 70 ABC >s2

real    0m45.989s
user    0m44.475s
sys     0m1.138s