$_=1x($l=pop);for$i(0..$l-1){($_=reverse)++for substr$_,$i;s/(.{$l}).+/$1/;print"\r$_";1e-5<rand&&redo}

##</code><code>##

-l15e'print|substr$_||=1x($l=pop),~rand$l,1,$A%10 while++$A%1e6||--$l'

##</code><code>##

-l15e'print|substr$_||=1x($l=pop),~rand$l,1,~~rand 10 while++$A%1e6||--$l'