random gen

[=||=cat]

so i've like many des and md5'nix to do, everything randomly generated 8 chars lowercase digits

kind like

xys3rkvq
iu23lmja
9ruyadf
.
.
.

first approach i tried the easy brain way, creating wl's of thousands of words to soon realize i was just loosing my time - sucess rate was not even 1% :\

then and now i was thinking in trying with custom charset masks
like

-1 ?l ?1?1?1?1 -2 ?d ?1 -3 ?l ?1?1?1

this would mean 8 chars lenght first 4 lowercase (a-z) 1 middle one digit(5ªposition 0-9) 3 last ones lowercase (a-z) , right?
if so how could i join all together to switch the digit position along the charset (from position 1 to 8) ?
if not...excuse my lammeness and show me the light, please.
thank you so much in advance.