I debated adding this to my original obfuscated Mastermind perl, but it is a different script now which I worked hard to re-write, and despite changing the functionality pretty significantly, I was able to do it in only three characters more. 
sub q{$;=1;$q='';$q.=int(rand(9))for(5..8)}sub _{print@_}&q;for(;;){$:
+=$~=0;_
"$/$; ";chop($_=<>);if(/^\d{4}$/){$_.=q,_._,.$q;$:++while+s/(.)(.{6})\
+1/;$2,/
;$~++while+s/(.)(...+)\1/;$2$1/;_"$~W$:R ";++$;;$:==4|$;>10&&_($q)&&&q
+}}

[download]
(Though it was my idea to use substitution to evaluate the guess, thanks to diotalevi for showing me how to implement my idea: Re: Replace zero-width grouping?), This game follows the official Mastermind Instructions with the only difference being that I use 0-9, instead of 6 colors, to comprise the "code".

Added - How to play:

Consult the Mastermind Instructions if you are unfamiliar with how the original game is played. This demonstration shows how my script is used to play the game: 
perl mind.pl

1 1234
Program prompts with '1', which indicates the first guess. Player guesses '1234'. 
1W0R
Program responds with 1 white peg and no red pegs. 
2 5678
1W0R 
3 9900
0W0R 
4 1122
0W2R 
5 1155
0W0R 
6 6622
0W2R 
7 7722
0W2R 
8 8822
0W4R 8822
4 red pegs followed by the answer shows the player guessed the code correctly before his ten tries were exceeded.

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