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.

In reply to Mastermind, fixed by tinypig

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.