#!/usr/bin/perl -w

sub q { 
    $; = 1;                        # $; stores how many tries you've h
+ad; start at 1
    for (0..3) { 
        $;[$_] = int(rand(9))      # @; stores the correct four number
+s; set it up here
    }
} 

sub _ {
    print @_
}

&q;

for (;;) {
    $: = $~ = 0;        # set $: (right number in the right spot) and 
+$~ (right number) to 0
    _ "$/$; ";          # prints a newline then the number of tries yo
+u've had
    $_ = <>;            # read a line into $_
    
    if (/^\d{4}$/) {    # if the line is exactly 4 digits...
        @q = split //;  # @q holds the 4 digits
        
        --$#q;          # set $#q = 3, ignoring the newline at $q[4]
        $@ = -1;        # set $@ to -1
        
        # This loops through the input digits and checks for correctne
+ss
        
        for (@q) {                         # set $_ to each of the 4 i
+nput digits
            $a = $_;                       # set $a to the current dig
+it (why not leave it $_?)
            ($a == $;[++$@]) && ++$:       # increment $: if you have 
+a right number in the right spot
                || (grep /$a/, @;) && ++$~ # else increment $~ if you 
+have a right number in the wrong spot
        }
        
        _ "$~W$:B ";  # print out the total of right/wrong ($~W) and r
+ight/right ($:B)
        ++$;;         # increment number of tries
        
        $: == 4       # if we have four right numbers all in the right
+ spots
            | $; > 10 # or we have already had 10 tries
            && _ (@;) # print out the correct answer
            && &q     # and start the game over
    }
}
[download]

Taking a quick cursory look, I'd assume due to grep /$a/, @;

Makeshifts last the longest.

Nice work. I was reviewing it and I honestly don't remember why I did that (it's been a while since I originally wrote it). The only thing I can think is that I might have been concerned about overwriting the digit. I did have a quit (q) command in there when it was longer, though that is just a shot in the dark. With your suggestion implemented, it does seem to work fine:

sub q{$;=1;for(0..3){$;[$_]=int(rand(9))}}sub _{print@_}&q;for(;;){$:=
+$~=0
;_"$/$; ";$_=<>;if(/^\d{4}$/){@q=split//;--$#q;$@=-1;for(@q){($_==$;[+
++$@]
)&&++$:||(grep/$_/,@;)&&++$~}_"$~W$:B ";++$;;$:==4|$;>10&&_(@;)&&&q}}
[download]

Actually, it doesn't. As per Aristotle's suggestion above, the (grep/$_/,@;) would return true every time, thus always telling you you had four correct numbers.

Given hidden pattern: 8565

7566 -->> 1W2B (should be 0W2B, right?)
6566 -->> 2W2B (should also be 0W2B)

Eek, you're right. I just checked the Mastermind rules and it should not work like that. That is how I coded it to work, however. Here's a quick hack that seems to correct the problem... now to fix the obfuscated version...

#!/usr/bin/perl -w

sub q { 
    $; = 1;                        # $; stores how many tries you've h
+ad; start at 1
    for (0..3) { 
        $;[$_] = int(rand(9))      # @; stores the correct four number
+s; set it up here
    }
} 

sub _ {
    print @_
}

&q;

for (;;) {
    $: = $~ = 0;        # set $: (right number in the right spot) and 
+$~ (right number) to 0
    _ "$/$; ";          # prints a newline then the number of tries yo
+u've had
    $_ = <>;            # read a line into $_
    
    if (/^\d{4}$/) {    # if the line is exactly 4 digits...
        @q = split //;  # @q holds the 4 digits
        
        --$#q;          # set $#q = 3, ignoring the newline at $q[4]
        $@ = -1;        # set $@ to -1
        
        # This loops through the input digits and checks for correctne
+ss
        
        my @j = @;;
        for (@q) {                   # set $_ to each of the 4 input d
+igits
            ($_ eq $j[++$@]) && ++$: && ($j[$@]='X') && ($q[$@]='Y')
        }
        for (@q) {                   # set $_ to each of the 4 input d
+igits
            $a = $_;                 # set $a to the current digit (wh
+y not leave it $_?)
            (grep /$a/, @j) && ++$~  # else increment $~ if you have a
+ right number in the wrong spot
        }
        
        _ "$~W$:B ";  # print out the total of right/wrong ($~W) and r
+ight/right ($:B)
        ++$;;         # increment number of tries
        
        $: == 4       # if we have four right numbers all in the right
+ spots
            | $; > 10 # or we have already had 10 tries
            && _ (@;) # print out the correct answer
            && &q     # and start the game over
    }
}
[download]