G'day chickenlips,

Here's a solution using index and splice. (Obviously, you'll need to use your code to generate the random word - I've just allowed entering it from the command line for testing purposes.)

$ perl -Mstrict -Mwarnings -E '
print q{Random word: };
RAND: while (my $randword = <>) {
    chomp $randword;
    say "Input words using only letters in: $randword";
    INPUT: while (my $inword = <>) {
        chomp $inword;
        my @randchars = split q{} => $randword;
        my $char_count = 0;
        CHAR: for my $in_char (split q{}, $inword) {
            ++$char_count;
            my $pos = index join(q{} => @randchars), $in_char;
            if ($pos >= 0) {
                splice @randchars, $pos, 1;
            }
            else {
                say "Failed on char: $in_char (at position $char_count
+)";
                next INPUT;
            }
        }
        say "$inword OK";
    }
    print q{Random word: };
}
print "\n";
'
[download]

Here's a sample run:

Random word: qqwe
Input words using only letters in: qqwe
ew
ew OK
ewq
ewq OK
ewqq
ewqq OK
qewq
qewq OK
qqewq
Failed on char: q (at position 5)
qqqwe
Failed on char: q (at position 3)
Random word: aaaabcde
Input words using only letters in: aaaabcde
qwe
Failed on char: q (at position 1)
asd
Failed on char: s (at position 2)
abcdef
Failed on char: f (at position 6)
abcde
abcde OK
aaaab
aaaab OK
aaaaab
Failed on char: a (at position 5)
Random word: ^D
[download]