$ 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";
'