You *could* do it that way. Here's what I came up with, just to be non-ASCII safe:

#!/usr/bin/perl -w

use strict;

my $offset = ord('A');
my $last = 26;
if (@_) {
    $last = 52;
}

print "Random Character Printer.  Press CTRL-D to stop.\n";

do {
    my $value = int rand(26) + $offset;
    print $value, "\t", chr($value);
} while (<>);
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Note that ASCII values between 91 and 97 inclusive may give you trouble, as A .. Z and a .. z aren't adjacent. You'll want to add a check for that. (Besides, I hadn't used a do-while loop in a while.)