{
    # For the sake of the example, this assumes that you
    # want to limit the possible input to this range
    print "Please enter a number [1-9999]: ";
    chomp($in = <STDIN>);
    redo unless $in =~ /^\d+$/ && $in > 0 && $in <= 9999;
}

print join(",", 1 .. $in), "\n";