Once upon a time I wrote a very simple sub to filter out non-printable characters on web-form input: 
sub filterCharacters
{
    my $text = shift;

    $text =~ s/[\000-\037]/ /g;
    $text =~ s/[\177-\777]/ /g;
    $text =~ s/\s+/ /g;

    return $text;
}

[download]
Then one day another developer came along and changed this sub to allow a character he thought was line-feed, but was actually Backspace (he was looking at the decimal value instead of octal): 
sub filterCharacters
{
    my $text = shift;

    $text =~ s/[\000-\009]/ /g;
    $text =~ s/[\011-\037]/ /g;
    $text =~ s/[\177-\777]/ /g;
    $text =~ s/\s+/ /g;

    return $text;
}

[download]
So here's the weird part, this manifested itself as each instance of the character '9' getting changed to a space.

We've fixed the problem, but I can't for the life of me figure out how allowing Backspace characters resulted in the 9's getting whacked?

Oh wise Monks, for the sake of my sanity and education, please enlighten me! Thanks.

In reply to Puzzler - filtering characters by rashley

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