Demo code, please. Your description is inaccurate (file handles don't have file names), and I can't reproduce the problem by guessing what you meant. 
$ perl -Te'
    my $fn = $ARGV[0];
    ($fn) = $fn =~ /^([a-zA-Z0-9]{1,8}\.txt)\z/ or die;
    open(my $fh, ">", $fn) or die;
    printf $fh "%s\n", "foo";
' foo.txt

$ cat foo.txt
foo

[download]

Update: Oops, missed the bit about writing tainted info, but it makes no difference 

$ perl -Te'
    my $fn = $ARGV[0];
    ($fn) = $fn =~ /^([a-zA-Z0-9]{1,8}\.txt)\z/
        or die;
    open(my $fh, ">", $fn) or die;
    printf $fh "%s\n", $ARGV[0];
' foo.txt

$ cat foo.txt
foo.txt

$ perl -Te'
    my $fn = $ARGV[0];
    ($fn) = $fn =~ /^([a-zA-Z0-9]{1,8}\.txt)\z/
        or die;
    open(my $fh, ">", $fn) or die;
    print $fh $ARGV[0];
    print $fh "\n";
' foo.txt

$ cat foo.txt
foo.txt

[download]

In reply to Re: Taint, CGI and perl 5.10 by ikegami
in thread Taint, CGI and perl 5.10 by nextguru

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