Your output file is already in the directory when you glob so your output file is treated as an input. Move the glob before the open. 
    my @allFiles = glob("$severityDir/*.txt");
    open( my $fh, '>>', $severityFile )
        or die "Could not open file '$severityFile' $!";

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Bill

In reply to Re: Getting duplicate file contents in perl by BillKSmith
in thread Getting duplicate file contents in perl by noviceuser

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