Also, leave the newline ending off the end of the die() statement. It supressses line number information. According to perlfunc, die:

If the last element of LIST does not end in a newline, the current script line number and input line number (if any) are also printed, and a newline is supplied.

Here is my favorite file opener. I have used it for a couple of years and used to routinely catch a lot of wierd errors due to my typing skills (or lack there of).

• It doesn't suppress line number info,
• It uses the three argument style for open,
• It uses one of those cool quote-like operators (qq{}),
• It uses the lower precedence or operator to avoid extra parentheses
• It uses a scalar ($fh) instead of a glob (FH) to hold the file handle and allows me to avoid local when passing file handles,
• It quotes the file name in the error message in case something wonky is going on with white space (or I screwed up the file name), and
• It looks good in my editor's syntax highlighter. :)

open my $fh, '<', $filename or die qq{Cannot open "$filename": $!};
open my $fh, '>', $filename or die qq{Cannot open "$filename": $!};
open my $fh, '>>', $filename or die qq{Cannot open "$filename": $!};
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I disagree completely with your first point. If you need to know on what line an I/O error occured, something is horribly wrong with your error handling. Users must not have to dig into a program to find and address the cause of errors under their control (as opposed to a programming error).

I agree with the other changes, but I didn't want to venture far from the topic until the OP's problem became known. How I write it:

open(my $fh_log, '>>', $qfn_log)
   or die(qq{Cannot open log file "$qfn_log": $!\n});
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