Please kindly explain this error message

rovf has asked for the wisdom of the Perl Monks concerning the following question:

Recently I got the following error message, issued in one of the library modules I'm using:

Can't use an undefined value as a symbol reference
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Could someone please explain to me what it means? If the error would be reproducible, I would put use diagnostics in this module, but so far the error has occured only once. The code in question looks like this:

print $fh $params{message} or die "Cannot write to '$self->{filename}': $!";

I wonder whether, by some chance, $fh got undef here, but then I would have expected to see something like can not write to undefined file handle. What is a 'symbol reference'? Is it that (deprectaed?) feature where you could use a string, denoting another variable, to indirectly refer to that variable?

--
Ronald Fischer <ynnor@mm.st>

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Re: Please kindly explain this error message by Anonymous Monk on Sep 28, 2009 at 07:51 UTC
`echo Can't use an undefined value as a symbol reference at foo line 1. +\|splain Can't use an undefined value as a symbol reference at foo line 1 (#1) (F) A value used as either a hard reference or a symbolic referenc +e must be a defined value. This helps to delurk some insidious errors.` [download]	[reply] [d/l]
Re^2: Please kindly explain this error message by rovf (Priest) on Sep 28, 2009 at 08:19 UTC
Thanks for telling about `splain`. Great tool! -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l] [select]
Re: Please kindly explain this error message by Anonymous Monk on Sep 28, 2009 at 07:53 UTC
I think $fh is undef `$ perl -Mdiagnostics -Mstrict -we ' my $fh = shift; print $fh 1' Can't use an undefined value as a symbol reference at -e line 1 (#1) (F) A value used as either a hard reference or a symbolic referenc +e must be a defined value. This helps to delurk some insidious errors. Uncaught exception from user code: Can't use an undefined value as a symbol reference at -e line +1. at -e line 1` [download]	[reply] [d/l]