Yep, Data::Dumper for example will complain (under -w) about printing to an unopened file handle if you say

Actually its perl that complains here. The warning is provided because perl reads

print Dumper $quux;
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as

use IO::File;
Dumper->print($quux);
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when 'Dumper' is an unknown bareword. Personally I always disambiguate print statements in some way just because ive been bitten a few times.

Incidentally in this case its not much harder (and often desirable) to replace that with

print Data::Dumper->new([$quux],['quux'])->Dump(),"\n";
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I say desirable, and use the long winded ->new() form because now we can easily add stuff in the middle:

# we have large cyclic structures: disable pretty indent, enable purit
+y mode.
print Data::Dumper->new([$quux],['quux'])->Purity(1)->Indent(1)->Dump(
+),"\n";
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