1) while (<$fh>) { ...

This will break if the first line of the file is 0, the second line will not be read.

Hmm. Funny, it doesn't seem to behave that way for me, and I wouldn't expect it to. The magical while(<>) statement (with or without an explicit file handle) is actually shorthand for while( defined( $_ = <> ))

Try it out with a file that has just "0\n" as the first line and anything after that on other lines -- I've tried it a number of ways, and the only way I could get it to stop at the first line was:

while ( <> > 0) ...
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which is admittedly the sort of thing that very few people would do inadvertently.