in reply to <> oddity ?

while(<>)

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reads from STDIN. Try this script: 

while(<>) {
    print;
}

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This should behave similar to yours under your 3 scenarios. 

$ ./weird.pl sample.txt

whereas 

$ ./weird.pl <sample.txt

or

$ cat sample.txt | ./weird.pl

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 UPDATE: I am stupid and should read "Programming Perl" again. Apologies for posting useless stuff. No idea what goes wrong with your code.

In Section Seekers of Perl Wisdom