I'd like to expand upon this correct answer. It seems like a really weird distinction if you aren't familiar with Perl's filter-writing magic. 
while (<DATA>) { ... }

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One might think that the above code is equivalent to this: 
@foo = <DATA>;
while (@foo) { ... }

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In reality, due to Perl's magical way of helping you implement simple STDIN-to-STDOUT text file filters, the first snippet is rephrased internally to mean the following: 
while (defined ($_ = readline(*DATA))) { ... }

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Thus, while () isn't taking a list, or even what looks like a list. It's taking a condition, the condition being the successful ability to read a single line from a filehandle (and if successful, assigning the line to $_ for checks inside the loop).

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[ e d @ h a l l e y . c c ]

In reply to Re^2: why can't I just cat the file??? by halley
in thread why can't I just cat the file??? by convenientstore

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