That sounds pretty nasty, but I'm having a hard time implementing it, so I'm not sure I'm getting your point. I tried this:

# nasty.pl

use strict;
use warnings;

$| = 1;

print 'first line: ', scalar <>;

while (<>) {
  print "first loop: $_";
}

while (<STDIN>) {
  print "second loop: $_";
}

__END__
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and called it with

% echo 'just another one-line file' > one-line_file
% yes junk | head -3 | perl nasty.pl one-line_file
first line: just another one-line file
second loop: junk
second loop: junk
second loop: junk
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I was expecting, from what you wrote, that the first loop would read STDIN, but that's not what the output shows (if I remove the second loop, the first loop still doesn't produce any output). What am I missing?