The binmode and diamond ops are part of perl's buffered IO scheme. Sysread is a lower level system read, similar to the C library's read function. To use sysread as if <> were acting, you need to check if @ARGV has anything in it. If not, sysread from STDIN, otherwise open each filename in @ARGV and sysread until done.

Close, but not completely accurate.

binmode is not part of the buffered IO scheme - in fact, the last bit of the perldoc for binmode explicitly says:

binmode() is not only important for readline() and print() operations, but also when using read(), seek(), sysread(), syswrite() and tell() (see the perlport manpage for more details). See the "$/" and "$\" variables in the perlvar manpage for how to manually set your input and output line-termination sequences.

Now, as far as the original post is concerned, if you are only ever worried about a single argument in ARGV, this would be sufficient:

if (! @ARGV) {
  use open ':raw'; # implicit binmode on each open
  open(ARGV, '-');
} else {
  use open ':raw';
  open(ARGV, shift @ARGV); # Yeah, it's the two-arg version,
                           # because that's what perl does with <>
                           # see perlopentut
}
# ... now go do all that sysread stuff.
[download]

If, however, there are possibly multiple files available, you'll have to get more creative:

my @files = (@ARGV)?@ARGV:qw(-);
NEXTFILE:
while (@files) {
  use open ':raw';
  open(ARGV, shift @files);
  # do sysread stuff here
  # don't forget that an eof here may not be a "real" eof,
  # but a signal to go to the next file
}
[download]

Another possibility is to tie several files together into a single hash which does all the opening in the background. That's left as an exercise for the reader, of for some other response.

Update: Oops, as Mr. Muskrat pointed out. Fixed.

--


@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
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In your first snippet, you've reversed what needs to happen.

if (@ARGV) { # something's in @ARGV so we'll use it
  use open ':raw'; # implicit binmode on each open
  open(ARGV, shift @ARGV); # Yeah, it's the two-arg version,
                           # because that's what perl does with <>
                           # see perlopentut
} else {     # nothing's in @ARGV so we'll use STDIN
  use open ':raw'; # implicit binmode on each open
  open(ARGV, '-');
}
# ... now go do all that sysread stuff.
[download]

The open.pm pragma is what should allow you to set binmode for the "magic" @ARGV-based <>, but it doesn't. A patch to make this happen would be pretty simple if <> were fixed to not be an exploit source.

However, p5p insists that the input operator, <>, must be able to react to "perl -ne *" by opening output handles to create files (if there are any files whose names start with ">") or run arbitrary commands (if there are any files whose names start with "|").

This stopped my working on the patch to fix open.pm to be useful for <>.