The canonical solution is:

my $file = do {
   local $/;
   <>;
};
[download]

But, we're in Perl, so there's more than one way to do it.

  $file = join( '', <> );
[download]

also works. Of course, you could look at File::Slurp for a CPAN-based solution that's a little more readable.

PS. if you have an open filehandle in $fh, you would replace <> with <$fh> in the above, of course.