Yeah, this bugs me too.
I *think* this is really a shell vs. Finder issue, and I don't know what
the fix is, but generally it seems like if you want to work on a
collection of files, the Finder can operate on that collection as a set --
hence opening PDFs together in Preview, or a directory or a directory tree
full of MP3s in iTunes, etc -- but if you do the same sort of thing from
the command line, it's as if you sent out a series of commands such as
"open -a foo bar1; open -a foo bar2; open -a foo bar3;" etc.
Annoying.
To date, I haven't found a way around this. The issue is broader than just
Preview & PDFs though -- something the Finder is doing allows collections
of files to be handled as a single set, and nothing I've tried from the
command line has been able to reproduce that functionality.
It isn't a command line vs. Finder issue. It has to do with how the information is passed to the app - in one lump, or one at file at a time.
Not having the source code for open, I don't know how it is implemented.
One could have implemented it to send a single 'odoc' apple event with a list of files, or by using one of the LaunchServices APIs that takes a list of files or urls, and it would have done what you wanted.
Jim
