On Sat, 20 Jan 1996, der Mouse wrote:

> Once more: this is a reasonable guess, but only a guess; it is
> perfectly valid for text files to start with %!, or PostScript programs
> to not start with a comment.  (Requiring PostScript code to start with
> a comment is as silly as cc refusing to compile something that doesn't
> start with /*.)

Nevertheless, Adobe has defined that a correctly conforming PostSript 
file starts with the two characters %!.

> As I mentioned and all these respondents who have been pointing at %!
> seem to have ignored, I have on occasion wanted to print _exactly the
> same file_ twice, once as as PostScript program to be run and once as a
> text file to be printed.  _No_ guessing mechanism that looks at only
> the contents of the file can possibly suffice.

Hey, nothing can ever be 100% perfect.  I'd say it's much better to have 
to do something explicit to get a PostScript file printed in source form 
than to have to explicitly request that it be treated as PostScript.

Automatic %! recognition does the job correctly in virtually every case,
and follows the principle of least astonishment.

-tih
-- 
Tom Ivar Helbekkmo
tih@Hamartun.Priv.NO